[llvm] r222604 - InstCombine: Preserve nsw for (mul %V, -1) -> (sub 0, %V)

[David Majnemer]

Author: majnemer
Date: Fri Nov 21 22:52:38 2014
New Revision: 222604

URL: http://llvm.org/viewvc/llvm-project?rev=222604&view=rev
Log:
InstCombine: Preserve nsw for (mul %V, -1) -> (sub 0, %V)

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
    llvm/trunk/test/Transforms/InstCombine/mul.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp?rev=222604&r1=222603&r2=222604&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp Fri Nov 21 22:52:38 2014
@@ -136,8 +136,13 @@ Instruction *InstCombiner::visitMul(Bina
   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.
   {

Modified: llvm/trunk/test/Transforms/InstCombine/mul.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/mul.ll?rev=222604&r1=222603&r2=222604&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/mul.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/mul.ll Fri Nov 21 22:52:38 2014
@@ -197,3 +197,10 @@ define <2 x i1> @test21(<2 x i1> %A, <2
         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
+}