[PATCH] D145064: [DAG] ABD is not reassociative

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: RKSimon, ilinpv.
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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


https://reviews.llvm.org/D145064

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/AArch64/abd-combine.ll


Index: llvm/test/CodeGen/AArch64/abd-combine.ll
===================================================================
--- llvm/test/CodeGen/AArch64/abd-combine.ll
+++ llvm/test/CodeGen/AArch64/abd-combine.ll
@@ -321,8 +321,10 @@
 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>)
@@ -539,8 +541,10 @@
 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>)
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5073,9 +5073,6 @@
   // 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) &&


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