<br><br><div class="gmail_quote">On Tue, Aug 6, 2013 at 1:42 PM, Adve, Vikram Sadanand <span dir="ltr"><<a href="mailto:vadve@illinois.edu" target="_blank">vadve@illinois.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<blockquote type="cite">Message: 6<br>
Date: Tue, 6 Aug 2013 10:46:19 -0400<br>
From: Chad Rosier <<a href="mailto:chad.rosier@gmail.com" target="_blank">chad.rosier@gmail.com</a>><br>
To: llvmdev <<a href="mailto:llvmdev@cs.uiuc.edu" target="_blank">llvmdev@cs.uiuc.edu</a>><div class="im"><br>
Subject: [LLVMdev] Potential SimplifyCFG optimization;<span style="white-space:pre-wrap">
</span>hammock to<br>
<span style="white-space:pre-wrap"></span>diamond transformation<br></div>
Message-ID:<br>
<span style="white-space:pre-wrap"></span><<a href="mailto:CAMo3wbR6x1wBzb17=GrkERV7kvzx2RdpuheFzyxkQEs3BBvKaw@mail.gmail.com" target="_blank">CAMo3wbR6x1wBzb17=GrkERV7kvzx2RdpuheFzyxkQEs3BBvKaw@mail.gmail.com</a>><br>
Content-Type: text/plain; charset="iso-8859-1"<div class="im"><br>
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All,<br>
I have some code that looks like the following:<br>
<br>
{<br>
double a, b, c;<br>
for (...) {<br>
...<br>
a = lots of FP math;<br>
b = lots of FP math;<br>
c = lots of FP math;<br>
if (cond) {<br>
a = 0.0;<br>
b = 0.1;<br>
c = 0.2;<br>
}<br>
...<br>
}<br>
}<br>
<br>
Could we not convert the hammock into a diamond and move the initial<br>
computation of a, b, and c into the else block. Something like this:<br>
</div></blockquote>
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</div>
I believe what you're proposing would be accomplished by PRE, since the stores to a, b and c are partially redundant, and once those are "placed" by PRE, the FP math would then get placed as you want as well.
<br></div></blockquote><div><br><br>Yes, that makes perfect sense.<br> </div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="word-wrap:break-word">
<div><div><div class="im"><blockquote type="cite"><br>
{<br>
double a, b, c;<br>
for (...) {<br>
...<br>
if (cond) {<br>
a = 0.0;<br>
b = 0.1;<br>
c = 0.2;<br>
} else {<br>
a = lots of FP math;<br>
b = lots of FP math;<br>
c = lots of FP math;<br>
}<br>
...<br>
}<br>
}<br>
<br>
Does a similar optimization exist? </blockquote>
<div><br>
</div>
</div><div>SSAPRE existed in LLVM but has been removed. PRE is one of those optimizations that are simply more efficient and also sometimes more effective as a bitvector dataflow optimization than as an SSA algorithm.</div>
<div class="im">
</div></div></div></div></blockquote><div><br>Good to know.<br> </div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="word-wrap:break-word">
<div><div><div class="im">
<br>
<blockquote type="cite"> If not, would the SimplifyCFG pass be<br>
an appropriate home for such an optimization?<br>
</blockquote>
<div><br>
</div>
</div><div>If done there, it is likely to only handle special cases like the above. My guess is that it is better done as a code motion pass than a SimplifyCFG extension.</div></div></div></div></blockquote><div><br>Thanks for the feedback, Prof. Vikram. You have been very helpful.<br>
<br></div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="word-wrap:break-word"><div><div><blockquote type="cite">
Chad<br>
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<div><span style="font-family:monospace">--Vikram Adve</span><br style="font-family:monospace">
<span style="font-family:monospace">Professor, Department of Computer Science</span><br style="font-family:monospace">
<span style="font-family:monospace">University of Illinois at Urbana-Champaign</span><br style="font-family:monospace">
<span style="font-family:monospace"><a href="mailto:vadve@illinois.edu" target="_blank">vadve@illinois.edu</a></span></div>
<div><span style="font-family:monospace"><a href="http://llvm.org" target="_blank">http://llvm.org</a></span></div>
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