[DAG] Refactor X86 combineVSelectWithAllOnesOrZeros fold into a generic DAG Combine

[RKSimon]

combineVSelectWithAllOnesOrZeros folds vselect(cond, 0/-1, X) and vselect(cond, X, 0/-1) style patterns into logic operations when the cond is the same width and ZeroOrNegativeOneBooleanContent

We should be able to perform this generically in DAGCombiner (with suitable freezing which seems to be missing from the x86 version)

[RKSimon]

CC @woruyu - not sure if you'd want to take this on but its not dissimilar to the foldMaskedMerge patches you've tried in the past.

[woruyu]

@RKSimon , of course，I'm glad to, thank you!

[woruyu]

hello, @RKSimon , I meet a proble, the code is

static SDValue
combineVSelectWithAllOnesOrZeros(SDValue Cond, SDValue TVal, SDValue FVal,const TargetLowering &TLI,
                                  SelectionDAG &DAG, const SDLoc &DL) {
.............

  // select Cond, 0, x → andn Cond, x = (~Cond) & x
  if (IsTAllZero && TLI.hasAndNot(Cond)) {
    SDValue X = DAG.getBitcast(CondVT, FVal);
    SDValue NotCond = DAG.getNOT(DL, Cond, CondVT);
    SDValue AndN = DAG.getNode(ISD::AND, DL, CondVT, NotCond, X);
    return DAG.getBitcast(VT, AndN);


    // SDValue CastRHS = DAG.getBitcast(CondVT, FVal);
    // SDValue AndN;
    // // The canonical form differs for i1 vectors - x86andnp is not used
    // if (CondVT.getScalarType() == MVT::i1){
    //   AndN = DAG.getNode(ISD::AND, DL, CondVT, DAG.getNOT(DL, Cond, CondVT),
    //                      CastRHS);
    //   llvm_unreachable("woruyu");
    // }
    // else
    //   AndN = DAG.getNode(556, DL, CondVT, Cond, CastRHS);
    // return DAG.getBitcast(VT, AndN);
  }

  return SDValue();
}

for this pattern select Cond, 0, x → andn Cond, x = (~Cond) & x, in DAGCombine, it is translated to And + xor instead of andnot, so I run ninja check-llvm-codegen-x86,An error occurred，diff like this

I want to ask to confirm whether I need to add (~Cond) & x -> andn Cond, x to x86 backned Or any other idea?

[woruyu]

Added pr

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

combineVSelectWithAllOnesOrZeros folds `vselect(cond, 0/-1, X)` and `vselect(cond, X, 0/-1)` style patterns into logic operations when the cond is the same width and ZeroOrNegativeOneBooleanContent

We should be able to perform this generically in DAGCombiner (with suitable freezing which seems to be missing from the x86 version)