[DAG] ABD is not reassociative

[dmgreen]

Summary

I'm not sure how I missed this in the testing, but as far as I understand whilst ABDS and ABDU are commutive they are not associative. This patch disables reassociateOps from visitABD, fixing the problems found in #61069.
ABDU: https://alive2.llvm.org/ce/z/eiT5QG
ABDS: https://alive2.llvm.org/ce/z/HzE29l

[RKSimon]

LGTM

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

SDValue DAGCombiner::visitABD(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
   EVT VT = N->getValueType(0);
   SDLoc DL(N);
 
   // fold (abd c1, c2)
   if (SDValue C = DAG.FoldConstantArithmetic(Opcode, DL, VT, {N0, N1}))
     return C;
-  // reassociate if possible
-  if (SDValue C = reassociateOps(Opcode, DL, N0, N1, N->getFlags()))
-    return C;
 
   // canonicalize constant to RHS.
   if (DAG.isConstantIntBuildVectorOrConstantInt(N0) &&
       !DAG.isConstantIntBuildVectorOrConstantInt(N1))
     return DAG.getNode(Opcode, DL, N->getVTList(), N1, N0);
 
   if (VT.isVector()) {
     if (SDValue FoldedVOp = SimplifyVBinOp(N, DL))

llvm/test/CodeGen/AArch64/abd-combine.ll

 ; CHECK-NEXT:    ret
   %result = call <8 x i16> @llvm.aarch64.neon.uabd.v8i16(<8 x i16> undef, <8 x i16> %src1)
   ret <8 x i16> %result
 }
 
 define <8 x i16> @abdu_i_reassoc(<8 x i16> %src1) {
 ; CHECK-LABEL: abdu_i_reassoc:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    movi v1.8h, #2
+; CHECK-NEXT:    movi v1.8h, #3
+; CHECK-NEXT:    movi v2.8h, #1
 ; CHECK-NEXT:    uabd v0.8h, v0.8h, v1.8h
+; CHECK-NEXT:    uabd v0.8h, v0.8h, v2.8h
 ; CHECK-NEXT:    ret
   %r1 = call <8 x i16> @llvm.aarch64.neon.uabd.v8i16(<8 x i16> %src1, <8 x i16> <i16 3, i16 3, i16 3, i16 3, i16 3, i16 3, i16 3, i16 3>)
   %result = call <8 x i16> @llvm.aarch64.neon.uabd.v8i16(<8 x i16> %r1, <8 x i16> <i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1>)
   ret <8 x i16> %result
 }
 
 
 

 ; CHECK-NEXT:    ret
   %result = call <8 x i16> @llvm.aarch64.neon.sabd.v8i16(<8 x i16> undef, <8 x i16> %src1)
   ret <8 x i16> %result
 }
 
 define <8 x i16> @abds_i_reassoc(<8 x i16> %src1) {
 ; CHECK-LABEL: abds_i_reassoc:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    movi v1.8h, #2
+; CHECK-NEXT:    movi v1.8h, #3
+; CHECK-NEXT:    movi v2.8h, #1
 ; CHECK-NEXT:    sabd v0.8h, v0.8h, v1.8h
+; CHECK-NEXT:    sabd v0.8h, v0.8h, v2.8h
 ; CHECK-NEXT:    ret
   %r1 = call <8 x i16> @llvm.aarch64.neon.sabd.v8i16(<8 x i16> %src1, <8 x i16> <i16 3, i16 3, i16 3, i16 3, i16 3, i16 3, i16 3, i16 3>)
   %result = call <8 x i16> @llvm.aarch64.neon.sabd.v8i16(<8 x i16> %r1, <8 x i16> <i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1>)
   ret <8 x i16> %result
 }
 
 
 declare <8 x i16> @llvm.aarch64.neon.uabd.v8i16(<8 x i16>, <8 x i16>)
 declare <8 x i16> @llvm.aarch64.neon.sabd.v8i16(<8 x i16>, <8 x i16>)
 declare <8 x i32> @llvm.abs.v8i32(<8 x i32>, i1)