[SLPVectorizer] Fix crash in vectorizeChainsInBlock for scalable vector.

[CarolineConcatto]

Summary

The function vectorizeChainsInBlock does not support scalable vector,
because function like canReuseExtract and isCommutative in the code
path assert with scalable vectors.

This patch avoids vectorizing blocks that have instructions with scalable vector
or when the block uses operands from outside the block that are
scalable vector.

[ABataev]

I think it is better to change buildTree_rec function and check that if S.getOpcode() == Instruction::ExtractElement && cast<ExtractElementInst>(S.getMainOp())->getVectorOperandType()->isScalalableVectorType() then make it a gather node. Also, need to update getEntryCost function to filter out such extractelements from isGatherShuffledEntry function call and consider them as just simple gathers.

[CarolineConcatto]

• Remove the generic approach for scalable vector
• Use gather node for extract instructions with scalable vector

[CarolineConcatto]

@ABataev I try to follow your suggestion.
I could not find a test that could fail without a extract instruction.
So I followed your suggestion.
The previous one implemented was more generic.
What is done in getEntryCost is what you had in mind for the cost when it is an extract instruction?

[ABataev]

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

2682

cast<ExtractElementInst>(S.OpValue)->getVectorOperandType()

3750–3752

I would just add a check here && !isa<ScalableVectorType>(cast<ExtractElementInst>(E->getMainOp())->getVectorOperandType()) and drop changes in lines 3754-3760

3760

No need to call it again, it is called already in line 3721

[CarolineConcatto]

-Remove redundant code in getEntryCost

[CarolineConcatto]

Thank you @ABataev.
I've changes to the correct way to avoid extract with scalable, as you suggested, in the cost.

[ABataev]

LG

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

void BoUpSLP::buildTree_rec(ArrayRef<Value *> VL, unsigned Depth,
 
   InstructionsState S = getSameOpcode(VL);
   if (Depth == RecursionMaxDepth) {
     LLVM_DEBUG(dbgs() << "SLP: Gathering due to max recursion depth.\n");
     newTreeEntry(VL, None /*not vectorized*/, S, UserTreeIdx);
     return;
   }
 
+  // Don't handle scalable vectors
+  if (S.getOpcode() == Instruction::ExtractElement &&
+      isa<ScalableVectorType>(
+          cast<ExtractElementInst>(S.OpValue)->getVectorOperandType())) {
+    LLVM_DEBUG(dbgs() << "SLP: Gathering due to scalable vector type.\n");
+    newTreeEntry(VL, None /*not vectorized*/, S, UserTreeIdx);
+    return;
+  }
+
   // Don't handle vectors.
   if (S.OpValue->getType()->isVectorTy() &&
       !isa<InsertElementInst>(S.OpValue)) {
     LLVM_DEBUG(dbgs() << "SLP: Gathering due to vector type.\n");
     newTreeEntry(VL, None /*not vectorized*/, S, UserTreeIdx);
     return;
   }
 
if (E->State == TreeEntry::NeedToGather) {
     if (isSplat(VL)) {
       // Found the broadcasting of the single scalar, calculate the cost as the
       // broadcast.
       return ReuseShuffleCost +
              TTI->getShuffleCost(TargetTransformInfo::SK_Broadcast, VecTy, None,
                                  0);
     }
     if (E->getOpcode() == Instruction::ExtractElement && allSameType(VL) &&
-        allSameBlock(VL)) {
+        allSameBlock(VL) &&
+        !isa<ScalableVectorType>(
+            cast<ExtractElementInst>(E->getMainOp())->getVectorOperandType())) {
       // Check that gather of extractelements can be represented as just a
       // shuffle of a single/two vectors the scalars are extracted from.
       SmallVector<int> Mask;
       Optional<TargetTransformInfo::ShuffleKind> ShuffleKind =
           isShuffle(VL, Mask);
       if (ShuffleKind.hasValue()) {
         // Found the bunch of extractelement instructions that must be gathered
         // into a vector and can be represented as a permutation elements in a
         // single input vector or of 2 input vectors.
         InstructionCost Cost =
             computeExtractCost(VL, VecTy, *ShuffleKind, Mask, *TTI);
         AdjustExtractsCost(Cost, /*IsGather=*/true);
         return ReuseShuffleCost + Cost;
       }
     }
     return ReuseShuffleCost + getGatherCost(VL);

llvm/test/Transforms/SLPVectorizer/AArch64/scalable-vector.ll

 if.then:
   br label %end
 
 end:
   %retval = phi <vscale x 4 x i32> [ %a, %entry ], [ zeroinitializer, %if.then ]
   ret <vscale x 4 x i32> %retval
 }
 
+define void @scalable_phi1() {
+; CHECK-LABEL: @scalable_phi1(
+; CHECK-NEXT:  middle.block:
+; CHECK-NEXT:    [[EXTRACT1:%.*]] = extractelement <vscale x 8 x i16> undef, i32 undef
+; CHECK-NEXT:    [[EXTRACT2:%.*]] = extractelement <vscale x 8 x i16> undef, i32 undef
+; CHECK-NEXT:    br label [[FOR_BODY_I:%.*]]
+; CHECK:       for.body.i:
+; CHECK-NEXT:    [[RECUR1:%.*]] = phi i16 [ [[EXTRACT1]], [[MIDDLE_BLOCK:%.*]] ], [ undef, [[FOR_BODY_I]] ]
+; CHECK-NEXT:    [[RECUR2:%.*]] = phi i16 [ [[EXTRACT2]], [[MIDDLE_BLOCK]] ], [ undef, [[FOR_BODY_I]] ]
+; CHECK-NEXT:    br label [[FOR_BODY_I]]
+;
+middle.block:
+  %extract1 = extractelement <vscale x 8 x i16> undef, i32 undef
+  %extract2 = extractelement <vscale x 8 x i16> undef, i32 undef
+  br label %for.body.i
+
+for.body.i:                                       ; preds = %for.body.i, %middle.block
+  %recur1 = phi i16 [ %extract1, %middle.block ], [ undef, %for.body.i ]
+  %recur2 = phi i16 [ %extract2, %middle.block ], [ undef, %for.body.i ]
+  br label %for.body.i
+}
+
+define void @scalable_phi2() {
+; CHECK-LABEL: @scalable_phi2(
+; CHECK-NEXT:  middle.block:
+; CHECK-NEXT:    [[EXTRACT1:%.*]] = extractelement <vscale x 8 x i16> undef, i32 undef
+; CHECK-NEXT:    [[EXTRACT2:%.*]] = extractelement <vscale x 8 x i16> undef, i32 undef
+; CHECK-NEXT:    br label [[FOR_BODY_I:%.*]]
+; CHECK:       for.body.i:
+; CHECK-NEXT:    [[RECUR1:%.*]] = phi i16 [ undef, [[FOR_BODY_I]] ], [ [[EXTRACT1]], [[MIDDLE_BLOCK:%.*]] ]
+; CHECK-NEXT:    [[RECUR2:%.*]] = phi i16 [ undef, [[FOR_BODY_I]] ], [ [[EXTRACT2]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[FOR_BODY_I]]
+;
+middle.block:
+  %extract1 = extractelement <vscale x 8 x i16> undef, i32 undef
+  %extract2 = extractelement <vscale x 8 x i16> undef, i32 undef
+  br label %for.body.i
+
+for.body.i:                                       ; preds = %for.body.i, %middle.block
+  %recur1 = phi i16 [ undef, %for.body.i ], [ %extract1, %middle.block ]
+  %recur2 = phi i16 [ undef, %for.body.i ], [ %extract2, %middle.block ]
+  br label %for.body.i
+}
+
+define <vscale x 4 x i32> @build_vec_v4i32_reuse_0(<vscale x 2 x i32> %v0) {
+; CHECK-LABEL: @build_vec_v4i32_reuse_0(
+; CHECK-NEXT:    [[V0_0:%.*]] = extractelement <vscale x 2 x i32> [[V0:%.*]], i32 0
+; CHECK-NEXT:    [[V0_1:%.*]] = extractelement <vscale x 2 x i32> [[V0]], i32 1
+; CHECK-NEXT:    [[TMP0_0:%.*]] = add i32 [[V0_0]], [[V0_0]]
+; CHECK-NEXT:    [[TMP1_0:%.*]] = sub i32 [[V0_0]], [[V0_1]]
+; CHECK-NEXT:    [[TMP2_0:%.*]] = add i32 [[TMP0_0]], [[TMP1_0]]
+; CHECK-NEXT:    [[TMP3_0:%.*]] = insertelement <vscale x 4 x i32> undef, i32 [[TMP2_0]], i32 0
+; CHECK-NEXT:    ret <vscale x 4 x i32> [[TMP3_0]]
+;
+  %v0.0 = extractelement <vscale x 2 x i32> %v0, i32 0
+  %v0.1 = extractelement <vscale x 2 x i32> %v0, i32 1
+  %tmp0.0 = add i32 %v0.0, %v0.0
+  %tmp1.0 = sub i32 %v0.0, %v0.1
+  %tmp2.0 = add i32 %tmp0.0, %tmp1.0
+  %tmp3.0 = insertelement <vscale x 4 x i32> undef, i32 %tmp2.0, i32 0
+  ret <vscale x 4 x i32> %tmp3.0
+}
+
+define <vscale x 4 x i8> @shuffle(<4 x i8> %x, <4 x i8> %y) {
+; CHECK-LABEL: @shuffle(
+; CHECK-NEXT:    [[X0:%.*]] = extractelement <4 x i8> [[X:%.*]], i32 0
+; CHECK-NEXT:    [[X3:%.*]] = extractelement <4 x i8> [[X]], i32 3
+; CHECK-NEXT:    [[Y1:%.*]] = extractelement <4 x i8> [[Y:%.*]], i32 1
+; CHECK-NEXT:    [[Y2:%.*]] = extractelement <4 x i8> [[Y]], i32 2
+; CHECK-NEXT:    [[X0X0:%.*]] = mul i8 [[X0]], [[X0]]
+; CHECK-NEXT:    [[X3X3:%.*]] = mul i8 [[X3]], [[X3]]
+; CHECK-NEXT:    [[Y1Y1:%.*]] = mul i8 [[Y1]], [[Y1]]
+; CHECK-NEXT:    [[Y2Y2:%.*]] = mul i8 [[Y2]], [[Y2]]
+; CHECK-NEXT:    [[INS1:%.*]] = insertelement <vscale x 4 x i8> poison, i8 [[X0X0]], i32 0
+; CHECK-NEXT:    [[INS2:%.*]] = insertelement <vscale x 4 x i8> [[INS1]], i8 [[X3X3]], i32 1
+; CHECK-NEXT:    [[INS3:%.*]] = insertelement <vscale x 4 x i8> [[INS2]], i8 [[Y1Y1]], i32 2
+; CHECK-NEXT:    [[INS4:%.*]] = insertelement <vscale x 4 x i8> [[INS3]], i8 [[Y2Y2]], i32 3
+; CHECK-NEXT:    ret <vscale x 4 x i8> [[INS4]]
+;
+  %x0 = extractelement <4 x i8> %x, i32 0
+  %x3 = extractelement <4 x i8> %x, i32 3
+  %y1 = extractelement <4 x i8> %y, i32 1
+  %y2 = extractelement <4 x i8> %y, i32 2
+  %x0x0 = mul i8 %x0, %x0
+  %x3x3 = mul i8 %x3, %x3
+  %y1y1 = mul i8 %y1, %y1
+  %y2y2 = mul i8 %y2, %y2
+  %ins1 = insertelement <vscale x 4 x i8> poison, i8 %x0x0, i32 0
+  %ins2 = insertelement <vscale x 4 x i8> %ins1, i8 %x3x3, i32 1
+  %ins3 = insertelement <vscale x 4 x i8> %ins2, i8 %y1y1, i32 2
+  %ins4 = insertelement <vscale x 4 x i8> %ins3, i8 %y2y2, i32 3
+  ret  <vscale x 4 x i8> %ins4
+}
+
 declare <vscale x 16 x i8> @llvm.masked.load.nxv16i8.p0nxv16i8(<vscale x 16 x i8>*, i32 immarg, <vscale x 16 x i1>, <vscale x 16 x i8>)
 declare void @llvm.masked.store.nxv16i8.p0nxv16i8(<vscale x 16 x i8>, <vscale x 16 x i8>*, i32 immarg, <vscale x 16 x i1>)