[InstCombine] Do not exercise nested max/min pattern on abs

Summary:
This is a fix for assertion failure in
`getInverseMinMaxSelectPattern` when ABS is passed in as a select pattern.

We should not be invoking the simplification rule for
ABS(MIN(~ x,y))) or ABS(MAX(~x,y)) combinations.

Added a test case which would cause an assertion failure without the patch.

Reviewers: sanjoy, majnemer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D30051

llvm-svn: 295719

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index b5718c3a9e0..dcfacc2e7d9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -785,7 +785,9 @@ Instruction *InstCombiner::foldSPFofSPF(Instruction *Inner,
   // This transform is performance neutral if we can elide at least one xor from
   // the set of three operands, since we'll be tacking on an xor at the very
   // end.
-  if (IsFreeOrProfitableToInvert(A, NotA, ElidesXor) &&
+  if (SelectPatternResult::isMinOrMax(SPF1) &&
+      SelectPatternResult::isMinOrMax(SPF2) &&
+      IsFreeOrProfitableToInvert(A, NotA, ElidesXor) &&
       IsFreeOrProfitableToInvert(B, NotB, ElidesXor) &&
       IsFreeOrProfitableToInvert(C, NotC, ElidesXor) && ElidesXor) {
     if (!NotA)