[InstCombine] foldUnsignedUnderflowCheck(): one last pattern with 'sub' (PR43251)

https://rise4fun.com/Alive/0j9

llvm-svn: 372930

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 6252e5d15a1..db5095b6fea 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1128,6 +1128,16 @@ static Value *foldUnsignedUnderflowCheck(ICmpInst *ZeroICmp,
       EqPred == ICmpInst::ICMP_EQ && !IsAnd)
     return Builder.CreateICmpULE(Base, Offset);
 
+  // Base <= Offset && (Base - Offset) != 0  -->  Base < Offset
+  if (UnsignedPred == ICmpInst::ICMP_ULE && EqPred == ICmpInst::ICMP_NE &&
+      IsAnd)
+    return Builder.CreateICmpULT(Base, Offset);
+
+  // Base > Offset || (Base - Offset) == 0  -->  Base >= Offset
+  if (UnsignedPred == ICmpInst::ICMP_UGT && EqPred == ICmpInst::ICMP_EQ &&
+      !IsAnd)
+    return Builder.CreateICmpUGE(Base, Offset);
+
   return nullptr;
 }