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Disable the (A == (B-A)) -> 2*A == B xform when the sub has multiple uses (in

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this case, the xform introduces an extra operation).  This compiles
PowerPC/compare-duplicate.ll into:

_test:
        subf r2, r3, r4
        cmplw cr0, r2, r3
        bne cr0, LBB1_2 ;F

instead of:

_test:
        slwi r2, r3, 1
        subf r3, r3, r4
        cmplw cr0, r4, r2
        bne cr0, LBB1_2 ;F

This is target independent of course.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37246 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-05-19 00:43:44 +00:00
parent 35fbae2b6d
commit 2ad913b342
1 changed files with 1 additions and 1 deletions
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2
lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -1785,7 +1785,7 @@ TargetLowering::SimplifySetCC(MVT::ValueType VT, SDOperand N0, SDOperand N1,
if (DAG.isCommutativeBinOp(N0.getOpcode())) if (DAG.isCommutativeBinOp(N0.getOpcode()))
return DAG.getSetCC(VT, N0.getOperand(0), return DAG.getSetCC(VT, N0.getOperand(0),
DAG.getConstant(0, N0.getValueType()), Cond); DAG.getConstant(0, N0.getValueType()), Cond);
else { else if (N0.Val->hasOneUse()) {
assert(N0.getOpcode() == ISD::SUB && "Unexpected operation!"); assert(N0.getOpcode() == ISD::SUB && "Unexpected operation!");
// (Z-X) == X --> Z == X<<1 // (Z-X) == X --> Z == X<<1
SDOperand SH = DAG.getNode(ISD::SHL, N1.getValueType(), SDOperand SH = DAG.getNode(ISD::SHL, N1.getValueType(),