<div dir="ltr">Thanks for digging into this!<div><br></div><div>Some comments inline:<br><div class="gmail_extra"><br><br><div class="gmail_quote">On Sat, Dec 28, 2013 at 4:39 PM, Chandler Carruth <span dir="ltr"><<a href="mailto:chandlerc@google.com" target="_blank">chandlerc@google.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">Well, after some more prodding, I dug into this *much* more deeply. I can now explain rather precisely the change to bzip2 which causes this patch to improve performance, and interestingly I no longer think this patch is the correct approach. Read on, because this was fun. However, be forewarned, this is more of a blog post than an email. =]<div>
<br></div><div><div>
<br></div><div>So first, let's all get on the same page about exactly what performance problem I'm seeing this patch address (Jim, I *think* when we talked this was the one you were looking at as well, but lemme know if not, I wasn't 100% certain). Here is a snippet of code produced by Clang with this patch reverted for the really hot inner function in the main loop of bzip2 (I've based all my benchmarks and measurements on v1.0.6, the latest open source release):</div>
<div><br></div><div><a href="http://paste2.org/0YGNdVJV" target="_blank">http://paste2.org/0YGNdVJV</a><br></div><div><ol style="margin:0px 0px 0px 45px;padding:0px 0px 0px 1px;border-width:0px 0px 0px 1px;border-left-style:solid;border-left-color:rgb(204,204,204);font-family:InconsolataMedium,monospace;font-size:13px;line-height:16px;vertical-align:baseline;list-style-position:initial;color:rgb(40,40,40);background-color:rgb(248,248,248)">
<li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># BB#2: # %if.end</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rsi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rax</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rbp</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%bl</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmpb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%bl</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">jne</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">.LBB27_1</span></div>
</li></ol></div><div><br></div><div>Now, originally the theory was that cmpb was being slow because if you make it a cmpl it sped up (for me, by around 3.5%). This is what this patch does:</div><div><br></div><div><a href="http://paste2.org/Y7D8cIcV" target="_blank">http://paste2.org/Y7D8cIcV</a><br>
</div><div><ol style="margin:0px 0px 0px 45px;padding:0px 0px 0px 1px;border-width:0px 0px 0px 1px;border-left-style:solid;border-left-color:rgb(204,204,204);font-family:InconsolataMedium,monospace;font-size:13px;line-height:16px;vertical-align:baseline;list-style-position:initial;color:rgb(40,40,40);background-color:rgb(248,248,248)">
<li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># BB#3: # %if.end</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rsi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rax</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rbp</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebx</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmpl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">jne</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">.LBB27_1</span></div>
</li></ol><div><font color="#880000" face="InconsolataMedium, monospace"><span style="line-height:16px;white-space:pre-wrap"><br></span></font></div></div>Ok, cool, this goes faster, but *why*? I was thinking it was around a partial register stall, but I didn't really understand where the stall came from. So I tried switching the above code back to 'cmpb':<div>
<br></div><div><a href="http://paste2.org/h0MbL2jM" target="_blank">http://paste2.org/h0MbL2jM</a><br></div><div><ol style="margin:0px 0px 0px 45px;padding:0px 0px 0px 1px;border-width:0px 0px 0px 1px;border-left-style:solid;border-left-color:rgb(204,204,204);font-family:InconsolataMedium,monospace;font-size:13px;line-height:16px;vertical-align:baseline;list-style-position:initial;color:rgb(40,40,40);background-color:rgb(248,248,248)">
<li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># BB#3: # %if.end</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rsi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rax</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rbp</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebx</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmpb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%bl</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">jne</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">.LBB27_1</span></div>
</li></ol></div><div><br></div><div>What I didn't expect was that this was just as fast (at least for me on the sandybridge machine I was testing on primarily). This got me thinking about how partial register stalls come to be. You write to one portion of the register, and then it gets merged with whatever was already in the high bytes. Well, there are kind of two places where that could happen in the original example (movb, movb, cmpb): either when we write the partial register with movb, or when we read it with cmpb. For more discussion of this from Intel, see their Optimization Reference Manual section 3.5.2.4.</div>
<div><br></div><div>But because we read it with the 'b' suffix, we don't actually read the high bytes! So we shouldn't be seeing a stall on the read side. So it seems like (at least on sandybrige) there is merging of partial registers on *write* even without a read.</div>
</div></div></blockquote><div><br></div><div>Interesting. This seems contrary to Agner's Sandy Bridge information in section 9.11 of <<a href="http://www.agner.org/optimize/microarchitecture.pdf">http://www.agner.org/optimize/microarchitecture.pdf</a>> "There is no penalty for writing to a partial register unless there is a later read from a larger part of the same register". Maybe you could share your findings with him?<br>
</div><div><br></div><div>-- Sean Silva</div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div dir="ltr"><div><div> Then the movb would be enough to cause the slowdown regardless of how we read it. This at least explains the measured performance shifts I see on my sandybridge. When I take the original assembly for all of bzip2, and I modify just these movb instructions to be movzbl, I see roughly the same performance uplift as we get with ToT and Jim's patch.<br>
</div><div><br></div><div>Ok, so it seems that on sandybridge (and I think haswell but I don't have one handy to test as thoroughly) it is important that when we don't need the high bytes of a register for an operation and we are going to movb or movw into it, we use movzbl or movzwl (resp.) to remove the false dependency at write time on the high bytes. I think that would accomplish what this patch set out to do, but in a much more targeted way. It will also catch many more of these issues because movb has the potential to cause this, not just those feeding 'cmp'.</div>
<div><br></div><div>Also, the measurements I dave done indicate that once we do the above, this patch should be reverted. I can't find any performance problems with either 8-bit cmpb (or 16-bit cmpw other than the 1-byte prefix cost in encoding), and using the more precisely sized cmp instructions lets us fold one of the two memory operands above into the cmp instruction. One thing I'm still confused by is why the original code didn't do that fold.</div>
<div><br></div><div>Here is what I would intuitively expect:</div>
<div><br></div><div><a href="http://paste2.org/KgLfPD8g" target="_blank">http://paste2.org/KgLfPD8g</a></div><div><ol style="margin:0px 0px 0px 45px;padding:0px 0px 0px 1px;border-width:0px 0px 0px 1px;border-left-style:solid;border-left-color:rgb(204,204,204);font-family:InconsolataMedium,monospace;font-size:13px;line-height:16px;vertical-align:baseline;list-style-position:initial;color:rgb(40,40,40);background-color:rgb(248,248,248)">
<li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># BB#2: # %if.end</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebx</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rsi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline">(</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline">,</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%rbp</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline">),</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(0,0,255)">cmpb</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%al</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline">,</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline">(</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline">,</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%rbx</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline">)</span><br>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(0,0,255)">jne</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(136,0,0)">.LBB27_1</span></li>
</ol><br>Note that I started from the original version (without this patch) and manually applied this (and all of the other stuff I'm about to discuss). I'm also re-register allocating here. It'll become more obvious later why. =] There is no effective change. we're now loading only one side of the comparison into a register, zext-ing it to ensure no false dependency, and directly pulling the other byte from memory.</div>
<div><br></div><div>However, there is a lot more wrong. Let's start off with the simple and obvious stuff. Why are we taking up two more registers and doing lea's just to add a displacement to the addresses? The addressing modes using the results have an empty displacement! So now we have this:</div>
<div><br></div><div><div><a href="http://paste2.org/mXZmU0df" target="_blank">http://paste2.org/mXZmU0df</a></div><div><ol style="margin:0px 0px 0px 45px;padding:0px 0px 0px 1px;border-width:0px 0px 0px 1px;border-left-style:solid;border-left-color:rgb(204,204,204);font-family:InconsolataMedium,monospace;font-size:13px;line-height:16px;vertical-align:baseline;list-style-position:initial;color:rgb(40,40,40);background-color:rgb(248,248,248)">
<li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># BB#2: # %if.end</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rsi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmpb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdi)</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">jne</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">.LBB27_1</span></div>
</li></ol></div><div><br></div><div>Cool, this looks really nice now, and benchmarking confirms it. But before we can actually do either of these transforms, we'll also have to fix how this is being used. Time for a more complete example:</div>
<div><br></div><div><a href="http://paste2.org/MjW043aZ" target="_blank">http://paste2.org/MjW043aZ</a><br></div><div><ol style="margin:0px 0px 0px 45px;padding:0px 0px 0px 1px;border-width:0px 0px 0px 1px;border-left-style:solid;border-left-color:rgb(204,204,204);font-family:InconsolataMedium,monospace;font-size:13px;line-height:16px;vertical-align:baseline;list-style-position:initial;color:rgb(40,40,40);background-color:rgb(248,248,248)">
<li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># BB#2: # %if.end</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">leal</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rsi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rax</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rbp</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%bl</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmpb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%bl</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">jne</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">.LBB27_1</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">
</div></li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># ... snip ...</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">
</div></li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(160,160,0)">.LBB27_1:</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># %if.then</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmpb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%bl</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">setb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(160,160,0)">.LBB27_37:</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># %return</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">popq</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rbx</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">popq</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rbp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">ret</span></div>
</li></ol></div><div><br></div><div>Ok, WTF. We 'cmpb %bl, %al', jump, and then 'cmpb %al, %bl'???? This makes no sense. *every* predecessor looks like this. The reason for the LB27_37 label sneaking around there is because there are even more blocks which end in essentially the same thing but with different registers instead of %al and %bl. Whatever the registers, its always the same pattern: "cmp X, Y; jne ....; cmp Y, X; setb %al". And if we didn't re-do the "cmp", it wouldn't have mattered that they were different registers!!! So lets fix that:</div>
<div><br></div><div><a href="http://paste2.org/z2gwXvAY" target="_blank">http://paste2.org/z2gwXvAY</a><br></div><div><ol style="margin:0px 0px 0px 45px;padding:0px 0px 0px 1px;border-width:0px 0px 0px 1px;border-left-style:solid;border-left-color:rgb(204,204,204);font-family:InconsolataMedium,monospace;font-size:13px;line-height:16px;vertical-align:baseline;list-style-position:initial;color:rgb(40,40,40);background-color:rgb(248,248,248)">
<li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># BB#2: # %if.end</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rsi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">),</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmpb</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">1</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdx</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%rdi</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">)</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">jne</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">.LBB27_1</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="color:rgb(64,128,128);font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit"># ... <snip> ...</span><br>
</div></li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<br></li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(160,160,0)">.LBB27_1:</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># %if.then</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">seta</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%al</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">ret</span></div>
</li></ol></div><div><br></div><div>Yea, that's a bit more plausible. =] Note that the 'popq' are gone because while when we fold away all of the lea's we no longer need the two scratch registers. The .LBB27_37 is cone because we no longer have 6 copies re-doing a comparison with different registers.</div>
<div><br></div><div>One final tweak that is totally unrelated to the rest of this. We're missing a DAG combine for the latch of the inner loop here which looks like this:</div><div><br></div><div><a href="http://paste2.org/aO0hBw1O" target="_blank">http://paste2.org/aO0hBw1O</a><br>
</div><div><ol style="margin:0px 0px 0px 45px;padding:0px 0px 0px 1px;border-width:0px 0px 0px 1px;border-left-style:solid;border-left-color:rgb(204,204,204);font-family:InconsolataMedium,monospace;font-size:13px;line-height:16px;vertical-align:baseline;list-style-position:initial;color:rgb(40,40,40);background-color:rgb(248,248,248)">
<li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># BB#36: # %if.end396</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># in Loop: Header=BB27_14 Depth=1</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">addl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">$8</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%edi</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">addl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">$8</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%esi</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">xorl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmpl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%r8d</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%edi</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%r8d</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmovbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">subl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%edi</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmpl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%r8d</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%esi</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">movl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%r8d</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">cmovbl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%eax</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">subl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%ebp</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%esi</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">decl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">(</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%r9</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">)</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">addl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">$</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">-</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(102,102,102)">8</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%r10d</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">jns</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">.LBB27_14</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">jmp</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">.LBB27_37</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">
</div></li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># ... <snip> ...</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(160,160,0)"><br>
</span></div></li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(160,160,0)">.LBB27_37:</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;font-style:italic;vertical-align:baseline;color:rgb(64,128,128)"># %return</span><br>
</div></li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(0,0,255)">movzbl</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%al</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline">,</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%eax</span><br>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(0,0,255)">popq</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%rbx</span><br>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(0,0,255)">popq</span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(25,23,124)">%rbp</span><br>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit"> </span><span style="font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;margin:0px;padding:0px;border:0px;vertical-align:baseline;color:rgb(0,0,255)">ret</span></li>
</ol></div><div><br></div><div>I'm always really suspicious when I see cmp followed closely by sub. Indeed, this is a case of us not realizing that the cmp and sub can be combined. When we do that, we also remove this last use of a scratch register (%ebp), confirming that we can get rid of all the popq business. When we do, we also no longer need to jmp, we can just directly ret:</div>
<div><br></div><div><a href="http://paste2.org/v5K9COgf" target="_blank">http://paste2.org/v5K9COgf</a><br></div><div><ol style="margin:0px 0px 0px 45px;padding:0px 0px 0px 1px;border-width:0px 0px 0px 1px;border-left-style:solid;border-left-color:rgb(204,204,204);font-family:InconsolataMedium,monospace;font-size:13px;line-height:16px;vertical-align:baseline;list-style-position:initial;color:rgb(40,40,40);background-color:rgb(248,248,248)">
<li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># BB#36: # %if.end396</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:italic;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(64,128,128)"># in Loop: Header=BB27_14 Depth=1</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">addl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">$8</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%edi</span></div>
</li><li style="margin:0px 0px 0px 3px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;white-space:pre-wrap">
<div style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline"> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(0,0,255)">addl</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(136,0,0)">$8</span><span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline">,</span> <span style="margin:0px;padding:0px;border:0px;font-family:inherit;font-size:inherit;font-style:inherit;font-variant:inherit;font-weight:inherit;line-height:inherit;vertical-align:baseline;color:rgb(25,23,124)">%esi</span></div>
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</li></ol></div><div><br></div><div>Yea, that looks more like sane code. =]</div><div><br></div><div>All of this combines for another 3.5% on bzip2 on sandybridge, despite just changing the mainGtU function manually by hand.</div>
<div><br></div><div>I'll probably break out some of these issues into bugs and such once I have more minimal test cases. I think the most important thing is to get the correct fix for partial register stalls on sandybridge committed and revert this patch so we don't keep paying a tax for a halfway fix. The rest is gravy, if very interesting all the same.</div>
<div><br></div><div>Just for reference, here is the complete asm before and after:</div><div><br></div><div>Before: <a href="http://paste2.org/CC50nde3" target="_blank">http://paste2.org/CC50nde3</a></div><div>After: <a href="http://paste2.org/J3DHbPJC" target="_blank">http://paste2.org/J3DHbPJC</a></div>
<div>- 100 fewer instructions</div><div>- 30% smaller encoded size after assembling</div><div>- 7% faster on sandybridge, 3.5% faster than with this patch (r195496)</div>
</div><div><br></div><div><br></div><div>Also for context, the benchmarking was done with a little compression algorithm benchmarking tool that I'm working to open source and will hopefully add to the test suite soon after. It's based on bzip2 1.0.6 (latest sources) and I primarily measured performance by compressing linux-3.12.tar with it.</div>
<span class=""><font color="#888888">
<div><br></div><div>-Chandler</div></font></span></div></div>
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<br></blockquote></div><br></div></div></div>