[InstCombine] fold X == 0 || X == -1 to one compare (PR32524)

This is effectively a retry of:
https://reviews.llvm.org/rL299851
but now we have tests and an assert to make sure the bug
that was exposed with that attempt will not happen again.

I'll fix the code duplication and missing sibling fold next,
but I want to make this change as small as possible to reduce
risk since I messed it up last time.

This should fix:
https://bugs.llvm.org/show_bug.cgi?id=32524

llvm-svn: 300236

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index efe1c068300..a661156f4ca 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -878,7 +878,7 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
       return RHS;
     case ICmpInst::ICMP_NE:
       // Special case to get the ordering right when the values wrap around
-      // zero.
+      // zero. Ie, we assumed the constants were unsigned when swapping earlier.
       if (LHSC->getValue() == 0 && RHSC->getValue().isAllOnesValue())
         std::swap(LHSC, RHSC);
       if (LHSC == SubOne(RHSC)) {
@@ -1785,6 +1785,10 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
         }
       }
 
+      // Special case to get the ordering right when the values wrap around
+      // zero. Ie, we assumed the constants were unsigned when swapping earlier.
+      if (LHSC->getValue() == 0 && RHSC->getValue().isAllOnesValue())
+        std::swap(LHSC, RHSC);
       if (LHSC == SubOne(RHSC)) {
         // (X == 13 | X == 14) -> X-13 <=u 1
         // An 'add' is the canonical IR form, so favor that over a 'sub'.