if a 'with overflow' intrinsic just has the normal result used, simplify

it to a normal binop.  Patch by Alastair Lynn, testcase by me.

llvm-svn: 86524

2 files changed, 53 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 6e9324f9ebb..52b9b0438f3 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -12452,6 +12452,47 @@ Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {
       return ExtractValueInst::Create(IV->getInsertedValueOperand(), 
                                       exti, exte);
   }
+  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Agg)) {
+    // We're extracting from an intrinsic, see if we're the only user, which
+    // allows us to simplify multiple result intrinsics to simpler things that
+    // just get one value..
+    if (II->hasOneUse()) {
+      // Check if we're grabbing the overflow bit or the result of a 'with
+      // overflow' intrinsic.  If it's the latter we can remove the intrinsic
+      // and replace it with a traditional binary instruction.
+      switch (II->getIntrinsicID()) {
+      case Intrinsic::uadd_with_overflow:
+      case Intrinsic::sadd_with_overflow:
+        if (*EV.idx_begin() == 0) {  // Normal result.
+          Value *LHS = II->getOperand(1), *RHS = II->getOperand(2);
+          II->replaceAllUsesWith(UndefValue::get(II->getType()));
+          EraseInstFromFunction(*II);
+          return BinaryOperator::CreateAdd(LHS, RHS);
+        }
+        break;
+      case Intrinsic::usub_with_overflow:
+      case Intrinsic::ssub_with_overflow:
+        if (*EV.idx_begin() == 0) {  // Normal result.
+          Value *LHS = II->getOperand(1), *RHS = II->getOperand(2);
+          II->replaceAllUsesWith(UndefValue::get(II->getType()));
+          EraseInstFromFunction(*II);
+          return BinaryOperator::CreateSub(LHS, RHS);
+        }
+        break;
+      case Intrinsic::umul_with_overflow:
+      case Intrinsic::smul_with_overflow:
+        if (*EV.idx_begin() == 0) {  // Normal result.
+          Value *LHS = II->getOperand(1), *RHS = II->getOperand(2);
+          II->replaceAllUsesWith(UndefValue::get(II->getType()));
+          EraseInstFromFunction(*II);
+          return BinaryOperator::CreateMul(LHS, RHS);
+        }
+        break;
+      default:
+        break;
+      }
+    }
+  }
   // Can't simplify extracts from other values. Note that nested extracts are
   // already simplified implicitely by the above (extract ( extract (insert) )
   // will be translated into extract ( insert ( extract ) ) first and then just
diff --git a/llvm/test/Transforms/InstCombine/intrinsics.ll b/llvm/test/Transforms/InstCombine/intrinsics.ll
new file mode 100644
index 00000000000..7abd3804013
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/intrinsics.ll
@@ -0,0 +1,12 @@
+; RUN: opt %s -instcombine -S | FileCheck %s
+
+declare {i8, i1} @llvm.uadd.with.overflow.i8(i8, i8)
+
+define i8 @test1(i8 %A, i8 %B) {
+  %x = call {i8, i1} @llvm.uadd.with.overflow.i8(i8 %A, i8 %B)
+  %y = extractvalue  {i8, i1} %x, 0
+  ret i8 %y
+; CHECK: @test1
+; CHECK-NEXT: %y = add i8 %A, %B
+; CHECK-NEXT: ret i8 %y
+}