[llvm] r181249 - InstCombine: (X ^ signbit) + C -> X + (signbit ^ C)

[David Majnemer]

Author: majnemer
Date: Mon May  6 16:21:31 2013
New Revision: 181249

URL: http://llvm.org/viewvc/llvm-project?rev=181249&view=rev
Log:
InstCombine: (X ^ signbit) + C -> X + (signbit ^ C)

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

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp?rev=181249&r1=181248&r2=181249&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp Mon May  6 16:21:31 2013
@@ -974,6 +974,11 @@ Instruction *InstCombiner::visitAdd(Bina
           return BinaryOperator::CreateSub(ConstantExpr::getAdd(XorRHS, CI),
                                            XorLHS);
       }
+      // (X + signbit) + C could have gotten canonicalized to (X ^ signbit) + C,
+      // transform them into (X + (signbit ^ C))
+      if (XorRHS->getValue().isSignBit())
+          return BinaryOperator::CreateAdd(XorLHS,
+                                           ConstantExpr::getXor(XorRHS, CI));
     }
   }
 

Modified: llvm/trunk/test/Transforms/InstCombine/sub-xor.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/sub-xor.ll?rev=181249&r1=181248&r2=181249&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/sub-xor.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/sub-xor.ll Mon May  6 16:21:31 2013
@@ -35,3 +35,13 @@ define i32 @test3(i32 %x) nounwind {
 ; CHECK-NEXT: sub i32 73, %and
 ; CHECK-NEXT: ret
 }
+
+define i32 @test4(i32 %x) nounwind {
+  %sub = xor i32 %x, 2147483648
+  %add = add i32 %sub, 42
+  ret i32 %add
+
+; CHECK: @test4
+; CHECK-NEXT: add i32 %x, -2147483606
+; CHECK-NEXT: ret
+}