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[WebAssembly] [Backend] Draft pull request for #129441 #145108

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badumbatish
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I'm hooking up dagcombine for AND(AND(AND(...), SHUFFLE(...)), SHUFFLE(...)) to reduce it to all_true.
I'm unsure why the hook for AND is not triggered when there are AND nodes as input to SelectionDAG. No nodes showed up as AND in:

SDValue
WebAssemblyTargetLowering::PerformDAGCombine(SDNode *N,
                                             DAGCombinerInfo &DCI) const {
  // N->print(llvm::errs());
  // std::cout << "\n";

llvm ir Godbolt link: https://godbolt.org/z/qYEvPn1KW

Local input to selection dag:

Initial selection DAG: %bb.0 'bar:entry'
SelectionDAG has 21 nodes:
          t2: v4i32 = WebAssemblyISD::ARGUMENT TargetConstant:i32<0>
        t3: v16i8 = bitcast t2
        t5: v16i8 = BUILD_VECTOR Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>
      t7: v16i1 = setcc t3, t5, setne:ch
    t8: v16i8 = sign_extend t7
  t9: v4i32 = bitcast t8
    t11: v4i32 = vector_shuffle<2,3,u,u> t9, poison:v4i32
  t12: v4i32 = and t9, t11
    t0: ch,glue = EntryToken
            t13: v4i32 = vector_shuffle<1,u,u,u> t12, poison:v4i32
          t14: v4i32 = and t12, t13
        t17: i32 = extract_vector_elt t14, Constant:i64<0>
      t18: i1 = setcc t17, Constant:i32<0>, setne:ch
    t19: i32 = zero_extend t18
  t20: ch = WebAssemblyISD::RETURN t0, t19



Combining: t20: ch = WebAssemblyISD::RETURN t0, t19

Combining: t19: i32 = zero_extend t18
Creating constant: t21: i1 = Constant<-1>
Creating constant: t22: i1 = Constant<0>

Combining: t18: i1 = setcc t17, Constant:i32<0>, setne:ch

Combining: t17: i32 = extract_vector_elt t14, Constant:i64<0>

Combining: t16: i64 = Constant<0>

Combining: t15: i32 = Constant<0>

Combining: t14: v4i32 = and t12, t13

Combining: t13: v4i32 = vector_shuffle<1,u,u,u> t12, poison:v4i32

Combining: t12: v4i32 = and t9, t11

Combining: t11: v4i32 = vector_shuffle<2,3,u,u> t9, poison:v4i32

Combining: t10: v4i32 = poison

Combining: t9: v4i32 = bitcast t8

Combining: t8: v16i8 = sign_extend t7
Creating new node: t23: v16i8 = setcc t3, t5, setne:ch
 ... into: t23: v16i8 = setcc t3, t5, setne:ch

Combining: t23: v16i8 = setcc t3, t5, setne:ch

Combining: t9: v4i32 = bitcast t23

Combining: t6: ch = setne

Combining: t5: v16i8 = BUILD_VECTOR Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>, Constant:i8<0>
Creating new node: t24: v16i8 = splat_vector Constant:i8<0>
 ... into: t24: v16i8 = splat_vector Constant:i8<0>

Combining: t24: v16i8 = splat_vector Constant:i8<0>

Combining: t23: v16i8 = setcc t3, t24, setne:ch

Combining: t4: i8 = Constant<0>

Combining: t3: v16i8 = bitcast t2

Combining: t2: v4i32 = WebAssemblyISD::ARGUMENT TargetConstant:i32<0>

Combining: t1: i32 = TargetConstant<0>

Combining: t0: ch,glue = EntryToken

Optimized lowered selection DAG: %bb.0 'bar:entry'
SelectionDAG has 20 nodes:
        t2: v4i32 = WebAssemblyISD::ARGUMENT TargetConstant:i32<0>
      t3: v16i8 = bitcast t2
      t24: v16i8 = splat_vector Constant:i8<0>
    t23: v16i8 = setcc t3, t24, setne:ch
  t9: v4i32 = bitcast t23
    t11: v4i32 = vector_shuffle<2,3,u,u> t9, poison:v4i32
  t12: v4i32 = and t9, t11
    t0: ch,glue = EntryToken
            t13: v4i32 = vector_shuffle<1,u,u,u> t12, poison:v4i32
          t14: v4i32 = and t12, t13
        t17: i32 = extract_vector_elt t14, Constant:i64<0>
      t18: i1 = setcc t17, Constant:i32<0>, setne:ch
    t19: i32 = zero_extend t18
  t20: ch = WebAssemblyISD::RETURN t0, t19

@badumbatish
Draft pull request for llvm#129441
86f26c1 
I'm hooking up dagcombine for AND(AND(AND(...), SHUFFLE(...)), SHUFFLE(...)) to reduce it to all_true.
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@badumbatish badumbatish changed the title Draft pull request for #129441 [WebAssembly] [Backend] Draft pull request for #129441 Jun 20, 2025
@lukel97
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lukel97 commented Jun 20, 2025

I'm unsure why the hook for AND is not triggered when there are AND nodes as input to SelectionDAG.

For the generic DAG nodes like ISD::AND you need to tell SelectionDAG that your target wants to perform custom combines on them by calling setTargetDAGCombine(ISD::AND); somewhere in the WebAssemblyTargetLowering constructor. Does that fix what you're seeing?

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