[VPlan] Support scalable vectors in outer-loop vectorization

[iamlouk]

Summary

This patch enables scalable vectors in the VPlan-native path.
If a vectorization factor is specified via loop vectorization hints,
that factor is used. If no vectorization factor is specified, but the
target preferes scalable vectorization, a scalable vectorization factor
is selected.

[iamlouk]

Rebase and add call to reportVectorizationFailure()

[iamlouk]

Rebase

[iamlouk]

Fix clang-format

[fhahn]

Looks reasonable overall, my only concern is that this adds another codepath to the native path which is already lacking test coverage in general. Do you have any idea/suggestion on how to improve end-to-end test coverage, e.g. in llvm-test-suite (could be adding some SingleSource tests with loop nests and #pragma clang loop vectorize_width(4)?

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

7384

Can a test be added for this case?

[iamlouk]

Add check for optimization remarks and rejection of scalable VFs on targets without scalable vectors.

[iamlouk]

In D157484#4628634, @fhahn wrote:

Looks reasonable overall, my only concern is that this adds another codepath to the native path which is already lacking test coverage in general. Do you have any idea/suggestion on how to improve end-to-end test coverage, e.g. in llvm-test-suite (could be adding some SingleSource tests with loop nests and #pragma clang loop vectorize_width(4)?

Thank you very much for your reply @fhahn! I have a private fork of the llvm-test-suite where I have something similar to this: A subdirectory VPlanNativePath in llvm-test-suite/SingleSource/UnitTests/Vectorizer/ that is only added to the CMake build if the compiler is clang. In that directory, I also add -mllvm -enable-vplan-native-path to the CMAKE_C_FLAGS and it contains simple tests that initialise some 1d and 2d arrays, does some operations on them (with loops that have #pragma clang loop vectorize(enable) in front of them), and prints the result arrays to stdout (for checking against a reference). If this general approach would be fine with you, I will happily submit patches with the tests that already outer-loop-vectorize with the current upstream functionality!

Might I assume your judgement on D157371 (#pragma [...] interleave_count(2) for the VPlan-native path) is similar to the comment here?

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

7384

Thank you for the feedback, I added a second RUN: line to llvm/test/Transforms/LoopVectorize/outer_loop_scalable.ll where scalable vectors are not enabled and added CHECK lines for the optimization remarks.

[fhahn]

In D157484#4630552, @iamlouk wrote:

In D157484#4628634, @fhahn wrote:

Looks reasonable overall, my only concern is that this adds another codepath to the native path which is already lacking test coverage in general. Do you have any idea/suggestion on how to improve end-to-end test coverage, e.g. in llvm-test-suite (could be adding some SingleSource tests with loop nests and #pragma clang loop vectorize_width(4)?

Thank you very much for your reply @fhahn! I have a private fork of the llvm-test-suite where I have something similar to this: A subdirectory VPlanNativePath in llvm-test-suite/SingleSource/UnitTests/Vectorizer/ that is only added to the CMake build if the compiler is clang. In that directory, I also add -mllvm -enable-vplan-native-path to the CMAKE_C_FLAGS and it contains simple tests that initialise some 1d and 2d arrays, does some operations on them (with loops that have #pragma clang loop vectorize(enable) in front of them), and prints the result arrays to stdout (for checking against a reference). If this general approach would be fine with you, I will happily submit patches with the tests that already outer-loop-vectorize with the current upstream functionality!

Might I assume your judgement on D157371 (#pragma [...] interleave_count(2) for the VPlan-native path) is similar to the comment here?

That sounds like a good first step, can you share a patch for that?

[iamlouk]

In D157484#4638295, @fhahn wrote:

That sounds like a good first step, can you share a patch for that?

Sorry for the delay, here it is: https://github.com/llvm/llvm-test-suite/pull/20 ! I did not find a way to request reviewers (the usual link was greyed out for me) in the GitHub PR, so sorry for using a comment to tag you there.

[fhahn]

LGTM, thanks!

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

7345–7346

might be good to document here that this will pick a scalable VF if target supports scalable vectors or fixed one otherwise (before TODO)

[iamlouk]

Rebase and add comment on VF selection.

[fhahn]

I didn't realize this hasn't landed yet. @iamlouk would you like me to commit this on your behalf? If so, please let me know the name + email to use to set as author of the commit.

[iamlouk]

Yes, thank you: Lou Knauer <[e-mail]>

[fhahn]

In D157484#4654586, @iamlouk wrote:

Yes, thank you: Lou Knauer <[e-mail]>

Great, will do! Unfortunately it looks like this doesn't apply cleaning. Could you rebase it?

[fhahn]

In D157484#4654586, @iamlouk wrote:

Yes, thank you: Lou Knauer <[e-mail]>

Great, will do! Unfortunately it looks like this doesn't apply cleaning. Could you rebase it?

[iamlouk]

Rebase

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

void LoopVectorizationCostModel::collectInLoopReductions() {
   }
 }
 
 // TODO: we could return a pair of values that specify the max VF and
 // min VF, to be used in `buildVPlans(MinVF, MaxVF)` instead of
 // `buildVPlans(VF, VF)`. We cannot do it because VPLAN at the moment
 // doesn't have a cost model that can choose which plan to execute if
 // more than one is generated.
-static unsigned determineVPlanVF(const unsigned WidestVectorRegBits,
+static ElementCount determineVPlanVF(const TargetTransformInfo &TTI,
                                      LoopVectorizationCostModel &CM) {
   unsigned WidestType;
   std::tie(std::ignore, WidestType) = CM.getSmallestAndWidestTypes();
-  return WidestVectorRegBits / WidestType;
+
+  TargetTransformInfo::RegisterKind RegKind =
+      TTI.enableScalableVectorization()
+          ? TargetTransformInfo::RGK_ScalableVector
+          : TargetTransformInfo::RGK_FixedWidthVector;
+
+  TypeSize RegSize = TTI.getRegisterBitWidth(RegKind);
+  unsigned N = RegSize.getKnownMinValue() / WidestType;
+  return ElementCount::get(N, RegSize.isScalable());
 }
 
 VectorizationFactor
 LoopVectorizationPlanner::planInVPlanNativePath(ElementCount UserVF) {
-  assert(!UserVF.isScalable() && "scalable vectors not yet supported");
   ElementCount VF = UserVF;
   // Outer loop handling: They may require CFG and instruction level
   // transformations before even evaluating whether vectorization is profitable.
   // Since we cannot modify the incoming IR, we need to build VPlan upfront in
   // the vectorization pipeline.
   if (!OrigLoop->isInnermost()) {
     // If the user doesn't provide a vectorization factor, determine a
     // reasonable one.
     if (UserVF.isZero()) {
-      VF = ElementCount::getFixed(determineVPlanVF(
-          TTI.getRegisterBitWidth(TargetTransformInfo::RGK_FixedWidthVector)
-              .getFixedValue(),
-          CM));
+      VF = determineVPlanVF(TTI, CM);
       LLVM_DEBUG(dbgs() << "LV: VPlan computed VF " << VF << ".\n");
 
       // Make sure we have a VF > 1 for stress testing.
       if (VPlanBuildStressTest && (VF.isScalar() || VF.isZero())) {
         LLVM_DEBUG(dbgs() << "LV: VPlan stress testing: "
                           << "overriding computed VF.\n");
         VF = ElementCount::getFixed(4);
       }
+    } else if (UserVF.isScalable() && !TTI.supportsScalableVectors() &&
+               !ForceTargetSupportsScalableVectors) {
+      LLVM_DEBUG(dbgs() << "LV: Not vectorizing. Scalable VF requested, but "
+                        << "not supported by the target.\n");
+      reportVectorizationFailure(
+          "Scalable vectorization requested but not supported by the target",
+          "the scalable user-specified vectorization width for outer-loop "
+          "vectorization cannot be used because the target does not support "
+          "scalable vectors.", "ScalableVFUnfeasible", ORE, OrigLoop);
+      return VectorizationFactor::Disabled();
     }
     assert(EnableVPlanNativePath && "VPlan-native path is not enabled.");
     assert(isPowerOf2_32(VF.getKnownMinValue()) &&
            "VF needs to be a power of two");
     LLVM_DEBUG(dbgs() << "LV: Using " << (!UserVF.isZero() ? "user " : "")
                       << "VF " << VF << " to build VPlans.\n");
     buildVPlans(VF, VF);
 

llvm/test/Transforms/LoopVectorize/AArch64/outer_loop_prefer_scalable.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt -S -mtriple aarch64 -mattr=+sve -passes=loop-vectorize -enable-vplan-native-path < %s | FileCheck %s
+
+@A = external local_unnamed_addr global [1024 x float], align 4
+@B = external local_unnamed_addr global [512 x float], align 4
+
+; Test if the vplan-native-path successfully vectorizes a loop using scalable vectors if the target preferes scalable vectors.
+define void @foo() {
+; CHECK-LABEL: define void @foo
+; CHECK-SAME: () #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP1:%.*]] = mul i64 [[TMP0]], 4
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 1024, [[TMP1]]
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    [[TMP2:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP3:%.*]] = mul i64 [[TMP2]], 4
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 1024, [[TMP3]]
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 1024, [[N_MOD_VF]]
+; CHECK-NEXT:    [[TMP4:%.*]] = call <vscale x 4 x i64> @llvm.experimental.stepvector.nxv4i64()
+; CHECK-NEXT:    [[TMP5:%.*]] = add <vscale x 4 x i64> [[TMP4]], zeroinitializer
+; CHECK-NEXT:    [[TMP6:%.*]] = mul <vscale x 4 x i64> [[TMP5]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 1, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[INDUCTION:%.*]] = add <vscale x 4 x i64> zeroinitializer, [[TMP6]]
+; CHECK-NEXT:    [[TMP7:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP8:%.*]] = mul i64 [[TMP7]], 4
+; CHECK-NEXT:    [[TMP9:%.*]] = mul i64 1, [[TMP8]]
+; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <vscale x 4 x i64> poison, i64 [[TMP9]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <vscale x 4 x i64> [[DOTSPLATINSERT]], <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[OUTER_LOOP_LATCH4:%.*]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <vscale x 4 x i64> [ [[INDUCTION]], [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[OUTER_LOOP_LATCH4]] ]
+; CHECK-NEXT:    [[TMP10:%.*]] = getelementptr inbounds [1024 x float], ptr @A, i64 0, <vscale x 4 x i64> [[VEC_IND]]
+; CHECK-NEXT:    [[WIDE_MASKED_GATHER:%.*]] = call <vscale x 4 x float> @llvm.masked.gather.nxv4f32.nxv4p0(<vscale x 4 x ptr> [[TMP10]], i32 4, <vscale x 4 x i1> shufflevector (<vscale x 4 x i1> insertelement (<vscale x 4 x i1> poison, i1 true, i64 0), <vscale x 4 x i1> poison, <vscale x 4 x i32> zeroinitializer), <vscale x 4 x float> poison)
+; CHECK-NEXT:    br label [[INNER_LOOP1:%.*]]
+; CHECK:       inner_loop1:
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 4 x i64> [ zeroinitializer, [[VECTOR_BODY]] ], [ [[TMP13:%.*]], [[INNER_LOOP1]] ]
+; CHECK-NEXT:    [[VEC_PHI2:%.*]] = phi <vscale x 4 x float> [ [[WIDE_MASKED_GATHER]], [[VECTOR_BODY]] ], [ [[TMP12:%.*]], [[INNER_LOOP1]] ]
+; CHECK-NEXT:    [[TMP11:%.*]] = getelementptr inbounds [512 x float], ptr @B, i64 0, <vscale x 4 x i64> [[VEC_PHI]]
+; CHECK-NEXT:    [[WIDE_MASKED_GATHER3:%.*]] = call <vscale x 4 x float> @llvm.masked.gather.nxv4f32.nxv4p0(<vscale x 4 x ptr> [[TMP11]], i32 4, <vscale x 4 x i1> shufflevector (<vscale x 4 x i1> insertelement (<vscale x 4 x i1> poison, i1 true, i64 0), <vscale x 4 x i1> poison, <vscale x 4 x i32> zeroinitializer), <vscale x 4 x float> poison)
+; CHECK-NEXT:    [[TMP12]] = fmul <vscale x 4 x float> [[VEC_PHI2]], [[WIDE_MASKED_GATHER3]]
+; CHECK-NEXT:    [[TMP13]] = add nuw nsw <vscale x 4 x i64> [[VEC_PHI]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 1, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[TMP14:%.*]] = icmp eq <vscale x 4 x i64> [[TMP13]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 512, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[TMP15:%.*]] = extractelement <vscale x 4 x i1> [[TMP14]], i32 0
+; CHECK-NEXT:    br i1 [[TMP15]], label [[OUTER_LOOP_LATCH4]], label [[INNER_LOOP1]]
+; CHECK:       outer_loop_latch4:
+; CHECK-NEXT:    [[VEC_PHI5:%.*]] = phi <vscale x 4 x float> [ [[TMP12]], [[INNER_LOOP1]] ]
+; CHECK-NEXT:    call void @llvm.masked.scatter.nxv4f32.nxv4p0(<vscale x 4 x float> [[VEC_PHI5]], <vscale x 4 x ptr> [[TMP10]], i32 4, <vscale x 4 x i1> shufflevector (<vscale x 4 x i1> insertelement (<vscale x 4 x i1> poison, i1 true, i64 0), <vscale x 4 x i1> poison, <vscale x 4 x i32> zeroinitializer))
+; CHECK-NEXT:    [[TMP16:%.*]] = add nuw nsw <vscale x 4 x i64> [[VEC_IND]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 1, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[TMP17:%.*]] = icmp eq <vscale x 4 x i64> [[TMP16]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 1024, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[TMP18:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP19:%.*]] = mul i64 [[TMP18]], 4
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP19]]
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <vscale x 4 x i64> [[VEC_IND]], [[DOTSPLAT]]
+; CHECK-NEXT:    [[TMP20:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP20]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 1024, [[N_VEC]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    br label [[OUTER_LOOP:%.*]]
+; CHECK:       outer_loop:
+; CHECK-NEXT:    [[I:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[I_NEXT:%.*]], [[OUTER_LOOP_LATCH:%.*]] ]
+; CHECK-NEXT:    [[ARRAYIDX1:%.*]] = getelementptr inbounds [1024 x float], ptr @A, i64 0, i64 [[I]]
+; CHECK-NEXT:    [[X_START:%.*]] = load float, ptr [[ARRAYIDX1]], align 4
+; CHECK-NEXT:    br label [[INNER_LOOP:%.*]]
+; CHECK:       inner_loop:
+; CHECK-NEXT:    [[J:%.*]] = phi i64 [ 0, [[OUTER_LOOP]] ], [ [[J_NEXT:%.*]], [[INNER_LOOP]] ]
+; CHECK-NEXT:    [[X:%.*]] = phi float [ [[X_START]], [[OUTER_LOOP]] ], [ [[X_NEXT:%.*]], [[INNER_LOOP]] ]
+; CHECK-NEXT:    [[ARRAYIDX2:%.*]] = getelementptr inbounds [512 x float], ptr @B, i64 0, i64 [[J]]
+; CHECK-NEXT:    [[B:%.*]] = load float, ptr [[ARRAYIDX2]], align 4
+; CHECK-NEXT:    [[X_NEXT]] = fmul float [[X]], [[B]]
+; CHECK-NEXT:    [[J_NEXT]] = add nuw nsw i64 [[J]], 1
+; CHECK-NEXT:    [[INNER_EXITCOND:%.*]] = icmp eq i64 [[J_NEXT]], 512
+; CHECK-NEXT:    br i1 [[INNER_EXITCOND]], label [[OUTER_LOOP_LATCH]], label [[INNER_LOOP]]
+; CHECK:       outer_loop_latch:
+; CHECK-NEXT:    [[X_NEXT_LCSSA:%.*]] = phi float [ [[X_NEXT]], [[INNER_LOOP]] ]
+; CHECK-NEXT:    store float [[X_NEXT_LCSSA]], ptr [[ARRAYIDX1]], align 4
+; CHECK-NEXT:    [[I_NEXT]] = add nuw nsw i64 [[I]], 1
+; CHECK-NEXT:    [[OUTER_EXITCOND:%.*]] = icmp eq i64 [[I_NEXT]], 1024
+; CHECK-NEXT:    br i1 [[OUTER_EXITCOND]], label [[EXIT]], label [[OUTER_LOOP]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %outer_loop
+
+outer_loop:
+  %i = phi i64 [ 0, %entry ], [ %i.next, %outer_loop_latch ]
+  %arrayidx1 = getelementptr inbounds [1024 x float], ptr @A, i64 0, i64 %i
+  %x.start = load float, ptr %arrayidx1, align 4
+  br label %inner_loop
+
+inner_loop:
+  %j = phi i64 [ 0, %outer_loop ], [ %j.next, %inner_loop ]
+  %x = phi float [ %x.start, %outer_loop ], [ %x.next, %inner_loop ]
+  %arrayidx2 = getelementptr inbounds [512 x float], ptr @B, i64 0, i64 %j
+  %b = load float, ptr %arrayidx2, align 4
+  %x.next = fmul float %x, %b
+  %j.next = add nuw nsw i64 %j, 1
+  %inner_exitcond = icmp eq i64 %j.next, 512
+  br i1 %inner_exitcond, label %outer_loop_latch, label %inner_loop
+
+outer_loop_latch:
+  store float %x.next, ptr %arrayidx1, align 4
+  %i.next = add nuw nsw i64 %i, 1
+  %outer_exitcond = icmp eq i64 %i.next, 1024
+  br i1 %outer_exitcond, label %exit, label %outer_loop, !llvm.loop !1
+
+exit:
+  ret void
+}
+
+!1 = distinct !{!1, !2}
+!2 = !{!"llvm.loop.vectorize.enable", i1 true}

llvm/test/Transforms/LoopVectorize/outer_loop_scalable.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt -S -force-target-supports-scalable-vectors -passes=loop-vectorize -enable-vplan-native-path < %s | FileCheck %s
+
+@A = external local_unnamed_addr global [1024 x float], align 4
+@B = external local_unnamed_addr global [512 x float], align 4
+
+; Test if the vplan-native-path successfully vectorizes a loop using scalable vectors if the user-specified VF is scalable.
+define void @foo() {
+; CHECK-LABEL: define void @foo() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP1:%.*]] = mul i64 [[TMP0]], 4
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 1024, [[TMP1]]
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    [[TMP2:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP3:%.*]] = mul i64 [[TMP2]], 4
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 1024, [[TMP3]]
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 1024, [[N_MOD_VF]]
+; CHECK-NEXT:    [[TMP4:%.*]] = call <vscale x 4 x i64> @llvm.experimental.stepvector.nxv4i64()
+; CHECK-NEXT:    [[TMP5:%.*]] = add <vscale x 4 x i64> [[TMP4]], zeroinitializer
+; CHECK-NEXT:    [[TMP6:%.*]] = mul <vscale x 4 x i64> [[TMP5]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 1, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[INDUCTION:%.*]] = add <vscale x 4 x i64> zeroinitializer, [[TMP6]]
+; CHECK-NEXT:    [[TMP7:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP8:%.*]] = mul i64 [[TMP7]], 4
+; CHECK-NEXT:    [[TMP9:%.*]] = mul i64 1, [[TMP8]]
+; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <vscale x 4 x i64> poison, i64 [[TMP9]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <vscale x 4 x i64> [[DOTSPLATINSERT]], <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[OUTER_LOOP_LATCH4:%.*]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <vscale x 4 x i64> [ [[INDUCTION]], [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[OUTER_LOOP_LATCH4]] ]
+; CHECK-NEXT:    [[TMP10:%.*]] = getelementptr inbounds [1024 x float], ptr @A, i64 0, <vscale x 4 x i64> [[VEC_IND]]
+; CHECK-NEXT:    [[WIDE_MASKED_GATHER:%.*]] = call <vscale x 4 x float> @llvm.masked.gather.nxv4f32.nxv4p0(<vscale x 4 x ptr> [[TMP10]], i32 4, <vscale x 4 x i1> shufflevector (<vscale x 4 x i1> insertelement (<vscale x 4 x i1> poison, i1 true, i64 0), <vscale x 4 x i1> poison, <vscale x 4 x i32> zeroinitializer), <vscale x 4 x float> poison)
+; CHECK-NEXT:    br label [[INNER_LOOP1:%.*]]
+; CHECK:       inner_loop1:
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 4 x i64> [ zeroinitializer, [[VECTOR_BODY]] ], [ [[TMP13:%.*]], [[INNER_LOOP1]] ]
+; CHECK-NEXT:    [[VEC_PHI2:%.*]] = phi <vscale x 4 x float> [ [[WIDE_MASKED_GATHER]], [[VECTOR_BODY]] ], [ [[TMP12:%.*]], [[INNER_LOOP1]] ]
+; CHECK-NEXT:    [[TMP11:%.*]] = getelementptr inbounds [512 x float], ptr @B, i64 0, <vscale x 4 x i64> [[VEC_PHI]]
+; CHECK-NEXT:    [[WIDE_MASKED_GATHER3:%.*]] = call <vscale x 4 x float> @llvm.masked.gather.nxv4f32.nxv4p0(<vscale x 4 x ptr> [[TMP11]], i32 4, <vscale x 4 x i1> shufflevector (<vscale x 4 x i1> insertelement (<vscale x 4 x i1> poison, i1 true, i64 0), <vscale x 4 x i1> poison, <vscale x 4 x i32> zeroinitializer), <vscale x 4 x float> poison)
+; CHECK-NEXT:    [[TMP12]] = fmul <vscale x 4 x float> [[VEC_PHI2]], [[WIDE_MASKED_GATHER3]]
+; CHECK-NEXT:    [[TMP13]] = add nuw nsw <vscale x 4 x i64> [[VEC_PHI]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 1, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[TMP14:%.*]] = icmp eq <vscale x 4 x i64> [[TMP13]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 512, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[TMP15:%.*]] = extractelement <vscale x 4 x i1> [[TMP14]], i32 0
+; CHECK-NEXT:    br i1 [[TMP15]], label [[OUTER_LOOP_LATCH4]], label [[INNER_LOOP1]]
+; CHECK:       outer_loop_latch4:
+; CHECK-NEXT:    [[VEC_PHI5:%.*]] = phi <vscale x 4 x float> [ [[TMP12]], [[INNER_LOOP1]] ]
+; CHECK-NEXT:    call void @llvm.masked.scatter.nxv4f32.nxv4p0(<vscale x 4 x float> [[VEC_PHI5]], <vscale x 4 x ptr> [[TMP10]], i32 4, <vscale x 4 x i1> shufflevector (<vscale x 4 x i1> insertelement (<vscale x 4 x i1> poison, i1 true, i64 0), <vscale x 4 x i1> poison, <vscale x 4 x i32> zeroinitializer))
+; CHECK-NEXT:    [[TMP16:%.*]] = add nuw nsw <vscale x 4 x i64> [[VEC_IND]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 1, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[TMP17:%.*]] = icmp eq <vscale x 4 x i64> [[TMP16]], shufflevector (<vscale x 4 x i64> insertelement (<vscale x 4 x i64> poison, i64 1024, i64 0), <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer)
+; CHECK-NEXT:    [[TMP18:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP19:%.*]] = mul i64 [[TMP18]], 4
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP19]]
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <vscale x 4 x i64> [[VEC_IND]], [[DOTSPLAT]]
+; CHECK-NEXT:    [[TMP20:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP20]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 1024, [[N_VEC]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    br label [[OUTER_LOOP:%.*]]
+; CHECK:       outer_loop:
+; CHECK-NEXT:    [[I:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[I_NEXT:%.*]], [[OUTER_LOOP_LATCH:%.*]] ]
+; CHECK-NEXT:    [[ARRAYIDX1:%.*]] = getelementptr inbounds [1024 x float], ptr @A, i64 0, i64 [[I]]
+; CHECK-NEXT:    [[X_START:%.*]] = load float, ptr [[ARRAYIDX1]], align 4
+; CHECK-NEXT:    br label [[INNER_LOOP:%.*]]
+; CHECK:       inner_loop:
+; CHECK-NEXT:    [[J:%.*]] = phi i64 [ 0, [[OUTER_LOOP]] ], [ [[J_NEXT:%.*]], [[INNER_LOOP]] ]
+; CHECK-NEXT:    [[X:%.*]] = phi float [ [[X_START]], [[OUTER_LOOP]] ], [ [[X_NEXT:%.*]], [[INNER_LOOP]] ]
+; CHECK-NEXT:    [[ARRAYIDX2:%.*]] = getelementptr inbounds [512 x float], ptr @B, i64 0, i64 [[J]]
+; CHECK-NEXT:    [[B:%.*]] = load float, ptr [[ARRAYIDX2]], align 4
+; CHECK-NEXT:    [[X_NEXT]] = fmul float [[X]], [[B]]
+; CHECK-NEXT:    [[J_NEXT]] = add nuw nsw i64 [[J]], 1
+; CHECK-NEXT:    [[INNER_EXITCOND:%.*]] = icmp eq i64 [[J_NEXT]], 512
+; CHECK-NEXT:    br i1 [[INNER_EXITCOND]], label [[OUTER_LOOP_LATCH]], label [[INNER_LOOP]]
+; CHECK:       outer_loop_latch:
+; CHECK-NEXT:    [[X_NEXT_LCSSA:%.*]] = phi float [ [[X_NEXT]], [[INNER_LOOP]] ]
+; CHECK-NEXT:    store float [[X_NEXT_LCSSA]], ptr [[ARRAYIDX1]], align 4
+; CHECK-NEXT:    [[I_NEXT]] = add nuw nsw i64 [[I]], 1
+; CHECK-NEXT:    [[OUTER_EXITCOND:%.*]] = icmp eq i64 [[I_NEXT]], 1024
+; CHECK-NEXT:    br i1 [[OUTER_EXITCOND]], label [[EXIT]], label [[OUTER_LOOP]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %outer_loop
+
+outer_loop:
+  %i = phi i64 [ 0, %entry ], [ %i.next, %outer_loop_latch ]
+  %arrayidx1 = getelementptr inbounds [1024 x float], ptr @A, i64 0, i64 %i
+  %x.start = load float, ptr %arrayidx1, align 4
+  br label %inner_loop
+
+inner_loop:
+  %j = phi i64 [ 0, %outer_loop ], [ %j.next, %inner_loop ]
+  %x = phi float [ %x.start, %outer_loop ], [ %x.next, %inner_loop ]
+  %arrayidx2 = getelementptr inbounds [512 x float], ptr @B, i64 0, i64 %j
+  %b = load float, ptr %arrayidx2, align 4
+  %x.next = fmul float %x, %b
+  %j.next = add nuw nsw i64 %j, 1
+  %inner_exitcond = icmp eq i64 %j.next, 512
+  br i1 %inner_exitcond, label %outer_loop_latch, label %inner_loop
+
+outer_loop_latch:
+  store float %x.next, ptr %arrayidx1, align 4
+  %i.next = add nuw nsw i64 %i, 1
+  %outer_exitcond = icmp eq i64 %i.next, 1024
+  br i1 %outer_exitcond, label %exit, label %outer_loop, !llvm.loop !1
+
+exit:
+  ret void
+}
+
+!1 = distinct !{!1, !2, !3, !4}
+!2 = !{!"llvm.loop.vectorize.enable", i1 true}
+!3 = !{!"llvm.loop.vectorize.scalable.enable", i1 true}
+!4 = !{!"llvm.loop.vectorize.width", i32 4}