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SIGN_EXTEND_INREG does not demand its top bits. Give SimplifyDemandedBits

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a chance to hack on it.  This compiles:

int baz(long long a) { return (short)(((int)(a >>24)) >> 9); }

into:
_baz:
        slwi r2, r3, 8
        srwi r2, r2, 9
        extsh r3, r2
        blr

instead of:

_baz:
        srwi r2, r4, 24
        rlwimi r2, r3, 8, 0, 23
        srwi r2, r2, 9
        extsh r3, r2
        blr

This implements CodeGen/PowerPC/sign_ext_inreg1.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36212 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-04-17 19:03:21 +00:00
parent 84e8315aaa
commit 95a5e0507e
1 changed files with 6 additions and 1 deletions
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7
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -2429,10 +2429,15 @@ SDOperand DAGCombiner::visitSIGN_EXTEND_INREG(SDNode *N) {
return DAG.getNode(ISD::SIGN_EXTEND_INREG, VT, N0.getOperand(0), N1);
}
// fold (sext_in_reg x) -> (zext_in_reg x) if the sign bit is zero
// fold (sext_in_reg x) -> (zext_in_reg x) if the sign bit is known zero.
if (TLI.MaskedValueIsZero(N0, 1ULL << (EVTBits-1)))
return DAG.getZeroExtendInReg(N0, EVT);
// fold operands of sext_in_reg based on knowledge that the top bits are not
// demanded.
if (SimplifyDemandedBits(SDOperand(N, 0)))
return SDOperand(N, 0);
// fold (sext_in_reg (load x)) -> (smaller sextload x)
// fold (sext_in_reg (srl (load x), c)) -> (smaller sextload (x+c/evtbits))
SDOperand NarrowLoad = ReduceLoadWidth(N);