[VPlan] Move addExplicitVectorLength to tryToBuildVPlanWithVPRecipes

Stacked on #166158

Currently we convert a VPlan to an EVL tail folded one after the VPlan is built and optimized, which doesn't match how we handle regular tail folding.

This addresses a long standing TODO by performing it much earlier in the pipeline before any optimizations are run, and simulatneously splits out optimizeMaskToEVL into a separate pass to be run during VPlanTransforms::optimize.

This way the two parts of EVL tail folding are separated into those needed for correctness and those that are an optimization.

- We don't need to remove the old recipes ourselves anymore and can leave it to removeDeadRecipes
- createScalarIVSteps needs to be updated to use the EVL based IV if it exists, so a helper method was added to VPlan to extract it
- VPlanVerifier was updated to check that the EVL based IV always immediately follows the canonical IV

Because we now optimize the VPlan after the EVL stuff is added, some simplifications e.g. replacing a scalar-steps when UF=1 kick in for the initial VPlan.

Fixes #153144

Author: lukel97

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8232,10 +8232,6 @@ void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
       VPlanTransforms::runPass(VPlanTransforms::truncateToMinimalBitwidths,
                                *Plan, CM.getMinimalBitwidths());
       VPlanTransforms::runPass(VPlanTransforms::optimize, *Plan);
-      // TODO: try to put it close to addActiveLaneMask().
-      if (CM.foldTailWithEVL())
-        VPlanTransforms::runPass(VPlanTransforms::addExplicitVectorLength,
-                                 *Plan, CM.getMaxSafeElements());
       assert(verifyVPlanIsValid(*Plan) && "VPlan is invalid");
       VPlans.push_back(std::move(Plan));
     }
@@ -8499,6 +8495,9 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(
   }
   VPlanTransforms::optimizeInductionExitUsers(*Plan, IVEndValues, *PSE.getSE());
 
+  if (CM.foldTailWithEVL())
+    VPlanTransforms::addExplicitVectorLength(*Plan, CM.getMaxSafeElements());
+
   assert(verifyVPlanIsValid(*Plan) && "VPlan is invalid");
   return Plan;
 }

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -4114,6 +4114,11 @@ class LLVM_ABI_FOR_TEST VPRegionBlock : public VPBlockBase {
     return const_cast<VPRegionBlock *>(this)->getCanonicalIV();
   }
 
+  VPEVLBasedIVPHIRecipe *getEVLBasedIV() {
+    return dyn_cast<VPEVLBasedIVPHIRecipe>(
+        std::next(getCanonicalIV()->getIterator()));
+  }
+
   /// Return the type of the canonical IV for loop regions.
   Type *getCanonicalIVType() { return getCanonicalIV()->getScalarType(); }
   const Type *getCanonicalIVType() const {

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -605,9 +605,11 @@ createScalarIVSteps(VPlan &Plan, InductionDescriptor::InductionKind Kind,
                     VPBuilder &Builder) {
   VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
   VPBasicBlock *HeaderVPBB = LoopRegion->getEntryBasicBlock();
-  VPCanonicalIVPHIRecipe *CanonicalIV = LoopRegion->getCanonicalIV();
-  VPSingleDefRecipe *BaseIV = Builder.createDerivedIV(
-      Kind, FPBinOp, StartV, CanonicalIV, Step, "offset.idx");
+  VPValue *IV = LoopRegion->getCanonicalIV();
+  if (auto *EVLIV = LoopRegion->getEVLBasedIV())
+    IV = EVLIV;
+  VPSingleDefRecipe *BaseIV =
+      Builder.createDerivedIV(Kind, FPBinOp, StartV, IV, Step, "offset.idx");
 
   // Truncate base induction if needed.
   VPTypeAnalysis TypeInfo(Plan);
@@ -2331,6 +2333,7 @@ void VPlanTransforms::optimize(VPlan &Plan) {
   runPass(removeRedundantExpandSCEVRecipes, Plan);
   runPass(simplifyRecipes, Plan);
   runPass(removeBranchOnConst, Plan);
+  runPass(optimizeMasksToEVL, Plan);
   runPass(removeDeadRecipes, Plan);
 
   runPass(createAndOptimizeReplicateRegions, Plan);
@@ -2621,8 +2624,40 @@ static VPRecipeBase *optimizeMaskToEVL(VPValue *HeaderMask,
   return nullptr;
 }
 
-/// Replace recipes with their EVL variants.
-static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
+void VPlanTransforms::optimizeMasksToEVL(VPlan &Plan) {
+  // Find the EVL-based header mask if it exists: icmp ult step-vector, EVL
+  VPInstruction *HeaderMask = nullptr;
+  for (VPRecipeBase &R : *Plan.getVectorLoopRegion()->getEntryBasicBlock()) {
+    if (match(&R, m_ICmp(m_VPInstruction<VPInstruction::StepVector>(),
+                         m_EVL(m_VPValue())))) {
+      HeaderMask = cast<VPInstruction>(&R);
+      break;
+    }
+  }
+  if (!HeaderMask)
+    return;
+
+  VPValue *EVL = HeaderMask->getOperand(1);
+
+  VPTypeAnalysis TypeInfo(Plan);
+
+  for (VPUser *U : collectUsersRecursively(HeaderMask)) {
+    VPRecipeBase *R = cast<VPRecipeBase>(U);
+    if (auto *NewR = optimizeMaskToEVL(HeaderMask, *R, TypeInfo, *EVL)) {
+      NewR->insertBefore(R);
+      for (auto [Old, New] :
+           zip_equal(R->definedValues(), NewR->definedValues()))
+        Old->replaceAllUsesWith(New);
+      // Erase dead stores, the rest will be removed by removeDeadRecipes.
+      if (R->getNumDefinedValues() == 0)
+        R->eraseFromParent();
+    }
+  }
+}
+
+/// After replacing the IV with a EVL-based IV, fixup recipes that use VF to use
+/// the EVL instead to avoid incorrect updates on the penultimate iteration.
+static void fixupVFUsersForEVL(VPlan &Plan, VPValue &EVL) {
   VPTypeAnalysis TypeInfo(Plan);
   VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
   VPBasicBlock *Header = LoopRegion->getEntryBasicBlock();
@@ -2650,10 +2685,6 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
     return isa<VPWidenPointerInductionRecipe>(U);
   });
 
-  // Defer erasing recipes till the end so that we don't invalidate the
-  // VPTypeAnalysis cache.
-  SmallVector<VPRecipeBase *> ToErase;
-
   // Create a scalar phi to track the previous EVL if fixed-order recurrence is
   // contained.
   bool ContainsFORs =
@@ -2687,7 +2718,6 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
             TypeInfo.inferScalarType(R.getVPSingleValue()), R.getDebugLoc());
         VPSplice->insertBefore(&R);
         R.getVPSingleValue()->replaceAllUsesWith(VPSplice);
-        ToErase.push_back(&R);
       }
     }
   }
@@ -2708,43 +2738,6 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
       CmpInst::ICMP_ULT,
       Builder.createNaryOp(VPInstruction::StepVector, {}, EVLType), &EVL);
   HeaderMask->replaceAllUsesWith(EVLMask);
-  ToErase.push_back(HeaderMask->getDefiningRecipe());
-
-  // Try to optimize header mask recipes away to their EVL variants.
-  // TODO: Split optimizeMaskToEVL out and move into
-  // VPlanTransforms::optimize. transformRecipestoEVLRecipes should be run in
-  // tryToBuildVPlanWithVPRecipes beforehand.
-  for (VPUser *U : collectUsersRecursively(EVLMask)) {
-    auto *CurRecipe = cast<VPRecipeBase>(U);
-    VPRecipeBase *EVLRecipe =
-        optimizeMaskToEVL(EVLMask, *CurRecipe, TypeInfo, EVL);
-    if (!EVLRecipe)
-      continue;
-
-    unsigned NumDefVal = EVLRecipe->getNumDefinedValues();
-    assert(NumDefVal == CurRecipe->getNumDefinedValues() &&
-           "New recipe must define the same number of values as the "
-           "original.");
-    EVLRecipe->insertBefore(CurRecipe);
-    if (isa<VPSingleDefRecipe, VPWidenLoadEVLRecipe, VPInterleaveEVLRecipe>(
-            EVLRecipe)) {
-      for (unsigned I = 0; I < NumDefVal; ++I) {
-        VPValue *CurVPV = CurRecipe->getVPValue(I);
-        CurVPV->replaceAllUsesWith(EVLRecipe->getVPValue(I));
-      }
-    }
-    ToErase.push_back(CurRecipe);
-  }
-  // Remove dead EVL mask.
-  if (EVLMask->getNumUsers() == 0)
-    ToErase.push_back(EVLMask->getDefiningRecipe());
-
-  for (VPRecipeBase *R : reverse(ToErase)) {
-    SmallVector<VPValue *> PossiblyDead(R->operands());
-    R->eraseFromParent();
-    for (VPValue *Op : PossiblyDead)
-      recursivelyDeleteDeadRecipes(Op);
-  }
 }
 
 /// Add a VPEVLBasedIVPHIRecipe and related recipes to \p Plan and
@@ -2842,7 +2835,7 @@ void VPlanTransforms::addExplicitVectorLength(
       DebugLoc::getCompilerGenerated(), "avl.next");
   AVLPhi->addOperand(NextAVL);
 
-  transformRecipestoEVLRecipes(Plan, *VPEVL);
+  fixupVFUsersForEVL(Plan, *VPEVL);
 
   // Replace all uses of VPCanonicalIVPHIRecipe by
   // VPEVLBasedIVPHIRecipe except for the canonical IV increment.

llvm/lib/Transforms/Vectorize/VPlanTransforms.h

@@ -377,6 +377,17 @@ struct VPlanTransforms {
   /// users in the original exit block using the VPIRInstruction wrapping to the
   /// LCSSA phi.
   static void addExitUsersForFirstOrderRecurrences(VPlan &Plan, VFRange &Range);
+
+  /// If the loop is EVL tail folded, try and optimize any recipes that use a
+  /// EVL based header mask to a VP intrinsic, e.g:
+  ///
+  /// %mask = icmp step-vector, EVL
+  /// %load = load %ptr, %mask
+  ///
+  /// ->
+  ///
+  /// %load = vp.load %ptr, EVL
+  static void optimizeMasksToEVL(VPlan &Plan);
 };
 
 } // namespace llvm

llvm/lib/Transforms/Vectorize/VPlanVerifier.cpp

@@ -317,6 +317,12 @@ bool VPlanVerifier::verifyVPBasicBlock(const VPBasicBlock *VPBB) {
         break;
       }
     }
+    if (const auto *EVLPhi = dyn_cast<VPEVLBasedIVPHIRecipe>(&R)) {
+      if (!isa<VPCanonicalIVPHIRecipe>(std::prev(EVLPhi->getIterator()))) {
+        errs() << "EVL-based IV is not immediately after canonical IV\n";
+        return false;
+      }
+    }
   }
 
   auto *IRBB = dyn_cast<VPIRBasicBlock>(VPBB);

llvm/test/Transforms/LoopVectorize/RISCV/dead-ops-cost.ll

@@ -361,12 +361,12 @@ define void @gather_interleave_group_with_dead_insert_pos(i64 %N, ptr noalias %s
 ; CHECK-NEXT:    [[EVL_BASED_IV:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_EVL_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <vscale x 4 x i64> [ [[INDUCTION]], %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[AVL:%.*]] = phi i64 [ [[TMP2]], %[[VECTOR_PH]] ], [ [[AVL_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[OFFSET_IDX:%.*]] = mul i64 [[EVL_BASED_IV]], 2
 ; CHECK-NEXT:    [[TMP10:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 4, i1 true)
 ; CHECK-NEXT:    [[TMP16:%.*]] = zext i32 [[TMP10]] to i64
 ; CHECK-NEXT:    [[TMP12:%.*]] = mul i64 2, [[TMP16]]
 ; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <vscale x 4 x i64> poison, i64 [[TMP12]], 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:    [[OFFSET_IDX:%.*]] = mul i64 [[EVL_BASED_IV]], 2
 ; CHECK-NEXT:    [[TMP22:%.*]] = getelementptr i8, ptr [[SRC]], i64 [[OFFSET_IDX]]
 ; CHECK-NEXT:    [[INTERLEAVE_EVL:%.*]] = mul nuw nsw i32 [[TMP10]], 2
 ; CHECK-NEXT:    [[WIDE_MASKED_VEC:%.*]] = call <vscale x 8 x i8> @llvm.vp.load.nxv8i8.p0(ptr align 1 [[TMP22]], <vscale x 8 x i1> splat (i1 true), i32 [[INTERLEAVE_EVL]])

llvm/test/Transforms/LoopVectorize/RISCV/divrem.ll

@@ -270,6 +270,7 @@ define void @predicated_udiv(ptr noalias nocapture %a, i64 %v, i64 %n) {
 ; CHECK:       vector.ph:
 ; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <vscale x 2 x i64> poison, i64 [[V:%.*]], i64 0
 ; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <vscale x 2 x i64> [[BROADCAST_SPLATINSERT]], <vscale x 2 x i64> poison, <vscale x 2 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP7:%.*]] = call <vscale x 2 x i32> @llvm.stepvector.nxv2i32()
 ; CHECK-NEXT:    [[TMP6:%.*]] = icmp ne <vscale x 2 x i64> [[BROADCAST_SPLAT]], zeroinitializer
 ; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; CHECK:       vector.body:
@@ -278,7 +279,6 @@ define void @predicated_udiv(ptr noalias nocapture %a, i64 %v, i64 %n) {
 ; CHECK-NEXT:    [[TMP12:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 2, i1 true)
 ; CHECK-NEXT:    [[BROADCAST_SPLATINSERT1:%.*]] = insertelement <vscale x 2 x i32> poison, i32 [[TMP12]], i64 0
 ; CHECK-NEXT:    [[BROADCAST_SPLAT2:%.*]] = shufflevector <vscale x 2 x i32> [[BROADCAST_SPLATINSERT1]], <vscale x 2 x i32> poison, <vscale x 2 x i32> zeroinitializer
-; CHECK-NEXT:    [[TMP7:%.*]] = call <vscale x 2 x i32> @llvm.stepvector.nxv2i32()
 ; CHECK-NEXT:    [[TMP15:%.*]] = icmp ult <vscale x 2 x i32> [[TMP7]], [[BROADCAST_SPLAT2]]
 ; CHECK-NEXT:    [[TMP8:%.*]] = getelementptr inbounds i64, ptr [[A:%.*]], i64 [[INDEX]]
 ; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = call <vscale x 2 x i64> @llvm.vp.load.nxv2i64.p0(ptr align 8 [[TMP8]], <vscale x 2 x i1> splat (i1 true), i32 [[TMP12]])
@@ -354,6 +354,7 @@ define void @predicated_sdiv(ptr noalias nocapture %a, i64 %v, i64 %n) {
 ; CHECK:       vector.ph:
 ; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <vscale x 2 x i64> poison, i64 [[V:%.*]], i64 0
 ; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <vscale x 2 x i64> [[BROADCAST_SPLATINSERT]], <vscale x 2 x i64> poison, <vscale x 2 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP7:%.*]] = call <vscale x 2 x i32> @llvm.stepvector.nxv2i32()
 ; CHECK-NEXT:    [[TMP6:%.*]] = icmp ne <vscale x 2 x i64> [[BROADCAST_SPLAT]], zeroinitializer
 ; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; CHECK:       vector.body:
@@ -362,7 +363,6 @@ define void @predicated_sdiv(ptr noalias nocapture %a, i64 %v, i64 %n) {
 ; CHECK-NEXT:    [[TMP12:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 2, i1 true)
 ; CHECK-NEXT:    [[BROADCAST_SPLATINSERT1:%.*]] = insertelement <vscale x 2 x i32> poison, i32 [[TMP12]], i64 0
 ; CHECK-NEXT:    [[BROADCAST_SPLAT2:%.*]] = shufflevector <vscale x 2 x i32> [[BROADCAST_SPLATINSERT1]], <vscale x 2 x i32> poison, <vscale x 2 x i32> zeroinitializer
-; CHECK-NEXT:    [[TMP7:%.*]] = call <vscale x 2 x i32> @llvm.stepvector.nxv2i32()
 ; CHECK-NEXT:    [[TMP15:%.*]] = icmp ult <vscale x 2 x i32> [[TMP7]], [[BROADCAST_SPLAT2]]
 ; CHECK-NEXT:    [[TMP8:%.*]] = getelementptr inbounds i64, ptr [[A:%.*]], i64 [[INDEX]]
 ; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = call <vscale x 2 x i64> @llvm.vp.load.nxv2i64.p0(ptr align 8 [[TMP8]], <vscale x 2 x i1> splat (i1 true), i32 [[TMP12]])
@@ -576,14 +576,14 @@ define void @predicated_sdiv_by_minus_one(ptr noalias nocapture %a, i64 %n) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[VECTOR_PH:%.*]]
 ; CHECK:       vector.ph:
+; CHECK-NEXT:    [[TMP6:%.*]] = call <vscale x 16 x i32> @llvm.stepvector.nxv16i32()
 ; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; CHECK:       vector.body:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[AVL:%.*]] = phi i64 [ 1024, [[VECTOR_PH]] ], [ [[AVL_NEXT:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP12:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 [[AVL]], i32 16, i1 true)
 ; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <vscale x 16 x i32> poison, i32 [[TMP12]], i64 0
 ; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <vscale x 16 x i32> [[BROADCAST_SPLATINSERT]], <vscale x 16 x i32> poison, <vscale x 16 x i32> zeroinitializer
-; CHECK-NEXT:    [[TMP6:%.*]] = call <vscale x 16 x i32> @llvm.stepvector.nxv16i32()
 ; CHECK-NEXT:    [[TMP15:%.*]] = icmp ult <vscale x 16 x i32> [[TMP6]], [[BROADCAST_SPLAT]]
 ; CHECK-NEXT:    [[TMP7:%.*]] = getelementptr inbounds i8, ptr [[A:%.*]], i64 [[INDEX]]
 ; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = call <vscale x 16 x i8> @llvm.vp.load.nxv16i8.p0(ptr align 1 [[TMP7]], <vscale x 16 x i1> splat (i1 true), i32 [[TMP12]])

llvm/test/Transforms/LoopVectorize/RISCV/reg-usage-bf16.ll

@@ -5,7 +5,7 @@ define void @add(ptr noalias nocapture readonly %src1, ptr noalias nocapture rea
 ; CHECK-LABEL: add
 ; CHECK:       LV(REG): VF = vscale x 4
 ; CHECK-NEXT:  LV(REG): Found max usage: 2 item
-; CHECK-NEXT:  LV(REG): RegisterClass: RISCV::GPRRC, 6 registers
+; CHECK-NEXT:  LV(REG): RegisterClass: RISCV::GPRRC, 5 registers
 ; CHECK-NEXT:  LV(REG): RegisterClass: RISCV::VRRC, 4 registers
 ; CHECK-NEXT:  LV(REG): Found invariant usage: 1 item
 ; CHECK-NEXT:  LV(REG): RegisterClass: RISCV::GPRRC, 1 registers

llvm/test/Transforms/LoopVectorize/RISCV/reg-usage-f16.ll

@@ -6,14 +6,14 @@ define void @add(ptr noalias nocapture readonly %src1, ptr noalias nocapture rea
 ; ZVFH-LABEL: add
 ; ZVFH:       LV(REG): VF = vscale x 4
 ; ZVFH-NEXT:  LV(REG): Found max usage: 2 item
-; ZVFH-NEXT:  LV(REG): RegisterClass: RISCV::GPRRC, 6 registers
+; ZVFH-NEXT:  LV(REG): RegisterClass: RISCV::GPRRC, 5 registers
 ; ZVFH-NEXT:  LV(REG): RegisterClass: RISCV::VRRC, 2 registers
 ; ZVFH-NEXT:  LV(REG): Found invariant usage: 1 item
 ; ZVFH-NEXT:  LV(REG): RegisterClass: RISCV::GPRRC, 1 registers
 ; ZVFHMIN-LABEL: add
 ; ZVFHMIN:       LV(REG): VF = vscale x 4
 ; ZVFHMIN-NEXT:  LV(REG): Found max usage: 2 item
-; ZVFHMIN-NEXT:  LV(REG): RegisterClass: RISCV::GPRRC, 6 registers
+; ZVFHMIN-NEXT:  LV(REG): RegisterClass: RISCV::GPRRC, 5 registers
 ; ZVFHMIN-NEXT:  LV(REG): RegisterClass: RISCV::VRRC, 4 registers
 ; ZVFHMIN-NEXT:  LV(REG): Found invariant usage: 1 item
 ; ZVFHMIN-NEXT:  LV(REG): RegisterClass: RISCV::GPRRC, 1 registers

llvm/test/Transforms/LoopVectorize/RISCV/reg-usage-maxbandwidth.ll

@@ -4,7 +4,7 @@
 define i32 @dotp(ptr %a, ptr %b) {
 ; CHECK-REGS-VP:      LV(REG): VF = vscale x 16
 ; CHECK-REGS-VP-NEXT: LV(REG): Found max usage: 2 item
-; CHECK-REGS-VP-NEXT: LV(REG): RegisterClass: RISCV::GPRRC, 6 registers
+; CHECK-REGS-VP-NEXT: LV(REG): RegisterClass: RISCV::GPRRC, 5 registers
 ; CHECK-REGS-VP-NEXT: LV(REG): RegisterClass: RISCV::VRRC, 24 registers
 ; CHECK-REGS-VP-NEXT: LV(REG): Found invariant usage: 1 item
 ; CHECK-REGS-VP-NEXT: LV(REG): RegisterClass: RISCV::GPRRC, 1 registers