Reapply "[VPlan] Compute cost of more replicating loads/stores in ::computeCost. (#160053)" (#161724)

This reverts commit f61be43.

Recommit a small fix handling scalarization overhead consistently with
legacy cost model if a load is used directly as operand of another
memory operation, which fixes
#161404.

Original message:
Update VPReplicateRecipe::computeCost to compute costs of more
replicating loads/stores.

There are 2 cases that require extra checks to match the legacy cost
model:
1. If the pointer is based on an induction, the legacy cost model passes
its SCEV to getAddressComputationCost. In those cases, still fall back
to the legacy cost. SCEV computations will be added as follow-up
2. If a load is used as part of an address of another load, the legacy
cost model skips the scalarization overhead. Those cases are currently
handled by a usedByLoadOrStore helper.

Note that getScalarizationOverhead also needs updating, because when the
legacy cost model computes the scalarization overhead, scalars have not
been collected yet, so we can't each for replicating recipes to skip
their cost, except other loads. This again can be further improved by
modeling inserts/extracts explicitly and consistently, and compute costs
for those operations directly where needed.

PR: #160053

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -3903,7 +3903,8 @@ void LoopVectorizationPlanner::emitInvalidCostRemarks(
       if (VF.isScalar())
         continue;
 
-      VPCostContext CostCtx(CM.TTI, *CM.TLI, *Plan, CM, CM.CostKind);
+      VPCostContext CostCtx(CM.TTI, *CM.TLI, *Plan, CM, CM.CostKind,
+                            *CM.PSE.getSE());
       precomputeCosts(*Plan, VF, CostCtx);
       auto Iter = vp_depth_first_deep(Plan->getVectorLoopRegion()->getEntry());
       for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(Iter)) {
@@ -4160,7 +4161,8 @@ VectorizationFactor LoopVectorizationPlanner::selectVectorizationFactor() {
 
       // Add on other costs that are modelled in VPlan, but not in the legacy
       // cost model.
-      VPCostContext CostCtx(CM.TTI, *CM.TLI, *P, CM, CM.CostKind);
+      VPCostContext CostCtx(CM.TTI, *CM.TLI, *P, CM, CM.CostKind,
+                            *CM.PSE.getSE());
       VPRegionBlock *VectorRegion = P->getVectorLoopRegion();
       assert(VectorRegion && "Expected to have a vector region!");
       for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
@@ -6852,7 +6854,7 @@ LoopVectorizationPlanner::precomputeCosts(VPlan &Plan, ElementCount VF,
 
 InstructionCost LoopVectorizationPlanner::cost(VPlan &Plan,
                                                ElementCount VF) const {
-  VPCostContext CostCtx(CM.TTI, *CM.TLI, Plan, CM, CM.CostKind);
+  VPCostContext CostCtx(CM.TTI, *CM.TLI, Plan, CM, CM.CostKind, *PSE.getSE());
   InstructionCost Cost = precomputeCosts(Plan, VF, CostCtx);
 
   // Now compute and add the VPlan-based cost.
@@ -7085,7 +7087,8 @@ VectorizationFactor LoopVectorizationPlanner::computeBestVF() {
   // simplifications not accounted for in the legacy cost model. If that's the
   // case, don't trigger the assertion, as the extra simplifications may cause a
   // different VF to be picked by the VPlan-based cost model.
-  VPCostContext CostCtx(CM.TTI, *CM.TLI, BestPlan, CM, CM.CostKind);
+  VPCostContext CostCtx(CM.TTI, *CM.TLI, BestPlan, CM, CM.CostKind,
+                        *CM.PSE.getSE());
   precomputeCosts(BestPlan, BestFactor.Width, CostCtx);
   // Verify that the VPlan-based and legacy cost models agree, except for VPlans
   // with early exits and plans with additional VPlan simplifications. The
@@ -8621,7 +8624,8 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(
   // TODO: Enable following transform when the EVL-version of extended-reduction
   // and mulacc-reduction are implemented.
   if (!CM.foldTailWithEVL()) {
-    VPCostContext CostCtx(CM.TTI, *CM.TLI, *Plan, CM, CM.CostKind);
+    VPCostContext CostCtx(CM.TTI, *CM.TLI, *Plan, CM, CM.CostKind,
+                          *CM.PSE.getSE());
     VPlanTransforms::runPass(VPlanTransforms::convertToAbstractRecipes, *Plan,
                              CostCtx, Range);
   }
@@ -10075,7 +10079,7 @@ bool LoopVectorizePass::processLoop(Loop *L) {
     bool ForceVectorization =
         Hints.getForce() == LoopVectorizeHints::FK_Enabled;
     VPCostContext CostCtx(CM.TTI, *CM.TLI, LVP.getPlanFor(VF.Width), CM,
-                          CM.CostKind);
+                          CM.CostKind, *CM.PSE.getSE());
     if (!ForceVectorization &&
         !isOutsideLoopWorkProfitable(Checks, VF, L, PSE, CostCtx,
                                      LVP.getPlanFor(VF.Width), SEL,

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -1772,7 +1772,8 @@ VPCostContext::getOperandInfo(VPValue *V) const {
 }
 
 InstructionCost VPCostContext::getScalarizationOverhead(
-    Type *ResultTy, ArrayRef<const VPValue *> Operands, ElementCount VF) {
+    Type *ResultTy, ArrayRef<const VPValue *> Operands, ElementCount VF,
+    bool AlwaysIncludeReplicatingR) {
   if (VF.isScalar())
     return 0;
 
@@ -1792,7 +1793,11 @@ InstructionCost VPCostContext::getScalarizationOverhead(
   SmallPtrSet<const VPValue *, 4> UniqueOperands;
   SmallVector<Type *> Tys;
   for (auto *Op : Operands) {
-    if (Op->isLiveIn() || isa<VPReplicateRecipe, VPPredInstPHIRecipe>(Op) ||
+    if (Op->isLiveIn() ||
+        (!AlwaysIncludeReplicatingR &&
+         isa<VPReplicateRecipe, VPPredInstPHIRecipe>(Op)) ||
+        (isa<VPReplicateRecipe>(Op) &&
+         cast<VPReplicateRecipe>(Op)->getOpcode() == Instruction::Load) ||
         !UniqueOperands.insert(Op).second)
       continue;
     Tys.push_back(toVectorizedTy(Types.inferScalarType(Op), VF));

llvm/lib/Transforms/Vectorize/VPlanHelpers.h

@@ -349,12 +349,14 @@ struct VPCostContext {
   LoopVectorizationCostModel &CM;
   SmallPtrSet<Instruction *, 8> SkipCostComputation;
   TargetTransformInfo::TargetCostKind CostKind;
+  ScalarEvolution &SE;
 
   VPCostContext(const TargetTransformInfo &TTI, const TargetLibraryInfo &TLI,
                 const VPlan &Plan, LoopVectorizationCostModel &CM,
-                TargetTransformInfo::TargetCostKind CostKind)
+                TargetTransformInfo::TargetCostKind CostKind,
+                ScalarEvolution &SE)
       : TTI(TTI), TLI(TLI), Types(Plan), LLVMCtx(Plan.getContext()), CM(CM),
-        CostKind(CostKind) {}
+        CostKind(CostKind), SE(SE) {}
 
   /// Return the cost for \p UI with \p VF using the legacy cost model as
   /// fallback until computing the cost of all recipes migrates to VPlan.
@@ -374,10 +376,12 @@ struct VPCostContext {
 
   /// Estimate the overhead of scalarizing a recipe with result type \p ResultTy
   /// and \p Operands with \p VF. This is a convenience wrapper for the
-  /// type-based getScalarizationOverhead API.
-  InstructionCost getScalarizationOverhead(Type *ResultTy,
-                                           ArrayRef<const VPValue *> Operands,
-                                           ElementCount VF);
+  /// type-based getScalarizationOverhead API. If \p AlwaysIncludeReplicatingR
+  /// is true, always compute the cost of scalarizing replicating operands.
+  InstructionCost
+  getScalarizationOverhead(Type *ResultTy, ArrayRef<const VPValue *> Operands,
+                           ElementCount VF,
+                           bool AlwaysIncludeReplicatingR = false);
 };
 
 /// This class can be used to assign names to VPValues. For VPValues without

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -40,6 +40,7 @@
 #include <cassert>
 
 using namespace llvm;
+using namespace llvm::VPlanPatternMatch;
 
 using VectorParts = SmallVector<Value *, 2>;
 
@@ -303,7 +304,6 @@ VPPartialReductionRecipe::computeCost(ElementCount VF,
   VPRecipeBase *OpR = Op->getDefiningRecipe();
 
   // If the partial reduction is predicated, a select will be operand 0
-  using namespace llvm::VPlanPatternMatch;
   if (match(getOperand(1), m_Select(m_VPValue(), m_VPValue(Op), m_VPValue()))) {
     OpR = Op->getDefiningRecipe();
   }
@@ -1963,7 +1963,6 @@ InstructionCost VPWidenSelectRecipe::computeCost(ElementCount VF,
   Type *VectorTy = toVectorTy(Ctx.Types.inferScalarType(this), VF);
 
   VPValue *Op0, *Op1;
-  using namespace llvm::VPlanPatternMatch;
   if (!ScalarCond && ScalarTy->getScalarSizeInBits() == 1 &&
       (match(this, m_LogicalAnd(m_VPValue(Op0), m_VPValue(Op1))) ||
        match(this, m_LogicalOr(m_VPValue(Op0), m_VPValue(Op1))))) {
@@ -3111,6 +3110,62 @@ bool VPReplicateRecipe::shouldPack() const {
   });
 }
 
+/// Returns true if \p Ptr is a pointer computation for which the legacy cost
+/// model computes a SCEV expression when computing the address cost.
+static bool shouldUseAddressAccessSCEV(const VPValue *Ptr) {
+  auto *PtrR = Ptr->getDefiningRecipe();
+  if (!PtrR || !((isa<VPReplicateRecipe>(PtrR) &&
+                  cast<VPReplicateRecipe>(PtrR)->getOpcode() ==
+                      Instruction::GetElementPtr) ||
+                 isa<VPWidenGEPRecipe>(PtrR) ||
+                 match(Ptr, m_GetElementPtr(m_VPValue(), m_VPValue()))))
+    return false;
+
+  // We are looking for a GEP where all indices are either loop invariant or
+  // inductions.
+  for (VPValue *Opd : drop_begin(PtrR->operands())) {
+    if (!Opd->isDefinedOutsideLoopRegions() &&
+        !isa<VPScalarIVStepsRecipe, VPWidenIntOrFpInductionRecipe>(Opd))
+      return false;
+  }
+
+  return true;
+}
+
+/// Returns true if \p V is used as part of the address of another load or
+/// store.
+static bool isUsedByLoadStoreAddress(const VPUser *V) {
+  SmallPtrSet<const VPUser *, 4> Seen;
+  SmallVector<const VPUser *> WorkList = {V};
+
+  while (!WorkList.empty()) {
+    auto *Cur = dyn_cast<VPSingleDefRecipe>(WorkList.pop_back_val());
+    if (!Cur || !Seen.insert(Cur).second)
+      continue;
+
+    for (VPUser *U : Cur->users()) {
+      if (auto *InterleaveR = dyn_cast<VPInterleaveBase>(U))
+        if (InterleaveR->getAddr() == Cur)
+          return true;
+      if (auto *RepR = dyn_cast<VPReplicateRecipe>(U)) {
+        if (RepR->getOpcode() == Instruction::Load &&
+            RepR->getOperand(0) == Cur)
+          return true;
+        if (RepR->getOpcode() == Instruction::Store &&
+            RepR->getOperand(1) == Cur)
+          return true;
+      }
+      if (auto *MemR = dyn_cast<VPWidenMemoryRecipe>(U)) {
+        if (MemR->getAddr() == Cur && MemR->isConsecutive())
+          return true;
+      }
+    }
+
+    append_range(WorkList, cast<VPSingleDefRecipe>(Cur)->users());
+  }
+  return false;
+}
+
 InstructionCost VPReplicateRecipe::computeCost(ElementCount VF,
                                                VPCostContext &Ctx) const {
   Instruction *UI = cast<Instruction>(getUnderlyingValue());
@@ -3218,21 +3273,58 @@ InstructionCost VPReplicateRecipe::computeCost(ElementCount VF,
   }
   case Instruction::Load:
   case Instruction::Store: {
-    if (isSingleScalar()) {
-      bool IsLoad = UI->getOpcode() == Instruction::Load;
-      Type *ValTy = Ctx.Types.inferScalarType(IsLoad ? this : getOperand(0));
-      Type *ScalarPtrTy = Ctx.Types.inferScalarType(getOperand(IsLoad ? 0 : 1));
-      const Align Alignment = getLoadStoreAlignment(UI);
-      unsigned AS = getLoadStoreAddressSpace(UI);
-      TTI::OperandValueInfo OpInfo = TTI::getOperandInfo(UI->getOperand(0));
-      InstructionCost ScalarMemOpCost = Ctx.TTI.getMemoryOpCost(
-          UI->getOpcode(), ValTy, Alignment, AS, Ctx.CostKind, OpInfo, UI);
-      return ScalarMemOpCost + Ctx.TTI.getAddressComputationCost(
-                                   ScalarPtrTy, nullptr, nullptr, Ctx.CostKind);
-    }
+    if (VF.isScalable() && !isSingleScalar())
+      return InstructionCost::getInvalid();
+
     // TODO: See getMemInstScalarizationCost for how to handle replicating and
     // predicated cases.
-    break;
+    const VPRegionBlock *ParentRegion = getParent()->getParent();
+    if (ParentRegion && ParentRegion->isReplicator())
+      break;
+
+    bool IsLoad = UI->getOpcode() == Instruction::Load;
+    const VPValue *PtrOp = getOperand(!IsLoad);
+    // TODO: Handle cases where we need to pass a SCEV to
+    // getAddressComputationCost.
+    if (shouldUseAddressAccessSCEV(PtrOp))
+      break;
+
+    Type *ValTy = Ctx.Types.inferScalarType(IsLoad ? this : getOperand(0));
+    Type *ScalarPtrTy = Ctx.Types.inferScalarType(PtrOp);
+    const Align Alignment = getLoadStoreAlignment(UI);
+    unsigned AS = getLoadStoreAddressSpace(UI);
+    TTI::OperandValueInfo OpInfo = TTI::getOperandInfo(UI->getOperand(0));
+    InstructionCost ScalarMemOpCost = Ctx.TTI.getMemoryOpCost(
+        UI->getOpcode(), ValTy, Alignment, AS, Ctx.CostKind, OpInfo);
+
+    Type *PtrTy = isSingleScalar() ? ScalarPtrTy : toVectorTy(ScalarPtrTy, VF);
+
+    InstructionCost ScalarCost =
+        ScalarMemOpCost + Ctx.TTI.getAddressComputationCost(
+                              PtrTy, &Ctx.SE, nullptr, Ctx.CostKind);
+    if (isSingleScalar())
+      return ScalarCost;
+
+    SmallVector<const VPValue *> OpsToScalarize;
+    Type *ResultTy = Type::getVoidTy(PtrTy->getContext());
+    // Set ResultTy and OpsToScalarize, if scalarization is needed. Currently we
+    // don't assign scalarization overhead in general, if the target prefers
+    // vectorized addressing or the loaded value is used as part of an address
+    // of another load or store.
+    bool PreferVectorizedAddressing = Ctx.TTI.prefersVectorizedAddressing();
+    if (PreferVectorizedAddressing || !isUsedByLoadStoreAddress(this)) {
+      bool EfficientVectorLoadStore =
+          Ctx.TTI.supportsEfficientVectorElementLoadStore();
+      if (!(IsLoad && !PreferVectorizedAddressing) &&
+          !(!IsLoad && EfficientVectorLoadStore))
+        append_range(OpsToScalarize, operands());
+
+      if (!EfficientVectorLoadStore)
+        ResultTy = Ctx.Types.inferScalarType(this);
+    }
+
+    return (ScalarCost * VF.getFixedValue()) +
+           Ctx.getScalarizationOverhead(ResultTy, OpsToScalarize, VF, true);
   }
   }