[llvm] r326660 - [InstCombine] (~X) - (~Y) --> Y - X

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Sat Mar  3 09:53:25 2018
New Revision: 326660

URL: http://llvm.org/viewvc/llvm-project?rev=326660&view=rev
Log:
[InstCombine] (~X) - (~Y) --> Y - X

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    llvm/trunk/test/Transforms/InstCombine/sub.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp?rev=326660&r1=326659&r2=326660&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp Sat Mar  3 09:53:25 2018
@@ -1511,6 +1511,11 @@ Instruction *InstCombiner::visitSub(Bina
   if (match(Op0, m_AllOnes()))
     return BinaryOperator::CreateNot(Op1);
 
+  // (~X) - (~Y) --> Y - X
+  Value *X, *Y;
+  if (match(Op0, m_Not(m_Value(X))) && match(Op1, m_Not(m_Value(Y))))
+    return BinaryOperator::CreateSub(Y, X);
+
   if (Constant *C = dyn_cast<Constant>(Op0)) {
     Value *X;
     // C - zext(bool) -> bool ? C - 1 : C

Modified: llvm/trunk/test/Transforms/InstCombine/sub.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/sub.ll?rev=326660&r1=326659&r2=326660&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/sub.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/sub.ll Sat Mar  3 09:53:25 2018
@@ -50,7 +50,7 @@ define i8 @notnotsub(i8 %x, i8 %y) {
 ; CHECK-LABEL: @notnotsub(
 ; CHECK-NEXT:    [[NX:%.*]] = xor i8 [[X:%.*]], -1
 ; CHECK-NEXT:    [[NY:%.*]] = xor i8 [[Y:%.*]], -1
-; CHECK-NEXT:    [[SUB:%.*]] = sub i8 [[NX]], [[NY]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub i8 [[Y]], [[X]]
 ; CHECK-NEXT:    call void @use8(i8 [[NX]])
 ; CHECK-NEXT:    call void @use8(i8 [[NY]])
 ; CHECK-NEXT:    ret i8 [[SUB]]
@@ -65,9 +65,7 @@ define i8 @notnotsub(i8 %x, i8 %y) {
 
 define <2 x i8> @notnotsub_vec(<2 x i8> %x, <2 x i8> %y) {
 ; CHECK-LABEL: @notnotsub_vec(
-; CHECK-NEXT:    [[NX:%.*]] = xor <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
-; CHECK-NEXT:    [[NY:%.*]] = xor <2 x i8> [[Y:%.*]], <i8 -1, i8 -1>
-; CHECK-NEXT:    [[SUB:%.*]] = sub <2 x i8> [[NX]], [[NY]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub <2 x i8> [[Y:%.*]], [[X:%.*]]
 ; CHECK-NEXT:    ret <2 x i8> [[SUB]]
 ;
   %nx = xor <2 x i8> %x, <i8 -1, i8 -1>