InstCombine: Strength reduce sadd.with.overflow into a regular nsw add if we can prove that it cannot overflow.
PR20194
llvm-svn: 212331
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index ff74564..658178d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -421,6 +421,21 @@
return InsertValueInst::Create(Struct, II->getArgOperand(0), 0);
}
}
+
+ // We can strength reduce reduce this signed add into a regular add if we
+ // can prove that it will never overflow.
+ if (II->getIntrinsicID() == Intrinsic::sadd_with_overflow) {
+ Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
+ if (WillNotOverflowSignedAdd(LHS, RHS)) {
+ Value *Add = Builder->CreateNSWAdd(LHS, RHS);
+ Add->takeName(&CI);
+ Constant *V[] = {UndefValue::get(Add->getType()), Builder->getFalse()};
+ StructType *ST = cast<StructType>(II->getType());
+ Constant *Struct = ConstantStruct::get(ST, V);
+ return InsertValueInst::Create(Struct, Add, 0);
+ }
+ }
+
break;
case Intrinsic::usub_with_overflow:
case Intrinsic::ssub_with_overflow: