[InstSimplify] Simplify uadd/sadd/umul/smul with overflow intrinsics when the Zero or Undef is on the LHS.

Summary: This code was migrated from InstCombine a few years ago. InstCombine had nearby code that would move Constants to the RHS for these, but InstSimplify doesn't have such code on this path.

Reviewers: spatel, majnemer, davide

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33473

llvm-svn: 303774

1 files changed, 5 insertions, 3 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 9572d81e471..f10e2378fdb 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4440,19 +4440,21 @@ static Value *SimplifyIntrinsic(Function *F, IterTy ArgBegin, IterTy ArgEnd,
     case Intrinsic::uadd_with_overflow:
     case Intrinsic::sadd_with_overflow: {
       // X + undef -> undef
-      if (isa<UndefValue>(RHS))
+      if (isa<UndefValue>(LHS) || isa<UndefValue>(RHS))
         return UndefValue::get(ReturnType);
 
       return nullptr;
     }
     case Intrinsic::umul_with_overflow:
     case Intrinsic::smul_with_overflow: {
+      // 0 * X -> { 0, false }
       // X * 0 -> { 0, false }
-      if (match(RHS, m_Zero()))
+      if (match(LHS, m_Zero()) || match(RHS, m_Zero()))
         return Constant::getNullValue(ReturnType);
 
+      // undef * X -> { 0, false }
       // X * undef -> { 0, false }
-      if (match(RHS, m_Undef()))
+      if (match(LHS, m_Undef()) || match(RHS, m_Undef()))
         return Constant::getNullValue(ReturnType);
 
       return nullptr;