Changes

[InstCombine] Pre-commit of test case showing miscompile bug in
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

[InstCombine] Fix miscompile bug in canEvaluateShuffled
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