[InstSimplify] Optimize away udivs in the presence of range metadata

We know that udiv %V, C can be optimized away to 0 if %V is ult C.

llvm-svn: 291296

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 7ae7c4ef939..8da2f0981d0 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1106,6 +1106,16 @@ static Value *SimplifyUDivInst(Value *Op0, Value *Op1, const Query &Q,
   if (Value *V = SimplifyDiv(Instruction::UDiv, Op0, Op1, Q, MaxRecurse))
     return V;
 
+  // udiv %V, C -> 0 if %V < C
+  if (MaxRecurse) {
+    if (Constant *C = dyn_cast_or_null<Constant>(SimplifyICmpInst(
+            ICmpInst::ICMP_ULT, Op0, Op1, Q, MaxRecurse - 1))) {
+      if (C->isAllOnesValue()) {
+        return Constant::getNullValue(Op0->getType());
+      }
+    }
+  }
+
   return nullptr;
 }