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Make the case I just checked in stronger. Now we compile this:

Browse Source 
short test2(short X, short x) {
  int Y = (short)(X+x);
  return Y >> 1;
}

to:

_test2:
        add r2, r3, r4
        extsh r2, r2
        srawi r3, r2, 1
        blr

instead of:

_test2:
        add r2, r3, r4
        extsh r2, r2
        srwi r2, r2, 1
        extsh r3, r2
        blr

llvm-svn: 28175
This commit is contained in:
Chris Lattner 2006-05-08 21:18:59 +00:00
parent 7b8a0cfff3
commit eed10e837c
1 changed files with 16 additions and 8 deletions

24
lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@ -1948,17 +1948,25 @@ SDOperand DAGCombiner::visitSIGN_EXTEND_INREG(SDNode *N) {
EVT < cast<VTSDNode>(N0.getOperand(1))->getVT()) {
return DAG.getNode(ISD::SIGN_EXTEND_INREG, VT, N0.getOperand(0), N1);
}
// fold (sext_in_reg (srl X, 24), i8) -> sra X, 24
if (N0.getOpcode() == ISD::SRL) {
if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(N0.getOperand(1)))
if (ShAmt->getValue()+EVTBits == MVT::getSizeInBits(VT))
return DAG.getNode(ISD::SRA, VT, N0.getOperand(0), N0.getOperand(1));
}
// fold (sext_in_reg x) -> (zext_in_reg x) if the sign bit is zero
if (TLI.MaskedValueIsZero(N0, 1ULL << (EVTBits-1)))
return DAG.getZeroExtendInReg(N0, EVT);
// fold (sext_in_reg (srl X, 24), i8) -> sra X, 24
// fold (sext_in_reg (srl X, 23), i8) -> sra X, 23 iff possible.
// We already fold "(sext_in_reg (srl X, 25), i8) -> srl X, 25" above.
if (N0.getOpcode() == ISD::SRL) {
if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(N0.getOperand(1)))
if (ShAmt->getValue()+EVTBits <= MVT::getSizeInBits(VT)) {
// We can turn this into an SRA iff the input to the SRL is already sign
// extended enough.
unsigned InSignBits = TLI.ComputeNumSignBits(N0.getOperand(0));
if (MVT::getSizeInBits(VT)-(ShAmt->getValue()+EVTBits) < InSignBits)
return DAG.getNode(ISD::SRA, VT, N0.getOperand(0), N0.getOperand(1));
}
}
// fold (sext_inreg (extload x)) -> (sextload x)
if (N0.getOpcode() == ISD::EXTLOAD &&
EVT == cast<VTSDNode>(N0.getOperand(3))->getVT() &&