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[DAG] Fold (and X, (bswap/bitreverse (not Y))) -> (and X, (not (bswap/bitreverse Y))) #112547

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Merged
merged 3 commits into from
Oct 28, 2024
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[DAG] Fold (and X, (bswap/bitreverse (not Y))) -> (and X, (not (bswap/bitreverse Y))) #112547

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[DAG] Fold (and X, (bswap/bitreverse (not Y))) -> (and X, (not (bswap…
RKSimon Oct 16, 2024
9ba8f81
[X86] andnot-patterns.ll - add additional multiuse tests
RKSimon Oct 18, 2024
77adbb3
Relax ANDNOT requirement to be only for multiple uses of the NOT
RKSimon Oct 18, 2024
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11 changes: 11 additions & 0 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7353,6 +7353,17 @@ SDValue DAGCombiner::visitAND(SDNode *N) {
if (SDValue R = foldLogicOfShifts(N, N1, N0, DAG))
return R;

// Fold (and X, (bswap (not Y))) -> (and X, (not (bswap Y)))
// Fold (and X, (bitreverse (not Y))) -> (and X, (not (bitreverse Y)))
SDValue X, Y, NotY;
for (unsigned Opc : {ISD::BSWAP, ISD::BITREVERSE})
if (sd_match(N,
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@goldsteinn goldsteinn Oct 18, 2024

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Maybe should be || (NotY->hasOneUse() && sd_match(X, m_Not(m_Value()))

There is a lot of diff from just re-assosiating the not which seems netural.

No strong opinion, however.

m_And(m_Value(X), m_OneUse(m_UnaryOp(Opc, m_Value(NotY))))) &&
sd_match(NotY, m_Not(m_Value(Y))) &&
(TLI.hasAndNot(SDValue(N, 0)) || NotY->hasOneUse()))
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@goldsteinn goldsteinn Oct 16, 2024

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Is this necessary? Seems like it expose ~X & ~Y -> ~(X | Y)

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@dtcxzyw dtcxzyw Oct 16, 2024

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It is ~X & bitreverse/bswap(~Y).

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@RKSimon RKSimon Oct 16, 2024

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Yes - its to prevent the fold when we already have a ANDNOT pattern.

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@goldsteinn goldsteinn Oct 16, 2024

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I mean isn't ~X & bitreverse/bswap(~Y) -> ~X & ~bitreverse/bswap(Y) also profitable? Irrelivant of ANDNOT in fact.

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@goldsteinn goldsteinn Oct 16, 2024

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I guess assuming ~Y is one-use.

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@RKSimon RKSimon Oct 16, 2024

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Yes, for the NOT(Y) we can allow multiple uses as with a ANDNOT we'll be getting it for free - I'd be willing to allow this fold to occur on targets without ANDNOT, if for those targets we require the NOT(Y) to have one use?

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@goldsteinn goldsteinn Oct 16, 2024

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Yeah, something like

if (sd_match(N, m_And(m_Value(X),
                            m_OneUse(m_UnaryOp(Opc, m_Value(NotY)))) &&
   match(NotY, m_Not(m_Value(Y))) && (TLI.hasAndNot(SDValue(N, 0) || NotY->hasOneUse())

should work.

return DAG.getNode(ISD::AND, DL, VT, X,
DAG.getNOT(DL, DAG.getNode(Opc, DL, VT, Y), VT));

// Masking the negated extension of a boolean is just the zero-extended
// boolean:
// and (sub 0, zext(bool X)), 1 --> zext(bool X)
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