<html><head><meta http-equiv="Content-Type" content="text/html charset=iso-8859-1"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div><br><div><div>On Jun 27, 2014, at 4:23 PM, Philip Reames <<a href="mailto:listmail@philipreames.com">listmail@philipreames.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">
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Just to make sure I understand the issue properly, the key change
here is adding the *operands* rather than *users* to *a* worklist
right? We could potentially add them to the outer worklist and get
the same benefit?<br>
<br>
Looking through the code, we only seem to add the users of a
particular instruction to the worklist. For the sinking code, it
does make sense to reprocess the operands since sinking the original
instruction may have opened up further opportunities. <br>
<br>
As a side note, I do find myself somewhat wondering why we mix
transforms and placement here. The addition of the sinking code
stands out in this loop. Anyone know why this is done here rather
than another pass? Just curious about the history. <br>
<br>
Philip<br>
<br>
<div class="moz-cite-prefix">On 06/27/2014 01:17 PM, Aditya
Nandakumar wrote:<br>
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Thanks Chandler for your review.
<div>The problem I saw in a few test cases was that instcombine
had finished visiting all instructions (Iteration#0) and the
only possible changes were sinking of instructions. This sinking
of one instruction opened up sinking opportunities for other
instructions which were only being used by the current(sunk)
instruction. Since we are visiting top-down, there is only one
instruction being sunk per iteration.</div>
<div>So in some my test cases, instcombine ran for 8 iterations
where in iterations 1-8, it sank one instruction per iteration.
The test cases are about 150-300 lines long and we are visiting
all those instructions every iteration even though the only
change possible is the sinking.</div>
<div><br>
</div>
<div>Consider the following example. </div>
<div>bb1: %d0 = ...</div>
<div><span class="Apple-tab-span" style="white-space:pre"> </span>%d1
= .. %d0..</div>
<div>
<div><span class="Apple-tab-span" style="white-space:pre"> </span>%d2
= .. %d1..</div>
<div><span class="Apple-tab-span" style="white-space:pre"> </span>%d3
= op %d2 ..</div>
<div> <span class="Apple-tab-span" style="white-space:pre"> </span>...</div>
<div>bb2:</div>
<div> .. = op %d3</div>
</div>
<div><br>
</div>
<div>Currently instcombine would sink d3 in Iteration#0, d2 in
Iteration#1, d1 in Iteration#2 and d0 in Iteration#3 - but it
only requires one iteration in all.</div>
<div><br>
</div>
<div>Updated patch - removed C style comments and fixed typo(I
think).</div>
<br>
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<div>On Jun 26, 2014, at 5:54 PM, Chandler Carruth <<a moz-do-not-send="true" href="mailto:chandlerc@google.com">chandlerc@google.com</a>>
wrote:</div>
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<div dir="ltr">I don't immediately understand why this is
such a performance improvement here (and not elsewhere
in instcombine)... Do you have any insight into that? Is
it a locality problem that we don't re-visit the other
sinkable instructions in the right order? It feels
pretty weird to have a worklist-inside-a-worklist, so
I'm just trynig to understand it better...
<div>
<br>
</div>
<div>Also, the patch has a bunch of typos in comments
and uses C-style comments...</div>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Mon, Jun 23, 2014 at 10:57
PM, Aditya Nandakumar <span dir="ltr"><<a moz-do-not-send="true" href="mailto:aditya_nandakumar@apple.com" target="_blank">aditya_nandakumar@apple.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi
All<br>
<br>
I want to make a small optimization for instcombine.
While sinking instructions (with single use) to the
use block, also check if any other instructions
which are used in the current instruction (operands)
can be sunk.<br>
<br>
This speeds up InstCombine time in several cases as
previously only one instruction would be sunk per
iteration.<br>
<br>
Please review<br>
<br>
Thanks<br>
<span class="HOEnZb"><font color="#888888">Aditya<br>
</font></span><br>
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