[PATCH 1/1] DAGCombiner: Add (A - (0-B)) -> A+B optimization

[Chad Rosier]

Testcase?

> Signed-off-by: Jan Vesely <jan.vesely at rutgers.edu>
> ---
>  lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> index 33e7059..bc39fe3 100644
> --- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> +++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> @@ -1794,6 +1794,10 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
>    // fold (A+B)-B -> A
>    if (N0.getOpcode() == ISD::ADD && N0.getOperand(1) == N1)
>      return N0.getOperand(0);
> +  // fold (A - (0-B)) -> A+B
> +  if (N1.getOpcode() == ISD::SUB && isa<ConstantSDNode>(N1.getOperand(0))
> &&
> +      cast<ConstantSDNode>(N1.getOperand(0))->isNullValue())
> +    return DAG.getNode(ISD::ADD, SDLoc(N), VT, N0, N1.getOperand(1));
>    // fold C2-(A+C1) -> (C2-C1)-A
>    if (N1.getOpcode() == ISD::ADD && N0C && N1C1) {
>      SDValue NewC = DAG.getConstant(N0C->getAPIntValue() -
> N1C1->getAPIntValue(),
> --
> 1.9.3
>
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