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Summary:
Add restrictions in canEvaluateShuffled to prevent that we for example
transform
%0 = insertelement <2 x i16> undef, i16 %a, i32 0
%1 = srem <2 x i16> %0, <i16 2, i16 1>
%2 = shufflevector <2 x i16> %1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
into
%1 = insertelement <2 x i16> undef, i16 %a, i32 1
%2 = srem <2 x i16> %1, <i16 undef, i16 2>
as having an undef denominator makes the srem undefined (for all
vector elements).
Fixes: https://bugs.llvm.org/show_bug.cgi?id=43689
Reviewers: spatel, lebedev.ri
Reviewed By: spatel, lebedev.ri
Subscribers: lebedev.ri, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69038
llvm-svn: 375208
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canEvaluateShuffled
Adding the reproducer from https://bugs.llvm.org/show_bug.cgi?id=43689,
showing that instcombine is doing a bad transform. It transforms
%0 = insertelement <2 x i16> undef, i16 %a, i32 0
%1 = srem <2 x i16> %0, <i16 2, i16 1>
%2 = shufflevector <2 x i16> %1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
into
%1 = insertelement <2 x i16> undef, i16 %a, i32 1
%2 = srem <2 x i16> %1, <i16 undef, i16 2>
The undef denominator makes the whole srem undefined.
llvm-svn: 375207
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