InstCombine: Preserve nsw for (mul %V, -1) -> (sub 0, %V)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222604 91177308-0d34-0410-b5e6-96231b3b80d8
bgamari · Nov 22, 2014 · 0f89917 · 0f89917
1 parent 5182ad5
commit 0f89917
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Showing 2 changed files with 14 additions and 2 deletions.
diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -136,8 +136,13 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
   if (Value *V = SimplifyUsingDistributiveLaws(I))
     return ReplaceInstUsesWith(I, V);
 
-  if (match(Op1, m_AllOnes()))  // X * -1 == 0 - X
-    return BinaryOperator::CreateNeg(Op0, I.getName());
+  // X * -1 == 0 - X
+  if (match(Op1, m_AllOnes())) {
+    BinaryOperator *BO = BinaryOperator::CreateNeg(Op0, I.getName());
+    if (I.hasNoSignedWrap())
+      BO->setHasNoSignedWrap();
+    return BO;
+  }
 
   // Also allow combining multiply instructions on vectors.
   {

diff --git a/test/Transforms/InstCombine/mul.ll b/test/Transforms/InstCombine/mul.ll
@@ -197,3 +197,10 @@ define <2 x i1> @test21(<2 x i1> %A, <2 x i1> %B) {
         ret <2 x i1> %C
 ; CHECK: %C = and <2 x i1> %A, %B
 }
+
+define i32 @test22(i32 %A) {
+; CHECK-LABEL: @test22(
+        %B = mul nsw i32 %A, -1
+        ret i32 %B
+; CHECK: sub nsw i32 0, %A
+}