[InstCombine] Fold (C - X) ^ signmask -> (C + signmask - X).

llvm-svn: 310186

1 files changed, 11 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index a3749a1581b..7b32812a2c1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2422,11 +2422,17 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
   if (ConstantInt *RHSC = dyn_cast<ConstantInt>(Op1)) {
     if (BinaryOperator *Op0I = dyn_cast<BinaryOperator>(Op0)) {
       // ~(c-X) == X-c-1 == X+(-c-1)
-      if (Op0I->getOpcode() == Instruction::Sub && RHSC->isMinusOne())
-        if (Constant *Op0I0C = dyn_cast<Constant>(Op0I->getOperand(0))) {
-          Constant *NegOp0I0C = ConstantExpr::getNeg(Op0I0C);
-          return BinaryOperator::CreateAdd(Op0I->getOperand(1),
-                                           SubOne(NegOp0I0C));
+      if (Op0I->getOpcode() == Instruction::Sub)
+        if (ConstantInt *Op0I0C = dyn_cast<ConstantInt>(Op0I->getOperand(0))) {
+          if (RHSC->isMinusOne()) {
+            Constant *NegOp0I0C = ConstantExpr::getNeg(Op0I0C);
+            return BinaryOperator::CreateAdd(Op0I->getOperand(1),
+                                             SubOne(NegOp0I0C));
+          } else if (RHSC->getValue().isSignMask()) {
+            // (C - X) ^ signmask -> (C + signmask - X)
+            Constant *C = Builder.getInt(RHSC->getValue() + Op0I0C->getValue());
+            return BinaryOperator::CreateSub(C, Op0I->getOperand(1));
+          }
         }
 
       if (ConstantInt *Op0CI = dyn_cast<ConstantInt>(Op0I->getOperand(1))) {
@@ -2440,7 +2446,6 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
             // (X + C) ^ signmask -> (X + C + signmask)
             Constant *C = Builder.getInt(RHSC->getValue() + Op0CI->getValue());
             return BinaryOperator::CreateAdd(Op0I->getOperand(0), C);
-
           }
         } else if (Op0I->getOpcode() == Instruction::Or) {
           // (X|C1)^C2 -> X^(C1|C2) iff X&~C1 == 0