InstCombine: Strength reduce sadd.with.overflow into a regular nsw add if we can...

[oota-llvm.git] / lib / Transforms / InstCombine / InstCombineCalls.cpp

diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp
index ff745641581455299acb5c2eba6414ce9fd3611d..658178d5914ebc38fd6f875c6d22ead89e598a7e 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -421,6 +421,21 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
         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: