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Fold (add x, shl(0 - y, n)) -> sub(x, shl(y, n)), to simplify some code

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that SCEVExpander can produce when running on behalf of LSR.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93949 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2010-01-19 23:30:49 +00:00
parent cb9a6aab02
commit cd9e155755
2 changed files with 37 additions and 0 deletions
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lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+20
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@@ -1088,6 +1088,26 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
if (Result.getNode()) return Result;
}
// fold (add x, shl(0 - y, n)) -> sub(x, shl(y, n))
if (N1.getOpcode() == ISD::SHL &&
N1.getOperand(0).getOpcode() == ISD::SUB)
if (ConstantSDNode *C =
dyn_cast<ConstantSDNode>(N1.getOperand(0).getOperand(0)))
if (C->getAPIntValue() == 0)
return DAG.getNode(ISD::SUB, N->getDebugLoc(), VT, N0,
DAG.getNode(ISD::SHL, N->getDebugLoc(), VT,
N1.getOperand(0).getOperand(1),
N1.getOperand(1)));
if (N0.getOpcode() == ISD::SHL &&
N0.getOperand(0).getOpcode() == ISD::SUB)
if (ConstantSDNode *C =
dyn_cast<ConstantSDNode>(N0.getOperand(0).getOperand(0)))
if (C->getAPIntValue() == 0)
return DAG.getNode(ISD::SUB, N->getDebugLoc(), VT, N1,
DAG.getNode(ISD::SHL, N->getDebugLoc(), VT,
N0.getOperand(0).getOperand(1),
N0.getOperand(1)));
return SDValue();
}