<div dir="ltr">Hmm, what if we have:<div><br></div><div>volatile store i32 0, i32* %p</div><div>call void @llvm.assume(i1 false)</div><div>...</div><div><br></div><div>Can't this sort of logic let us sink the store past the assume? What if the assume gets replaced with unreachable?</div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jun 14, 2016 at 1:33 PM, Sanjoy Das via llvm-commits <span dir="ltr"><<a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Forgot to mention in the commit message: this regression was<br>
introduced in <a href="http://reviews.llvm.org/rL272489" rel="noreferrer" target="_blank">http://reviews.llvm.org/rL272489</a><br>
<div class="HOEnZb"><div class="h5"><br>
On Tue, Jun 14, 2016 at 1:23 PM, Sanjoy Das via llvm-commits<br>
<<a href="mailto:llvm-commits@lists.llvm.org">llvm-commits@lists.llvm.org</a>> wrote:<br>
> Author: sanjoy<br>
> Date: Tue Jun 14 15:23:16 2016<br>
> New Revision: 272703<br>
><br>
> URL: <a href="http://llvm.org/viewvc/llvm-project?rev=272703&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=272703&view=rev</a><br>
> Log:<br>
> [ValueTracking] Calls to @llvm.assume always return<br>
><br>
> This change teaches llvm::isGuaranteedToTransferExecutionToSuccessor<br>
> that calls to @llvm.assume always terminate. Most other relevant<br>
> intrinsics should be covered by the "CS.onlyReadsMemory() ||<br>
> CS.onlyAccessesArgMemory()" bit but we were missing @llvm.assumes<br>
> because we state that it clobbers memory.<br>
><br>
> Added an LICM test case, but this change is not specific to LICM.<br>
><br>
> Modified:<br>
> llvm/trunk/lib/Analysis/ValueTracking.cpp<br>
> llvm/trunk/test/Transforms/LICM/assume.ll<br>
><br>
> Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=272703&r1=272702&r2=272703&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=272703&r1=272702&r2=272703&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)<br>
> +++ llvm/trunk/lib/Analysis/ValueTracking.cpp Tue Jun 14 15:23:16 2016<br>
> @@ -3478,7 +3478,8 @@ bool llvm::isGuaranteedToTransferExecuti<br>
> // but it's consistent with other passes. See <a href="http://llvm.org/PR965" rel="noreferrer" target="_blank">http://llvm.org/PR965</a> .<br>
> // FIXME: This isn't aggressive enough; a call which only writes to a<br>
> // global is guaranteed to return.<br>
> - return CS.onlyReadsMemory() || CS.onlyAccessesArgMemory();<br>
> + return CS.onlyReadsMemory() || CS.onlyAccessesArgMemory() ||<br>
> + match(I, m_Intrinsic<Intrinsic::assume>());<br>
> }<br>
><br>
> // Other instructions return normally.<br>
><br>
> Modified: llvm/trunk/test/Transforms/LICM/assume.ll<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/assume.ll?rev=272703&r1=272702&r2=272703&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/assume.ll?rev=272703&r1=272702&r2=272703&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/test/Transforms/LICM/assume.ll (original)<br>
> +++ llvm/trunk/test/Transforms/LICM/assume.ll Tue Jun 14 15:23:16 2016<br>
> @@ -1,6 +1,7 @@<br>
> ; RUN: opt -licm -basicaa < %s -S | FileCheck %s<br>
><br>
> -define void @f(i1 %p) nounwind ssp {<br>
> +define void @f_0(i1 %p) nounwind ssp {<br>
> +; CHECK-LABEL: @f_0(<br>
> entry:<br>
> br label %for.body<br>
><br>
> @@ -31,4 +32,20 @@ for.end104:<br>
> ret void<br>
> }<br>
><br>
> +define void @f_1(i1 %cond, i32* %ptr) {<br>
> +; CHECK-LABEL: @f_1(<br>
> +; CHECK: %val = load i32, i32* %ptr<br>
> +; CHECK-NEXT: br label %loop<br>
> +<br>
> +entry:<br>
> + br label %loop<br>
> +<br>
> +loop:<br>
> + %x = phi i32 [ 0, %entry ], [ %x.inc, %loop ]<br>
> + call void @llvm.assume(i1 %cond)<br>
> + %val = load i32, i32* %ptr<br>
> + %x.inc = add i32 %x, %val<br>
> + br label %loop<br>
> +}<br>
> +<br>
> declare void @llvm.assume(i1)<br>
><br>
><br>
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<br>
<br>
<br>
</div></div><span class="HOEnZb"><font color="#888888">--<br>
Sanjoy Das<br>
<a href="http://playingwithpointers.com" rel="noreferrer" target="_blank">http://playingwithpointers.com</a><br>
</font></span><div class="HOEnZb"><div class="h5">_______________________________________________<br>
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