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Use the new TargetLowering::ComputeNumSignBits method to eliminate

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sign_extend_inreg operations.  Though ComputeNumSignBits is still rudimentary,
this is enough to compile this:

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

into:

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

instead of:

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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28146 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-05-06 09:30:03 +00:00
parent 5c3e21d687
commit ee4ea92358
1 changed files with 5 additions and 5 deletions
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10
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -1937,6 +1937,11 @@ SDOperand DAGCombiner::visitSIGN_EXTEND_INREG(SDNode *N) {
SDOperand Truncate = DAG.getConstant(N0C->getValue(), EVT);
return DAG.getNode(ISD::SIGN_EXTEND, VT, Truncate);
}
// If the input is already sign extended, just drop the extend.
if (TLI.ComputeNumSignBits(N0) >= MVT::getSizeInBits(VT)-EVTBits+1)
return N0;
// fold (sext_in_reg (sext_in_reg x, VT2), VT1) -> (sext_in_reg x, minVT) pt1
if (N0.getOpcode() == ISD::SIGN_EXTEND_INREG &&
cast<VTSDNode>(N0.getOperand(1))->getVT() <= EVT) {
@ -1947,11 +1952,6 @@ 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 (assert_sext x)) -> (assert_sext x)
if (N0.getOpcode() == ISD::AssertSext &&
cast<VTSDNode>(N0.getOperand(1))->getVT() <= EVT) {
return N0;
}
// fold (sext_in_reg (sextload x)) -> (sextload x)
if (N0.getOpcode() == ISD::SEXTLOAD &&
cast<VTSDNode>(N0.getOperand(3))->getVT() <= EVT) {