rdar://12329730 (defect 2)

Enhancement to InstCombine. Try to catch this opportunity:
  
 ---------------------------------------------------------------
 ((X^C1) >> C2) ^ C3  => (X>>C2) ^ ((C1>>C2)^C3)
  where the subexpression "X ^ C1" has more than one uses, and
  "(X^C1) >> C2" has single use. 
 ---------------------------------------------------------------- 

 Reviewed by Nadav (with minor change per his request).

llvm-svn: 168615

2 files changed, 36 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 494cc7d1517..12faedb0ffe 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2159,6 +2159,27 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
             I.setOperand(1, NewRHS);
             return &I;
           }
+        } else if (Op0I->getOpcode() == Instruction::LShr) {
+          // ((X^C1) >> C2) ^ C3 -> (X>>C2) ^ ((C1>>C2)^C3)
+          // E1 = "X ^ C1"
+          BinaryOperator *E1; 
+          ConstantInt *C1;
+          if (Op0I->hasOneUse() &&
+              (E1 = dyn_cast<BinaryOperator>(Op0I->getOperand(0))) &&
+              E1->getOpcode() == Instruction::Xor &&
+              (C1 = dyn_cast<ConstantInt>(E1->getOperand(1)))) {
+            // fold (C1 >> C2) ^ C3
+            ConstantInt *C2 = Op0CI, *C3 = RHS;
+            APInt FoldConst = C1->getValue().lshr(C2->getValue());
+            FoldConst ^= C3->getValue();
+            // Prepare the two operands.
+            Value *Opnd0 = Builder->CreateLShr(E1->getOperand(0), C2);
+            Opnd0->takeName(Op0I);
+            cast<Instruction>(Opnd0)->setDebugLoc(I.getDebugLoc());
+            Value *FoldVal = ConstantInt::get(Opnd0->getType(), FoldConst);
+
+            return BinaryOperator::CreateXor(Opnd0, FoldVal);
+          }
         }
       }
     }
diff --git a/llvm/test/Transforms/InstCombine/xor2.ll b/llvm/test/Transforms/InstCombine/xor2.ll
index 89f00bd6847..3c992467967 100644
--- a/llvm/test/Transforms/InstCombine/xor2.ll
+++ b/llvm/test/Transforms/InstCombine/xor2.ll
@@ -51,3 +51,18 @@ define i32 @test4(i32 %A, i32 %B) {
 ; CHECK: %1 = ashr i32 %A, %B
 ; CHECK: ret i32 %1
 }
+
+; defect-2 in rdar://12329730
+; (X^C1) >> C2) ^ C3 -> (X>>C2) ^ ((C1>>C2)^C3)
+;   where the "X" has more than one use
+define i32 @test5(i32 %val1) {
+test5:
+  %xor = xor i32 %val1, 1234
+  %shr = lshr i32 %xor, 8
+  %xor1 = xor i32 %shr, 1
+  %add = add i32 %xor1, %xor
+  ret i32 %add
+; CHECK: @test5
+; CHECK: lshr i32 %val1, 8
+; CHECK: ret
+}