<div dir="ltr">The bug is at least four years old so it isn't a regression.  However, the fix is quite low risk.  I think it cannot hurt to merge it in to 3.8</div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Feb 1, 2016 at 11:06 AM, Hans Wennborg <span dir="ltr"><<a href="mailto:hans@chromium.org" target="_blank">hans@chromium.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">3.8?<br>
<div class="HOEnZb"><div class="h5"><br>
On Mon, Feb 1, 2016 at 9:37 AM, David Majnemer via llvm-commits<br>
<<a href="mailto:llvm-commits@lists.llvm.org">llvm-commits@lists.llvm.org</a>> wrote:<br>
> Author: majnemer<br>
> Date: Mon Feb  1 11:37:56 2016<br>
> New Revision: 259375<br>
><br>
> URL: <a href="http://llvm.org/viewvc/llvm-project?rev=259375&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=259375&view=rev</a><br>
> Log:<br>
> [InstCombine] Don't transform (X+INT_MAX)>=(Y+INT_MAX) -> (X<=Y)<br>
><br>
> This miscompile came about because we tried to use a transform which was<br>
> only appropriate for xor operators when addition was present.<br>
><br>
> This fixes PR26407.<br>
><br>
> Modified:<br>
>     llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp<br>
>     llvm/trunk/test/Transforms/InstCombine/icmp.ll<br>
><br>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=259375&r1=259374&r2=259375&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=259375&r1=259374&r2=259375&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)<br>
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Mon Feb  1 11:37:56 2016<br>
> @@ -3877,7 +3877,7 @@ Instruction *InstCombiner::visitICmpInst<br>
>                                  BO1->getOperand(0));<br>
>            }<br>
><br>
> -          if (CI->isMaxValue(true)) {<br>
> +          if (BO0->getOpcode() == Instruction::Xor && CI->isMaxValue(true)) {<br>
>              ICmpInst::Predicate Pred = I.isSigned()<br>
>                                             ? I.getUnsignedPredicate()<br>
>                                             : I.getSignedPredicate();<br>
><br>
> Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=259375&r1=259374&r2=259375&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=259375&r1=259374&r2=259375&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)<br>
> +++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Mon Feb  1 11:37:56 2016<br>
> @@ -1672,3 +1672,15 @@ define i1 @cmp_slt_rhs_inc(float %x, i32<br>
>    %cmp = icmp slt i32 %conv, %inc<br>
>    ret i1 %cmp<br>
>  }<br>
> +<br>
> +; CHECK-LABEL: @PR26407<br>
> +; CHECK-NEXT: %[[addx:.*]] = add i32 %x, 2147483647<br>
> +; CHECK-NEXT: %[[addy:.*]] = add i32 %y, 2147483647<br>
> +; CHECK-NEXT: %[[cmp:.*]] = icmp uge i32 %[[addx]], %[[addy]]<br>
> +; CHECK-NEXT: ret i1 %[[cmp]]<br>
> +define i1 @PR26407(i32 %x, i32 %y) {<br>
> +  %addx = add i32 %x, 2147483647<br>
> +  %addy = add i32 %y, 2147483647<br>
> +  %cmp = icmp uge i32 %addx, %addy<br>
> +  ret i1 %cmp<br>
> +}<br>
><br>
><br>
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</div></div></blockquote></div><br></div>