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llvm-project/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

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//===-- VPlanTransforms.cpp - Utility VPlan to VPlan transforms -----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file implements a set of utility VPlan to VPlan transformations.
///
//===----------------------------------------------------------------------===//
#include "VPlanTransforms.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/IVDescriptors.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/Intrinsics.h"
using namespace llvm;
void VPlanTransforms::VPInstructionsToVPRecipes(
Loop *OrigLoop, VPlanPtr &Plan,
function_ref<const InductionDescriptor *(PHINode *)>
GetIntOrFpInductionDescriptor,
SmallPtrSetImpl<Instruction *> &DeadInstructions, ScalarEvolution &SE,
const TargetLibraryInfo &TLI) {
ReversePostOrderTraversal<VPBlockRecursiveTraversalWrapper<VPBlockBase *>>
RPOT(Plan->getEntry());
for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(RPOT)) {
VPRecipeBase *Term = VPBB->getTerminator();
auto EndIter = Term ? Term->getIterator() : VPBB->end();
// Introduce each ingredient into VPlan.
for (VPRecipeBase &Ingredient :
make_early_inc_range(make_range(VPBB->begin(), EndIter))) {
VPValue *VPV = Ingredient.getVPSingleValue();
Instruction *Inst = cast<Instruction>(VPV->getUnderlyingValue());
if (DeadInstructions.count(Inst)) {
VPValue DummyValue;
VPV->replaceAllUsesWith(&DummyValue);
Ingredient.eraseFromParent();
continue;
}
VPRecipeBase *NewRecipe = nullptr;
if (auto *VPPhi = dyn_cast<VPWidenPHIRecipe>(&Ingredient)) {
auto *Phi = cast<PHINode>(VPPhi->getUnderlyingValue());
if (const auto *II = GetIntOrFpInductionDescriptor(Phi)) {
VPValue *Start = Plan->getOrAddVPValue(II->getStartValue());
VPValue *Step =
vputils::getOrCreateVPValueForSCEVExpr(*Plan, II->getStep(), SE);
NewRecipe =
new VPWidenIntOrFpInductionRecipe(Phi, Start, Step, *II, true);
} else {
Plan->addVPValue(Phi, VPPhi);
continue;
}
} else {
assert(isa<VPInstruction>(&Ingredient) &&
"only VPInstructions expected here");
assert(!isa<PHINode>(Inst) && "phis should be handled above");
// Create VPWidenMemoryInstructionRecipe for loads and stores.
if (LoadInst *Load = dyn_cast<LoadInst>(Inst)) {
NewRecipe = new VPWidenMemoryInstructionRecipe(
*Load, Plan->getOrAddVPValue(getLoadStorePointerOperand(Inst)),
nullptr /*Mask*/, false /*Consecutive*/, false /*Reverse*/);
} else if (StoreInst *Store = dyn_cast<StoreInst>(Inst)) {
NewRecipe = new VPWidenMemoryInstructionRecipe(
*Store, Plan->getOrAddVPValue(getLoadStorePointerOperand(Inst)),
Plan->getOrAddVPValue(Store->getValueOperand()), nullptr /*Mask*/,
false /*Consecutive*/, false /*Reverse*/);
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
NewRecipe = new VPWidenGEPRecipe(
GEP, Plan->mapToVPValues(GEP->operands()), OrigLoop);
} else if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
NewRecipe =
new VPWidenCallRecipe(*CI, Plan->mapToVPValues(CI->args()),
getVectorIntrinsicIDForCall(CI, &TLI));
} else if (SelectInst *SI = dyn_cast<SelectInst>(Inst)) {
bool InvariantCond =
SE.isLoopInvariant(SE.getSCEV(SI->getOperand(0)), OrigLoop);
NewRecipe = new VPWidenSelectRecipe(
*SI, Plan->mapToVPValues(SI->operands()), InvariantCond);
} else {
NewRecipe =
new VPWidenRecipe(*Inst, Plan->mapToVPValues(Inst->operands()));
}
}
NewRecipe->insertBefore(&Ingredient);
if (NewRecipe->getNumDefinedValues() == 1)
VPV->replaceAllUsesWith(NewRecipe->getVPSingleValue());
else
assert(NewRecipe->getNumDefinedValues() == 0 &&
"Only recpies with zero or one defined values expected");
Ingredient.eraseFromParent();
Plan->removeVPValueFor(Inst);
for (auto *Def : NewRecipe->definedValues()) {
Plan->addVPValue(Inst, Def);
}
}
}
}
bool VPlanTransforms::sinkScalarOperands(VPlan &Plan) {
auto Iter = depth_first(
VPBlockRecursiveTraversalWrapper<VPBlockBase *>(Plan.getEntry()));
bool Changed = false;
// First, collect the operands of all predicated replicate recipes as seeds
// for sinking.
SetVector<std::pair<VPBasicBlock *, VPRecipeBase *>> WorkList;
for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(Iter)) {
for (auto &Recipe : *VPBB) {
auto *RepR = dyn_cast<VPReplicateRecipe>(&Recipe);
if (!RepR || !RepR->isPredicated())
continue;
for (VPValue *Op : RepR->operands())
if (auto *Def = Op->getDefiningRecipe())
WorkList.insert(std::make_pair(RepR->getParent(), Def));
}
}
// Try to sink each replicate or scalar IV steps recipe in the worklist.
while (!WorkList.empty()) {
VPBasicBlock *SinkTo;
VPRecipeBase *SinkCandidate;
std::tie(SinkTo, SinkCandidate) = WorkList.pop_back_val();
if (SinkCandidate->getParent() == SinkTo ||
SinkCandidate->mayHaveSideEffects() ||
SinkCandidate->mayReadOrWriteMemory())
continue;
if (auto *RepR = dyn_cast<VPReplicateRecipe>(SinkCandidate)) {
if (RepR->isUniform())
continue;
} else if (!isa<VPScalarIVStepsRecipe>(SinkCandidate))
continue;
bool NeedsDuplicating = false;
// All recipe users of the sink candidate must be in the same block SinkTo
// or all users outside of SinkTo must be uniform-after-vectorization (
// i.e., only first lane is used) . In the latter case, we need to duplicate
// SinkCandidate.
auto CanSinkWithUser = [SinkTo, &NeedsDuplicating,
SinkCandidate](VPUser *U) {
auto *UI = dyn_cast<VPRecipeBase>(U);
if (!UI)
return false;
if (UI->getParent() == SinkTo)
return true;
NeedsDuplicating =
UI->onlyFirstLaneUsed(SinkCandidate->getVPSingleValue());
// We only know how to duplicate VPRecipeRecipes for now.
return NeedsDuplicating && isa<VPReplicateRecipe>(SinkCandidate);
};
if (!all_of(SinkCandidate->getVPSingleValue()->users(), CanSinkWithUser))
continue;
if (NeedsDuplicating) {
Instruction *I = cast<Instruction>(
cast<VPReplicateRecipe>(SinkCandidate)->getUnderlyingValue());
auto *Clone =
new VPReplicateRecipe(I, SinkCandidate->operands(), true, false);
// TODO: add ".cloned" suffix to name of Clone's VPValue.
Clone->insertBefore(SinkCandidate);
SmallVector<VPUser *, 4> Users(
SinkCandidate->getVPSingleValue()->users());
for (auto *U : Users) {
auto *UI = cast<VPRecipeBase>(U);
if (UI->getParent() == SinkTo)
continue;
for (unsigned Idx = 0; Idx != UI->getNumOperands(); Idx++) {
if (UI->getOperand(Idx) != SinkCandidate->getVPSingleValue())
continue;
UI->setOperand(Idx, Clone);
}
}
}
SinkCandidate->moveBefore(*SinkTo, SinkTo->getFirstNonPhi());
for (VPValue *Op : SinkCandidate->operands())
if (auto *Def = Op->getDefiningRecipe())
WorkList.insert(std::make_pair(SinkTo, Def));
Changed = true;
}
return Changed;
}
/// If \p R is a region with a VPBranchOnMaskRecipe in the entry block, return
/// the mask.
VPValue *getPredicatedMask(VPRegionBlock *R) {
auto *EntryBB = dyn_cast<VPBasicBlock>(R->getEntry());
if (!EntryBB || EntryBB->size() != 1 ||
!isa<VPBranchOnMaskRecipe>(EntryBB->begin()))
return nullptr;
return cast<VPBranchOnMaskRecipe>(&*EntryBB->begin())->getOperand(0);
}
/// If \p R is a triangle region, return the 'then' block of the triangle.
static VPBasicBlock *getPredicatedThenBlock(VPRegionBlock *R) {
auto *EntryBB = cast<VPBasicBlock>(R->getEntry());
if (EntryBB->getNumSuccessors() != 2)
return nullptr;
auto *Succ0 = dyn_cast<VPBasicBlock>(EntryBB->getSuccessors()[0]);
auto *Succ1 = dyn_cast<VPBasicBlock>(EntryBB->getSuccessors()[1]);
if (!Succ0 || !Succ1)
return nullptr;
if (Succ0->getNumSuccessors() + Succ1->getNumSuccessors() != 1)
return nullptr;
if (Succ0->getSingleSuccessor() == Succ1)
return Succ0;
if (Succ1->getSingleSuccessor() == Succ0)
return Succ1;
return nullptr;
}
bool VPlanTransforms::mergeReplicateRegions(VPlan &Plan) {
SetVector<VPRegionBlock *> DeletedRegions;
bool Changed = false;
// Collect region blocks to process up-front, to avoid iterator invalidation
// issues while merging regions.
SmallVector<VPRegionBlock *, 8> CandidateRegions(
VPBlockUtils::blocksOnly<VPRegionBlock>(depth_first(
VPBlockRecursiveTraversalWrapper<VPBlockBase *>(Plan.getEntry()))));
// Check if Base is a predicated triangle, followed by an empty block,
// followed by another predicate triangle. If that's the case, move the
// recipes from the first to the second triangle.
for (VPRegionBlock *Region1 : CandidateRegions) {
if (DeletedRegions.contains(Region1))
continue;
auto *MiddleBasicBlock =
dyn_cast_or_null<VPBasicBlock>(Region1->getSingleSuccessor());
if (!MiddleBasicBlock || !MiddleBasicBlock->empty())
continue;
auto *Region2 =
dyn_cast_or_null<VPRegionBlock>(MiddleBasicBlock->getSingleSuccessor());
if (!Region2)
continue;
VPValue *Mask1 = getPredicatedMask(Region1);
VPValue *Mask2 = getPredicatedMask(Region2);
if (!Mask1 || Mask1 != Mask2)
continue;
VPBasicBlock *Then1 = getPredicatedThenBlock(Region1);
VPBasicBlock *Then2 = getPredicatedThenBlock(Region2);
if (!Then1 || !Then2)
continue;
assert(Mask1 && Mask2 && "both region must have conditions");
// Note: No fusion-preventing memory dependencies are expected in either
// region. Such dependencies should be rejected during earlier dependence
// checks, which guarantee accesses can be re-ordered for vectorization.
//
// Move recipes to the successor region.
for (VPRecipeBase &ToMove : make_early_inc_range(reverse(*Then1)))
ToMove.moveBefore(*Then2, Then2->getFirstNonPhi());
auto *Merge1 = cast<VPBasicBlock>(Then1->getSingleSuccessor());
auto *Merge2 = cast<VPBasicBlock>(Then2->getSingleSuccessor());
// Move VPPredInstPHIRecipes from the merge block to the successor region's
// merge block. Update all users inside the successor region to use the
// original values.
for (VPRecipeBase &Phi1ToMove : make_early_inc_range(reverse(*Merge1))) {
VPValue *PredInst1 =
cast<VPPredInstPHIRecipe>(&Phi1ToMove)->getOperand(0);
VPValue *Phi1ToMoveV = Phi1ToMove.getVPSingleValue();
SmallVector<VPUser *> Users(Phi1ToMoveV->users());
for (VPUser *U : Users) {
auto *UI = dyn_cast<VPRecipeBase>(U);
if (!UI || UI->getParent() != Then2)
continue;
for (unsigned I = 0, E = U->getNumOperands(); I != E; ++I) {
if (Phi1ToMoveV != U->getOperand(I))
continue;
U->setOperand(I, PredInst1);
}
}
Phi1ToMove.moveBefore(*Merge2, Merge2->begin());
}
// Finally, remove the first region.
for (VPBlockBase *Pred : make_early_inc_range(Region1->getPredecessors())) {
VPBlockUtils::disconnectBlocks(Pred, Region1);
VPBlockUtils::connectBlocks(Pred, MiddleBasicBlock);
}
VPBlockUtils::disconnectBlocks(Region1, MiddleBasicBlock);
DeletedRegions.insert(Region1);
}
for (VPRegionBlock *ToDelete : DeletedRegions)
delete ToDelete;
return Changed;
}
void VPlanTransforms::removeRedundantInductionCasts(VPlan &Plan) {
for (auto &Phi : Plan.getVectorLoopRegion()->getEntryBasicBlock()->phis()) {
auto *IV = dyn_cast<VPWidenIntOrFpInductionRecipe>(&Phi);
if (!IV || IV->getTruncInst())
continue;
// A sequence of IR Casts has potentially been recorded for IV, which
// *must be bypassed* when the IV is vectorized, because the vectorized IV
// will produce the desired casted value. This sequence forms a def-use
// chain and is provided in reverse order, ending with the cast that uses
// the IV phi. Search for the recipe of the last cast in the chain and
// replace it with the original IV. Note that only the final cast is
// expected to have users outside the cast-chain and the dead casts left
// over will be cleaned up later.
auto &Casts = IV->getInductionDescriptor().getCastInsts();
VPValue *FindMyCast = IV;
for (Instruction *IRCast : reverse(Casts)) {
VPRecipeBase *FoundUserCast = nullptr;
for (auto *U : FindMyCast->users()) {
auto *UserCast = cast<VPRecipeBase>(U);
if (UserCast->getNumDefinedValues() == 1 &&
UserCast->getVPSingleValue()->getUnderlyingValue() == IRCast) {
FoundUserCast = UserCast;
break;
}
}
FindMyCast = FoundUserCast->getVPSingleValue();
}
FindMyCast->replaceAllUsesWith(IV);
}
}
void VPlanTransforms::removeRedundantCanonicalIVs(VPlan &Plan) {
VPCanonicalIVPHIRecipe *CanonicalIV = Plan.getCanonicalIV();
VPWidenCanonicalIVRecipe *WidenNewIV = nullptr;
for (VPUser *U : CanonicalIV->users()) {
WidenNewIV = dyn_cast<VPWidenCanonicalIVRecipe>(U);
if (WidenNewIV)
break;
}
if (!WidenNewIV)
return;
VPBasicBlock *HeaderVPBB = Plan.getVectorLoopRegion()->getEntryBasicBlock();
for (VPRecipeBase &Phi : HeaderVPBB->phis()) {
auto *WidenOriginalIV = dyn_cast<VPWidenIntOrFpInductionRecipe>(&Phi);
if (!WidenOriginalIV || !WidenOriginalIV->isCanonical() ||
WidenOriginalIV->getScalarType() != WidenNewIV->getScalarType())
continue;
// Replace WidenNewIV with WidenOriginalIV if WidenOriginalIV provides
// everything WidenNewIV's users need. That is, WidenOriginalIV will
// generate a vector phi or all users of WidenNewIV demand the first lane
// only.
if (WidenOriginalIV->needsVectorIV() ||
vputils::onlyFirstLaneUsed(WidenNewIV)) {
WidenNewIV->replaceAllUsesWith(WidenOriginalIV);
WidenNewIV->eraseFromParent();
return;
}
}
}
void VPlanTransforms::removeDeadRecipes(VPlan &Plan) {
ReversePostOrderTraversal<VPBlockRecursiveTraversalWrapper<VPBlockBase *>>
RPOT(Plan.getEntry());
for (VPBasicBlock *VPBB : reverse(VPBlockUtils::blocksOnly<VPBasicBlock>(RPOT))) {
// The recipes in the block are processed in reverse order, to catch chains
// of dead recipes.
for (VPRecipeBase &R : make_early_inc_range(reverse(*VPBB))) {
if (R.mayHaveSideEffects() || any_of(R.definedValues(), [](VPValue *V) {
return V->getNumUsers() > 0;
}))
continue;
R.eraseFromParent();
}
}
}
void VPlanTransforms::optimizeInductions(VPlan &Plan, ScalarEvolution &SE) {
SmallVector<VPRecipeBase *> ToRemove;
VPBasicBlock *HeaderVPBB = Plan.getVectorLoopRegion()->getEntryBasicBlock();
bool HasOnlyVectorVFs = !Plan.hasVF(ElementCount::getFixed(1));
for (VPRecipeBase &Phi : HeaderVPBB->phis()) {
auto *WideIV = dyn_cast<VPWidenIntOrFpInductionRecipe>(&Phi);
if (!WideIV)
continue;
if (HasOnlyVectorVFs && none_of(WideIV->users(), [WideIV](VPUser *U) {
return U->usesScalars(WideIV);
}))
continue;
auto IP = HeaderVPBB->getFirstNonPhi();
VPCanonicalIVPHIRecipe *CanonicalIV = Plan.getCanonicalIV();
Type *ResultTy = WideIV->getPHINode()->getType();
if (Instruction *TruncI = WideIV->getTruncInst())
ResultTy = TruncI->getType();
const InductionDescriptor &ID = WideIV->getInductionDescriptor();
VPValue *Step =
vputils::getOrCreateVPValueForSCEVExpr(Plan, ID.getStep(), SE);
VPValue *BaseIV = CanonicalIV;
if (!CanonicalIV->isCanonical(ID, ResultTy)) {
BaseIV = new VPDerivedIVRecipe(ID, WideIV->getStartValue(), CanonicalIV,
Step, ResultTy);
HeaderVPBB->insert(BaseIV->getDefiningRecipe(), IP);
}
VPScalarIVStepsRecipe *Steps = new VPScalarIVStepsRecipe(ID, BaseIV, Step);
HeaderVPBB->insert(Steps, IP);
// Update scalar users of IV to use Step instead. Use SetVector to ensure
// the list of users doesn't contain duplicates.
SetVector<VPUser *> Users(WideIV->user_begin(), WideIV->user_end());
for (VPUser *U : Users) {
if (HasOnlyVectorVFs && !U->usesScalars(WideIV))
continue;
for (unsigned I = 0, E = U->getNumOperands(); I != E; I++) {
if (U->getOperand(I) != WideIV)
continue;
U->setOperand(I, Steps);
}
}
}
}
void VPlanTransforms::removeRedundantExpandSCEVRecipes(VPlan &Plan) {
DenseMap<const SCEV *, VPValue *> SCEV2VPV;
for (VPRecipeBase &R :
make_early_inc_range(*Plan.getEntry()->getEntryBasicBlock())) {
auto *ExpR = dyn_cast<VPExpandSCEVRecipe>(&R);
if (!ExpR)
continue;
auto I = SCEV2VPV.insert({ExpR->getSCEV(), ExpR});
if (I.second)
continue;
ExpR->replaceAllUsesWith(I.first->second);
ExpR->eraseFromParent();
}
}
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