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llvm-project/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
Florian Hahn e329b68413
[VPlan] Factor out logic to check if recipe is dead (NFCI). 
In preparation to use the helper in more places.
2024-04-03 14:22:41 +01:00

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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 "VPRecipeBuilder.h"
#include "VPlanAnalysis.h"
#include "VPlanCFG.h"
#include "VPlanDominatorTree.h"
#include "VPlanPatternMatch.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/IVDescriptors.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/PatternMatch.h"
using namespace llvm;
void VPlanTransforms::VPInstructionsToVPRecipes(
VPlanPtr &Plan,
function_ref<const InductionDescriptor *(PHINode *)>
GetIntOrFpInductionDescriptor,
ScalarEvolution &SE, const TargetLibraryInfo &TLI) {
ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<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());
VPRecipeBase *NewRecipe = nullptr;
if (auto *VPPhi = dyn_cast<VPWidenPHIRecipe>(&Ingredient)) {
auto *Phi = cast<PHINode>(VPPhi->getUnderlyingValue());
const auto *II = GetIntOrFpInductionDescriptor(Phi);
if (!II)
continue;
VPValue *Start = Plan->getOrAddLiveIn(II->getStartValue());
VPValue *Step =
vputils::getOrCreateVPValueForSCEVExpr(*Plan, II->getStep(), SE);
NewRecipe = new VPWidenIntOrFpInductionRecipe(Phi, Start, Step, *II);
} 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, Ingredient.getOperand(0), nullptr /*Mask*/,
false /*Consecutive*/, false /*Reverse*/,
Ingredient.getDebugLoc());
} else if (StoreInst *Store = dyn_cast<StoreInst>(Inst)) {
NewRecipe = new VPWidenMemoryInstructionRecipe(
*Store, Ingredient.getOperand(1), Ingredient.getOperand(0),
nullptr /*Mask*/, false /*Consecutive*/, false /*Reverse*/,
Ingredient.getDebugLoc());
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
NewRecipe = new VPWidenGEPRecipe(GEP, Ingredient.operands());
} else if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
NewRecipe = new VPWidenCallRecipe(
*CI, drop_end(Ingredient.operands()),
getVectorIntrinsicIDForCall(CI, &TLI), CI->getDebugLoc());
} else if (SelectInst *SI = dyn_cast<SelectInst>(Inst)) {
NewRecipe = new VPWidenSelectRecipe(*SI, Ingredient.operands());
} else if (auto *CI = dyn_cast<CastInst>(Inst)) {
NewRecipe = new VPWidenCastRecipe(
CI->getOpcode(), Ingredient.getOperand(0), CI->getType(), *CI);
} else {
NewRecipe = new VPWidenRecipe(*Inst, Ingredient.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();
}
}
}
static bool sinkScalarOperands(VPlan &Plan) {
auto Iter = vp_depth_first_deep(Plan.getEntry());
bool Changed = false;
// First, collect the operands of all recipes in replicate blocks as seeds for
// sinking.
SetVector<std::pair<VPBasicBlock *, VPSingleDefRecipe *>> WorkList;
for (VPRegionBlock *VPR : VPBlockUtils::blocksOnly<VPRegionBlock>(Iter)) {
VPBasicBlock *EntryVPBB = VPR->getEntryBasicBlock();
if (!VPR->isReplicator() || EntryVPBB->getSuccessors().size() != 2)
continue;
VPBasicBlock *VPBB = dyn_cast<VPBasicBlock>(EntryVPBB->getSuccessors()[0]);
if (!VPBB || VPBB->getSingleSuccessor() != VPR->getExitingBasicBlock())
continue;
for (auto &Recipe : *VPBB) {
for (VPValue *Op : Recipe.operands())
if (auto *Def =
dyn_cast_or_null<VPSingleDefRecipe>(Op->getDefiningRecipe()))
WorkList.insert(std::make_pair(VPBB, Def));
}
}
bool ScalarVFOnly = Plan.hasScalarVFOnly();
// Try to sink each replicate or scalar IV steps recipe in the worklist.
for (unsigned I = 0; I != WorkList.size(); ++I) {
VPBasicBlock *SinkTo;
VPSingleDefRecipe *SinkCandidate;
std::tie(SinkTo, SinkCandidate) = WorkList[I];
if (SinkCandidate->getParent() == SinkTo ||
SinkCandidate->mayHaveSideEffects() ||
SinkCandidate->mayReadOrWriteMemory())
continue;
if (auto *RepR = dyn_cast<VPReplicateRecipe>(SinkCandidate)) {
if (!ScalarVFOnly && 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);
// We only know how to duplicate VPRecipeRecipes for now.
return NeedsDuplicating && isa<VPReplicateRecipe>(SinkCandidate);
};
if (!all_of(SinkCandidate->users(), CanSinkWithUser))
continue;
if (NeedsDuplicating) {
if (ScalarVFOnly)
continue;
Instruction *I = SinkCandidate->getUnderlyingInstr();
auto *Clone = new VPReplicateRecipe(I, SinkCandidate->operands(), true);
// TODO: add ".cloned" suffix to name of Clone's VPValue.
Clone->insertBefore(SinkCandidate);
SinkCandidate->replaceUsesWithIf(Clone, [SinkTo](VPUser &U, unsigned) {
return cast<VPRecipeBase>(&U)->getParent() != SinkTo;
});
}
SinkCandidate->moveBefore(*SinkTo, SinkTo->getFirstNonPhi());
for (VPValue *Op : SinkCandidate->operands())
if (auto *Def =
dyn_cast_or_null<VPSingleDefRecipe>(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;
}
// Merge replicate regions in their successor region, if a replicate region
// is connected to a successor replicate region with the same predicate by a
// single, empty VPBasicBlock.
static bool mergeReplicateRegionsIntoSuccessors(VPlan &Plan) {
SetVector<VPRegionBlock *> DeletedRegions;
// Collect replicate regions followed by an empty block, followed by another
// replicate region with matching masks to process front. This is to avoid
// iterator invalidation issues while merging regions.
SmallVector<VPRegionBlock *, 8> WorkList;
for (VPRegionBlock *Region1 : VPBlockUtils::blocksOnly<VPRegionBlock>(
vp_depth_first_deep(Plan.getEntry()))) {
if (!Region1->isReplicator())
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 || !Region2->isReplicator())
continue;
VPValue *Mask1 = getPredicatedMask(Region1);
VPValue *Mask2 = getPredicatedMask(Region2);
if (!Mask1 || Mask1 != Mask2)
continue;
assert(Mask1 && Mask2 && "both region must have conditions");
WorkList.push_back(Region1);
}
// Move recipes from Region1 to its successor region, if both are triangles.
for (VPRegionBlock *Region1 : WorkList) {
if (DeletedRegions.contains(Region1))
continue;
auto *MiddleBasicBlock = cast<VPBasicBlock>(Region1->getSingleSuccessor());
auto *Region2 = cast<VPRegionBlock>(MiddleBasicBlock->getSingleSuccessor());
VPBasicBlock *Then1 = getPredicatedThenBlock(Region1);
VPBasicBlock *Then2 = getPredicatedThenBlock(Region2);
if (!Then1 || !Then2)
continue;
// 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();
Phi1ToMoveV->replaceUsesWithIf(PredInst1, [Then2](VPUser &U, unsigned) {
auto *UI = dyn_cast<VPRecipeBase>(&U);
return UI && UI->getParent() == Then2;
});
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 !DeletedRegions.empty();
}
static VPRegionBlock *createReplicateRegion(VPReplicateRecipe *PredRecipe,
VPlan &Plan) {
Instruction *Instr = PredRecipe->getUnderlyingInstr();
// Build the triangular if-then region.
std::string RegionName = (Twine("pred.") + Instr->getOpcodeName()).str();
assert(Instr->getParent() && "Predicated instruction not in any basic block");
auto *BlockInMask = PredRecipe->getMask();
auto *BOMRecipe = new VPBranchOnMaskRecipe(BlockInMask);
auto *Entry = new VPBasicBlock(Twine(RegionName) + ".entry", BOMRecipe);
// Replace predicated replicate recipe with a replicate recipe without a
// mask but in the replicate region.
auto *RecipeWithoutMask = new VPReplicateRecipe(
PredRecipe->getUnderlyingInstr(),
make_range(PredRecipe->op_begin(), std::prev(PredRecipe->op_end())),
PredRecipe->isUniform());
auto *Pred = new VPBasicBlock(Twine(RegionName) + ".if", RecipeWithoutMask);
VPPredInstPHIRecipe *PHIRecipe = nullptr;
if (PredRecipe->getNumUsers() != 0) {
PHIRecipe = new VPPredInstPHIRecipe(RecipeWithoutMask);
PredRecipe->replaceAllUsesWith(PHIRecipe);
PHIRecipe->setOperand(0, RecipeWithoutMask);
}
PredRecipe->eraseFromParent();
auto *Exiting = new VPBasicBlock(Twine(RegionName) + ".continue", PHIRecipe);
VPRegionBlock *Region = new VPRegionBlock(Entry, Exiting, RegionName, true);
// Note: first set Entry as region entry and then connect successors starting
// from it in order, to propagate the "parent" of each VPBasicBlock.
VPBlockUtils::insertTwoBlocksAfter(Pred, Exiting, Entry);
VPBlockUtils::connectBlocks(Pred, Exiting);
return Region;
}
static void addReplicateRegions(VPlan &Plan) {
SmallVector<VPReplicateRecipe *> WorkList;
for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
vp_depth_first_deep(Plan.getEntry()))) {
for (VPRecipeBase &R : *VPBB)
if (auto *RepR = dyn_cast<VPReplicateRecipe>(&R)) {
if (RepR->isPredicated())
WorkList.push_back(RepR);
}
}
unsigned BBNum = 0;
for (VPReplicateRecipe *RepR : WorkList) {
VPBasicBlock *CurrentBlock = RepR->getParent();
VPBasicBlock *SplitBlock = CurrentBlock->splitAt(RepR->getIterator());
BasicBlock *OrigBB = RepR->getUnderlyingInstr()->getParent();
SplitBlock->setName(
OrigBB->hasName() ? OrigBB->getName() + "." + Twine(BBNum++) : "");
// Record predicated instructions for above packing optimizations.
VPBlockBase *Region = createReplicateRegion(RepR, Plan);
Region->setParent(CurrentBlock->getParent());
VPBlockUtils::disconnectBlocks(CurrentBlock, SplitBlock);
VPBlockUtils::connectBlocks(CurrentBlock, Region);
VPBlockUtils::connectBlocks(Region, SplitBlock);
}
}
/// Remove redundant VPBasicBlocks by merging them into their predecessor if
/// the predecessor has a single successor.
static bool mergeBlocksIntoPredecessors(VPlan &Plan) {
SmallVector<VPBasicBlock *> WorkList;
for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
vp_depth_first_deep(Plan.getEntry()))) {
auto *PredVPBB =
dyn_cast_or_null<VPBasicBlock>(VPBB->getSinglePredecessor());
if (PredVPBB && PredVPBB->getNumSuccessors() == 1)
WorkList.push_back(VPBB);
}
for (VPBasicBlock *VPBB : WorkList) {
VPBasicBlock *PredVPBB = cast<VPBasicBlock>(VPBB->getSinglePredecessor());
for (VPRecipeBase &R : make_early_inc_range(*VPBB))
R.moveBefore(*PredVPBB, PredVPBB->end());
VPBlockUtils::disconnectBlocks(PredVPBB, VPBB);
auto *ParentRegion = cast_or_null<VPRegionBlock>(VPBB->getParent());
if (ParentRegion && ParentRegion->getExiting() == VPBB)
ParentRegion->setExiting(PredVPBB);
for (auto *Succ : to_vector(VPBB->successors())) {
VPBlockUtils::disconnectBlocks(VPBB, Succ);
VPBlockUtils::connectBlocks(PredVPBB, Succ);
}
delete VPBB;
}
return !WorkList.empty();
}
void VPlanTransforms::createAndOptimizeReplicateRegions(VPlan &Plan) {
// Convert masked VPReplicateRecipes to if-then region blocks.
addReplicateRegions(Plan);
bool ShouldSimplify = true;
while (ShouldSimplify) {
ShouldSimplify = sinkScalarOperands(Plan);
ShouldSimplify |= mergeReplicateRegionsIntoSuccessors(Plan);
ShouldSimplify |= mergeBlocksIntoPredecessors(Plan);
}
}
/// Remove redundant casts of inductions.
///
/// Such redundant casts are casts of induction variables that can be ignored,
/// because we already proved that the casted phi is equal to the uncasted phi
/// in the vectorized loop. There is no need to vectorize the cast - the same
/// value can be used for both the phi and casts in the vector loop.
static void 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)) {
VPSingleDefRecipe *FoundUserCast = nullptr;
for (auto *U : FindMyCast->users()) {
auto *UserCast = dyn_cast<VPSingleDefRecipe>(U);
if (UserCast && UserCast->getUnderlyingValue() == IRCast) {
FoundUserCast = UserCast;
break;
}
}
FindMyCast = FoundUserCast;
}
FindMyCast->replaceAllUsesWith(IV);
}
}
/// Try to replace VPWidenCanonicalIVRecipes with a widened canonical IV
/// recipe, if it exists.
static void 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 (any_of(WidenOriginalIV->users(),
[WidenOriginalIV](VPUser *U) {
return !U->usesScalars(WidenOriginalIV);
}) ||
vputils::onlyFirstLaneUsed(WidenNewIV)) {
WidenNewIV->replaceAllUsesWith(WidenOriginalIV);
WidenNewIV->eraseFromParent();
return;
}
}
}
/// Returns true if \p R is dead and can be removed.
static bool isDeadRecipe(VPRecipeBase &R) {
using namespace llvm::PatternMatch;
// Do remove conditional assume instructions as their conditions may be
// flattened.
auto *RepR = dyn_cast<VPReplicateRecipe>(&R);
bool IsConditionalAssume =
RepR && RepR->isPredicated() &&
match(RepR->getUnderlyingInstr(), m_Intrinsic<Intrinsic::assume>());
if (IsConditionalAssume)
return true;
if (R.mayHaveSideEffects())
return false;
// Recipe is dead if no user keeps the recipe alive.
return all_of(R.definedValues(),
[](VPValue *V) { return V->getNumUsers() == 0; });
}
static void removeDeadRecipes(VPlan &Plan) {
ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<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 (isDeadRecipe(R))
R.eraseFromParent();
}
}
}
static VPValue *createScalarIVSteps(VPlan &Plan,
InductionDescriptor::InductionKind Kind,
Instruction::BinaryOps InductionOpcode,
FPMathOperator *FPBinOp,
ScalarEvolution &SE, Instruction *TruncI,
VPValue *StartV, VPValue *Step,
VPBasicBlock::iterator IP) {
VPBasicBlock *HeaderVPBB = Plan.getVectorLoopRegion()->getEntryBasicBlock();
VPCanonicalIVPHIRecipe *CanonicalIV = Plan.getCanonicalIV();
VPSingleDefRecipe *BaseIV = CanonicalIV;
if (!CanonicalIV->isCanonical(Kind, StartV, Step)) {
BaseIV = new VPDerivedIVRecipe(Kind, FPBinOp, StartV, CanonicalIV, Step);
HeaderVPBB->insert(BaseIV, IP);
}
// Truncate base induction if needed.
VPTypeAnalysis TypeInfo(Plan.getCanonicalIV()->getScalarType(),
SE.getContext());
Type *ResultTy = TypeInfo.inferScalarType(BaseIV);
if (TruncI) {
Type *TruncTy = TruncI->getType();
assert(ResultTy->getScalarSizeInBits() > TruncTy->getScalarSizeInBits() &&
"Not truncating.");
assert(ResultTy->isIntegerTy() && "Truncation requires an integer type");
BaseIV = new VPScalarCastRecipe(Instruction::Trunc, BaseIV, TruncTy);
HeaderVPBB->insert(BaseIV, IP);
ResultTy = TruncTy;
}
// Truncate step if needed.
Type *StepTy = TypeInfo.inferScalarType(Step);
if (ResultTy != StepTy) {
assert(StepTy->getScalarSizeInBits() > ResultTy->getScalarSizeInBits() &&
"Not truncating.");
assert(StepTy->isIntegerTy() && "Truncation requires an integer type");
Step = new VPScalarCastRecipe(Instruction::Trunc, Step, ResultTy);
auto *VecPreheader =
cast<VPBasicBlock>(HeaderVPBB->getSingleHierarchicalPredecessor());
VecPreheader->appendRecipe(Step->getDefiningRecipe());
}
VPScalarIVStepsRecipe *Steps = new VPScalarIVStepsRecipe(
BaseIV, Step, InductionOpcode,
FPBinOp ? FPBinOp->getFastMathFlags() : FastMathFlags());
HeaderVPBB->insert(Steps, IP);
return Steps;
}
/// Legalize VPWidenPointerInductionRecipe, by replacing it with a PtrAdd
/// (IndStart, ScalarIVSteps (0, Step)) if only its scalar values are used, as
/// VPWidenPointerInductionRecipe will generate vectors only. If some users
/// require vectors while other require scalars, the scalar uses need to extract
/// the scalars from the generated vectors (Note that this is different to how
/// int/fp inductions are handled). Also optimize VPWidenIntOrFpInductionRecipe,
/// if any of its users needs scalar values, by providing them scalar steps
/// built on the canonical scalar IV and update the original IV's users. This is
/// an optional optimization to reduce the needs of vector extracts.
static void legalizeAndOptimizeInductions(VPlan &Plan, ScalarEvolution &SE) {
SmallVector<VPRecipeBase *> ToRemove;
VPBasicBlock *HeaderVPBB = Plan.getVectorLoopRegion()->getEntryBasicBlock();
bool HasOnlyVectorVFs = !Plan.hasVF(ElementCount::getFixed(1));
VPBasicBlock::iterator InsertPt = HeaderVPBB->getFirstNonPhi();
for (VPRecipeBase &Phi : HeaderVPBB->phis()) {
// Replace wide pointer inductions which have only their scalars used by
// PtrAdd(IndStart, ScalarIVSteps (0, Step)).
if (auto *PtrIV = dyn_cast<VPWidenPointerInductionRecipe>(&Phi)) {
if (!PtrIV->onlyScalarsGenerated(Plan.hasScalableVF()))
continue;
const InductionDescriptor &ID = PtrIV->getInductionDescriptor();
VPValue *StartV =
Plan.getOrAddLiveIn(ConstantInt::get(ID.getStep()->getType(), 0));
VPValue *StepV = PtrIV->getOperand(1);
VPRecipeBase *Steps =
createScalarIVSteps(Plan, InductionDescriptor::IK_IntInduction,
Instruction::Add, nullptr, SE, nullptr, StartV,
StepV, InsertPt)
->getDefiningRecipe();
auto *Recipe =
new VPInstruction(VPInstruction::PtrAdd,
{PtrIV->getStartValue(), Steps->getVPSingleValue()},
PtrIV->getDebugLoc(), "next.gep");
Recipe->insertAfter(Steps);
PtrIV->replaceAllUsesWith(Recipe);
continue;
}
// Replace widened induction with scalar steps for users that only use
// scalars.
auto *WideIV = dyn_cast<VPWidenIntOrFpInductionRecipe>(&Phi);
if (!WideIV)
continue;
if (HasOnlyVectorVFs && none_of(WideIV->users(), [WideIV](VPUser *U) {
return U->usesScalars(WideIV);
}))
continue;
const InductionDescriptor &ID = WideIV->getInductionDescriptor();
VPValue *Steps = createScalarIVSteps(
Plan, ID.getKind(), ID.getInductionOpcode(),
dyn_cast_or_null<FPMathOperator>(ID.getInductionBinOp()), SE,
WideIV->getTruncInst(), WideIV->getStartValue(), WideIV->getStepValue(),
InsertPt);
// Update scalar users of IV to use Step instead.
if (!HasOnlyVectorVFs)
WideIV->replaceAllUsesWith(Steps);
else
WideIV->replaceUsesWithIf(Steps, [WideIV](VPUser &U, unsigned) {
return U.usesScalars(WideIV);
});
}
}
/// Remove redundant EpxandSCEVRecipes in \p Plan's entry block by replacing
/// them with already existing recipes expanding the same SCEV expression.
static void 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();
}
}
void VPlanTransforms::optimizeForVFAndUF(VPlan &Plan, ElementCount BestVF,
unsigned BestUF,
PredicatedScalarEvolution &PSE) {
assert(Plan.hasVF(BestVF) && "BestVF is not available in Plan");
assert(Plan.hasUF(BestUF) && "BestUF is not available in Plan");
VPBasicBlock *ExitingVPBB =
Plan.getVectorLoopRegion()->getExitingBasicBlock();
auto *Term = &ExitingVPBB->back();
// Try to simplify the branch condition if TC <= VF * UF when preparing to
// execute the plan for the main vector loop. We only do this if the
// terminator is:
// 1. BranchOnCount, or
// 2. BranchOnCond where the input is Not(ActiveLaneMask).
using namespace llvm::VPlanPatternMatch;
if (!match(Term, m_BranchOnCount(m_VPValue(), m_VPValue())) &&
!match(Term,
m_BranchOnCond(m_Not(m_ActiveLaneMask(m_VPValue(), m_VPValue())))))
return;
Type *IdxTy =
Plan.getCanonicalIV()->getStartValue()->getLiveInIRValue()->getType();
const SCEV *TripCount = createTripCountSCEV(IdxTy, PSE);
ScalarEvolution &SE = *PSE.getSE();
ElementCount NumElements = BestVF.multiplyCoefficientBy(BestUF);
const SCEV *C = SE.getElementCount(TripCount->getType(), NumElements);
if (TripCount->isZero() ||
!SE.isKnownPredicate(CmpInst::ICMP_ULE, TripCount, C))
return;
LLVMContext &Ctx = SE.getContext();
auto *BOC =
new VPInstruction(VPInstruction::BranchOnCond,
{Plan.getOrAddLiveIn(ConstantInt::getTrue(Ctx))});
Term->eraseFromParent();
ExitingVPBB->appendRecipe(BOC);
Plan.setVF(BestVF);
Plan.setUF(BestUF);
// TODO: Further simplifications are possible
// 1. Replace inductions with constants.
// 2. Replace vector loop region with VPBasicBlock.
}
#ifndef NDEBUG
static VPRegionBlock *GetReplicateRegion(VPRecipeBase *R) {
auto *Region = dyn_cast_or_null<VPRegionBlock>(R->getParent()->getParent());
if (Region && Region->isReplicator()) {
assert(Region->getNumSuccessors() == 1 &&
Region->getNumPredecessors() == 1 && "Expected SESE region!");
assert(R->getParent()->size() == 1 &&
"A recipe in an original replicator region must be the only "
"recipe in its block");
return Region;
}
return nullptr;
}
#endif
static bool properlyDominates(const VPRecipeBase *A, const VPRecipeBase *B,
VPDominatorTree &VPDT) {
if (A == B)
return false;
auto LocalComesBefore = [](const VPRecipeBase *A, const VPRecipeBase *B) {
for (auto &R : *A->getParent()) {
if (&R == A)
return true;
if (&R == B)
return false;
}
llvm_unreachable("recipe not found");
};
const VPBlockBase *ParentA = A->getParent();
const VPBlockBase *ParentB = B->getParent();
if (ParentA == ParentB)
return LocalComesBefore(A, B);
assert(!GetReplicateRegion(const_cast<VPRecipeBase *>(A)) &&
"No replicate regions expected at this point");
assert(!GetReplicateRegion(const_cast<VPRecipeBase *>(B)) &&
"No replicate regions expected at this point");
return VPDT.properlyDominates(ParentA, ParentB);
}
/// Sink users of \p FOR after the recipe defining the previous value \p
/// Previous of the recurrence. \returns true if all users of \p FOR could be
/// re-arranged as needed or false if it is not possible.
static bool
sinkRecurrenceUsersAfterPrevious(VPFirstOrderRecurrencePHIRecipe *FOR,
VPRecipeBase *Previous,
VPDominatorTree &VPDT) {
// Collect recipes that need sinking.
SmallVector<VPRecipeBase *> WorkList;
SmallPtrSet<VPRecipeBase *, 8> Seen;
Seen.insert(Previous);
auto TryToPushSinkCandidate = [&](VPRecipeBase *SinkCandidate) {
// The previous value must not depend on the users of the recurrence phi. In
// that case, FOR is not a fixed order recurrence.
if (SinkCandidate == Previous)
return false;
if (isa<VPHeaderPHIRecipe>(SinkCandidate) ||
!Seen.insert(SinkCandidate).second ||
properlyDominates(Previous, SinkCandidate, VPDT))
return true;
if (SinkCandidate->mayHaveSideEffects())
return false;
WorkList.push_back(SinkCandidate);
return true;
};
// Recursively sink users of FOR after Previous.
WorkList.push_back(FOR);
for (unsigned I = 0; I != WorkList.size(); ++I) {
VPRecipeBase *Current = WorkList[I];
assert(Current->getNumDefinedValues() == 1 &&
"only recipes with a single defined value expected");
for (VPUser *User : Current->getVPSingleValue()->users()) {
if (auto *R = dyn_cast<VPRecipeBase>(User))
if (!TryToPushSinkCandidate(R))
return false;
}
}
// Keep recipes to sink ordered by dominance so earlier instructions are
// processed first.
sort(WorkList, [&VPDT](const VPRecipeBase *A, const VPRecipeBase *B) {
return properlyDominates(A, B, VPDT);
});
for (VPRecipeBase *SinkCandidate : WorkList) {
if (SinkCandidate == FOR)
continue;
SinkCandidate->moveAfter(Previous);
Previous = SinkCandidate;
}
return true;
}
bool VPlanTransforms::adjustFixedOrderRecurrences(VPlan &Plan,
VPBuilder &Builder) {
VPDominatorTree VPDT;
VPDT.recalculate(Plan);
SmallVector<VPFirstOrderRecurrencePHIRecipe *> RecurrencePhis;
for (VPRecipeBase &R :
Plan.getVectorLoopRegion()->getEntry()->getEntryBasicBlock()->phis())
if (auto *FOR = dyn_cast<VPFirstOrderRecurrencePHIRecipe>(&R))
RecurrencePhis.push_back(FOR);
for (VPFirstOrderRecurrencePHIRecipe *FOR : RecurrencePhis) {
SmallPtrSet<VPFirstOrderRecurrencePHIRecipe *, 4> SeenPhis;
VPRecipeBase *Previous = FOR->getBackedgeValue()->getDefiningRecipe();
// Fixed-order recurrences do not contain cycles, so this loop is guaranteed
// to terminate.
while (auto *PrevPhi =
dyn_cast_or_null<VPFirstOrderRecurrencePHIRecipe>(Previous)) {
assert(PrevPhi->getParent() == FOR->getParent());
assert(SeenPhis.insert(PrevPhi).second);
Previous = PrevPhi->getBackedgeValue()->getDefiningRecipe();
}
if (!sinkRecurrenceUsersAfterPrevious(FOR, Previous, VPDT))
return false;
// Introduce a recipe to combine the incoming and previous values of a
// fixed-order recurrence.
VPBasicBlock *InsertBlock = Previous->getParent();
if (isa<VPHeaderPHIRecipe>(Previous))
Builder.setInsertPoint(InsertBlock, InsertBlock->getFirstNonPhi());
else
Builder.setInsertPoint(InsertBlock, std::next(Previous->getIterator()));
auto *RecurSplice = cast<VPInstruction>(
Builder.createNaryOp(VPInstruction::FirstOrderRecurrenceSplice,
{FOR, FOR->getBackedgeValue()}));
FOR->replaceAllUsesWith(RecurSplice);
// Set the first operand of RecurSplice to FOR again, after replacing
// all users.
RecurSplice->setOperand(0, FOR);
}
return true;
}
void VPlanTransforms::clearReductionWrapFlags(VPlan &Plan) {
for (VPRecipeBase &R :
Plan.getVectorLoopRegion()->getEntryBasicBlock()->phis()) {
auto *PhiR = dyn_cast<VPReductionPHIRecipe>(&R);
if (!PhiR)
continue;
const RecurrenceDescriptor &RdxDesc = PhiR->getRecurrenceDescriptor();
RecurKind RK = RdxDesc.getRecurrenceKind();
if (RK != RecurKind::Add && RK != RecurKind::Mul)
continue;
SmallSetVector<VPValue *, 8> Worklist;
Worklist.insert(PhiR);
for (unsigned I = 0; I != Worklist.size(); ++I) {
VPValue *Cur = Worklist[I];
if (auto *RecWithFlags =
dyn_cast<VPRecipeWithIRFlags>(Cur->getDefiningRecipe())) {
RecWithFlags->dropPoisonGeneratingFlags();
}
for (VPUser *U : Cur->users()) {
auto *UserRecipe = dyn_cast<VPRecipeBase>(U);
if (!UserRecipe)
continue;
for (VPValue *V : UserRecipe->definedValues())
Worklist.insert(V);
}
}
}
}
/// Try to simplify recipe \p R.
static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
// Try to remove redundant blend recipes.
if (auto *Blend = dyn_cast<VPBlendRecipe>(&R)) {
VPValue *Inc0 = Blend->getIncomingValue(0);
for (unsigned I = 1; I != Blend->getNumIncomingValues(); ++I)
if (Inc0 != Blend->getIncomingValue(I))
return;
Blend->replaceAllUsesWith(Inc0);
Blend->eraseFromParent();
return;
}
using namespace llvm::VPlanPatternMatch;
VPValue *A;
if (match(&R, m_Trunc(m_ZExtOrSExt(m_VPValue(A))))) {
VPValue *Trunc = R.getVPSingleValue();
Type *TruncTy = TypeInfo.inferScalarType(Trunc);
Type *ATy = TypeInfo.inferScalarType(A);
if (TruncTy == ATy) {
Trunc->replaceAllUsesWith(A);
} else {
// Don't replace a scalarizing recipe with a widened cast.
if (isa<VPReplicateRecipe>(&R))
return;
if (ATy->getScalarSizeInBits() < TruncTy->getScalarSizeInBits()) {
unsigned ExtOpcode = match(R.getOperand(0), m_SExt(m_VPValue()))
? Instruction::SExt
: Instruction::ZExt;
auto *VPC =
new VPWidenCastRecipe(Instruction::CastOps(ExtOpcode), A, TruncTy);
VPC->insertBefore(&R);
Trunc->replaceAllUsesWith(VPC);
} else if (ATy->getScalarSizeInBits() > TruncTy->getScalarSizeInBits()) {
auto *VPC = new VPWidenCastRecipe(Instruction::Trunc, A, TruncTy);
VPC->insertBefore(&R);
Trunc->replaceAllUsesWith(VPC);
}
}
#ifndef NDEBUG
// Verify that the cached type info is for both A and its users is still
// accurate by comparing it to freshly computed types.
VPTypeAnalysis TypeInfo2(
R.getParent()->getPlan()->getCanonicalIV()->getScalarType(),
TypeInfo.getContext());
assert(TypeInfo.inferScalarType(A) == TypeInfo2.inferScalarType(A));
for (VPUser *U : A->users()) {
auto *R = dyn_cast<VPRecipeBase>(U);
if (!R)
continue;
for (VPValue *VPV : R->definedValues())
assert(TypeInfo.inferScalarType(VPV) == TypeInfo2.inferScalarType(VPV));
}
#endif
}
if (match(&R, m_CombineOr(m_Mul(m_VPValue(A), m_SpecificInt(1)),
m_Mul(m_SpecificInt(1), m_VPValue(A)))))
return R.getVPSingleValue()->replaceAllUsesWith(A);
}
/// Try to simplify the recipes in \p Plan.
static void simplifyRecipes(VPlan &Plan, LLVMContext &Ctx) {
ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<VPBlockBase *>> RPOT(
Plan.getEntry());
VPTypeAnalysis TypeInfo(Plan.getCanonicalIV()->getScalarType(), Ctx);
for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(RPOT)) {
for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
simplifyRecipe(R, TypeInfo);
}
}
}
void VPlanTransforms::truncateToMinimalBitwidths(
VPlan &Plan, const MapVector<Instruction *, uint64_t> &MinBWs,
LLVMContext &Ctx) {
#ifndef NDEBUG
// Count the processed recipes and cross check the count later with MinBWs
// size, to make sure all entries in MinBWs have been handled.
unsigned NumProcessedRecipes = 0;
#endif
// Keep track of created truncates, so they can be re-used. Note that we
// cannot use RAUW after creating a new truncate, as this would could make
// other uses have different types for their operands, making them invalidly
// typed.
DenseMap<VPValue *, VPWidenCastRecipe *> ProcessedTruncs;
VPTypeAnalysis TypeInfo(Plan.getCanonicalIV()->getScalarType(), Ctx);
VPBasicBlock *PH = Plan.getEntry();
for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
vp_depth_first_deep(Plan.getVectorLoopRegion()))) {
for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
if (!isa<VPWidenRecipe, VPWidenCastRecipe, VPReplicateRecipe,
VPWidenSelectRecipe, VPWidenMemoryInstructionRecipe>(&R))
continue;
if (isa<VPWidenMemoryInstructionRecipe>(&R) &&
cast<VPWidenMemoryInstructionRecipe>(&R)->isStore())
continue;
VPValue *ResultVPV = R.getVPSingleValue();
auto *UI = cast_or_null<Instruction>(ResultVPV->getUnderlyingValue());
unsigned NewResSizeInBits = MinBWs.lookup(UI);
if (!NewResSizeInBits)
continue;
#ifndef NDEBUG
NumProcessedRecipes++;
#endif
// If the value wasn't vectorized, we must maintain the original scalar
// type. Skip those here, after incrementing NumProcessedRecipes. Also
// skip casts which do not need to be handled explicitly here, as
// redundant casts will be removed during recipe simplification.
if (isa<VPReplicateRecipe, VPWidenCastRecipe>(&R)) {
#ifndef NDEBUG
// If any of the operands is a live-in and not used by VPWidenRecipe or
// VPWidenSelectRecipe, but in MinBWs, make sure it is counted as
// processed as well. When MinBWs is currently constructed, there is no
// information about whether recipes are widened or replicated and in
// case they are reciplicated the operands are not truncated. Counting
// them them here ensures we do not miss any recipes in MinBWs.
// TODO: Remove once the analysis is done on VPlan.
for (VPValue *Op : R.operands()) {
if (!Op->isLiveIn())
continue;
auto *UV = dyn_cast_or_null<Instruction>(Op->getUnderlyingValue());
if (UV && MinBWs.contains(UV) && !ProcessedTruncs.contains(Op) &&
all_of(Op->users(), [](VPUser *U) {
return !isa<VPWidenRecipe, VPWidenSelectRecipe>(U);
})) {
// Add an entry to ProcessedTruncs to avoid counting the same
// operand multiple times.
ProcessedTruncs[Op] = nullptr;
NumProcessedRecipes += 1;
}
}
#endif
continue;
}
Type *OldResTy = TypeInfo.inferScalarType(ResultVPV);
unsigned OldResSizeInBits = OldResTy->getScalarSizeInBits();
assert(OldResTy->isIntegerTy() && "only integer types supported");
(void)OldResSizeInBits;
auto *NewResTy = IntegerType::get(Ctx, NewResSizeInBits);
// Any wrapping introduced by shrinking this operation shouldn't be
// considered undefined behavior. So, we can't unconditionally copy
// arithmetic wrapping flags to VPW.
if (auto *VPW = dyn_cast<VPRecipeWithIRFlags>(&R))
VPW->dropPoisonGeneratingFlags();
if (OldResSizeInBits != NewResSizeInBits) {
// Extend result to original width.
auto *Ext =
new VPWidenCastRecipe(Instruction::ZExt, ResultVPV, OldResTy);
Ext->insertAfter(&R);
ResultVPV->replaceAllUsesWith(Ext);
Ext->setOperand(0, ResultVPV);
assert(OldResSizeInBits > NewResSizeInBits && "Nothing to shrink?");
} else
assert(cast<VPWidenRecipe>(&R)->getOpcode() == Instruction::ICmp &&
"Only ICmps should not need extending the result.");
if (isa<VPWidenMemoryInstructionRecipe>(&R)) {
assert(!cast<VPWidenMemoryInstructionRecipe>(&R)->isStore() && "stores cannot be narrowed");
continue;
}
// Shrink operands by introducing truncates as needed.
unsigned StartIdx = isa<VPWidenSelectRecipe>(&R) ? 1 : 0;
for (unsigned Idx = StartIdx; Idx != R.getNumOperands(); ++Idx) {
auto *Op = R.getOperand(Idx);
unsigned OpSizeInBits =
TypeInfo.inferScalarType(Op)->getScalarSizeInBits();
if (OpSizeInBits == NewResSizeInBits)
continue;
assert(OpSizeInBits > NewResSizeInBits && "nothing to truncate");
auto [ProcessedIter, IterIsEmpty] =
ProcessedTruncs.insert({Op, nullptr});
VPWidenCastRecipe *NewOp =
IterIsEmpty
? new VPWidenCastRecipe(Instruction::Trunc, Op, NewResTy)
: ProcessedIter->second;
R.setOperand(Idx, NewOp);
if (!IterIsEmpty)
continue;
ProcessedIter->second = NewOp;
if (!Op->isLiveIn()) {
NewOp->insertBefore(&R);
} else {
PH->appendRecipe(NewOp);
#ifndef NDEBUG
auto *OpInst = dyn_cast<Instruction>(Op->getLiveInIRValue());
bool IsContained = MinBWs.contains(OpInst);
NumProcessedRecipes += IsContained;
#endif
}
}
}
}
assert(MinBWs.size() == NumProcessedRecipes &&
"some entries in MinBWs haven't been processed");
}
void VPlanTransforms::optimize(VPlan &Plan, ScalarEvolution &SE) {
removeRedundantCanonicalIVs(Plan);
removeRedundantInductionCasts(Plan);
simplifyRecipes(Plan, SE.getContext());
legalizeAndOptimizeInductions(Plan, SE);
removeDeadRecipes(Plan);
createAndOptimizeReplicateRegions(Plan);
removeRedundantExpandSCEVRecipes(Plan);
mergeBlocksIntoPredecessors(Plan);
}
// Add a VPActiveLaneMaskPHIRecipe and related recipes to \p Plan and replace
// the loop terminator with a branch-on-cond recipe with the negated
// active-lane-mask as operand. Note that this turns the loop into an
// uncountable one. Only the existing terminator is replaced, all other existing
// recipes/users remain unchanged, except for poison-generating flags being
// dropped from the canonical IV increment. Return the created
// VPActiveLaneMaskPHIRecipe.
//
// The function uses the following definitions:
//
// %TripCount = DataWithControlFlowWithoutRuntimeCheck ?
// calculate-trip-count-minus-VF (original TC) : original TC
// %IncrementValue = DataWithControlFlowWithoutRuntimeCheck ?
// CanonicalIVPhi : CanonicalIVIncrement
// %StartV is the canonical induction start value.
//
// The function adds the following recipes:
//
// vector.ph:
// %TripCount = calculate-trip-count-minus-VF (original TC)
// [if DataWithControlFlowWithoutRuntimeCheck]
// %EntryInc = canonical-iv-increment-for-part %StartV
// %EntryALM = active-lane-mask %EntryInc, %TripCount
//
// vector.body:
// ...
// %P = active-lane-mask-phi [ %EntryALM, %vector.ph ], [ %ALM, %vector.body ]
// ...
// %InLoopInc = canonical-iv-increment-for-part %IncrementValue
// %ALM = active-lane-mask %InLoopInc, TripCount
// %Negated = Not %ALM
// branch-on-cond %Negated
//
static VPActiveLaneMaskPHIRecipe *addVPLaneMaskPhiAndUpdateExitBranch(
VPlan &Plan, bool DataAndControlFlowWithoutRuntimeCheck) {
VPRegionBlock *TopRegion = Plan.getVectorLoopRegion();
VPBasicBlock *EB = TopRegion->getExitingBasicBlock();
auto *CanonicalIVPHI = Plan.getCanonicalIV();
VPValue *StartV = CanonicalIVPHI->getStartValue();
auto *CanonicalIVIncrement =
cast<VPInstruction>(CanonicalIVPHI->getBackedgeValue());
// TODO: Check if dropping the flags is needed if
// !DataAndControlFlowWithoutRuntimeCheck.
CanonicalIVIncrement->dropPoisonGeneratingFlags();
DebugLoc DL = CanonicalIVIncrement->getDebugLoc();
// We can't use StartV directly in the ActiveLaneMask VPInstruction, since
// we have to take unrolling into account. Each part needs to start at
// Part * VF
auto *VecPreheader = cast<VPBasicBlock>(TopRegion->getSinglePredecessor());
VPBuilder Builder(VecPreheader);
// Create the ActiveLaneMask instruction using the correct start values.
VPValue *TC = Plan.getTripCount();
VPValue *TripCount, *IncrementValue;
if (!DataAndControlFlowWithoutRuntimeCheck) {
// When the loop is guarded by a runtime overflow check for the loop
// induction variable increment by VF, we can increment the value before
// the get.active.lane mask and use the unmodified tripcount.
IncrementValue = CanonicalIVIncrement;
TripCount = TC;
} else {
// When avoiding a runtime check, the active.lane.mask inside the loop
// uses a modified trip count and the induction variable increment is
// done after the active.lane.mask intrinsic is called.
IncrementValue = CanonicalIVPHI;
TripCount = Builder.createNaryOp(VPInstruction::CalculateTripCountMinusVF,
{TC}, DL);
}
auto *EntryIncrement = Builder.createOverflowingOp(
VPInstruction::CanonicalIVIncrementForPart, {StartV}, {false, false}, DL,
"index.part.next");
// Create the active lane mask instruction in the VPlan preheader.
auto *EntryALM =
Builder.createNaryOp(VPInstruction::ActiveLaneMask, {EntryIncrement, TC},
DL, "active.lane.mask.entry");
// Now create the ActiveLaneMaskPhi recipe in the main loop using the
// preheader ActiveLaneMask instruction.
auto LaneMaskPhi = new VPActiveLaneMaskPHIRecipe(EntryALM, DebugLoc());
LaneMaskPhi->insertAfter(CanonicalIVPHI);
// Create the active lane mask for the next iteration of the loop before the
// original terminator.
VPRecipeBase *OriginalTerminator = EB->getTerminator();
Builder.setInsertPoint(OriginalTerminator);
auto *InLoopIncrement =
Builder.createOverflowingOp(VPInstruction::CanonicalIVIncrementForPart,
{IncrementValue}, {false, false}, DL);
auto *ALM = Builder.createNaryOp(VPInstruction::ActiveLaneMask,
{InLoopIncrement, TripCount}, DL,
"active.lane.mask.next");
LaneMaskPhi->addOperand(ALM);
// Replace the original terminator with BranchOnCond. We have to invert the
// mask here because a true condition means jumping to the exit block.
auto *NotMask = Builder.createNot(ALM, DL);
Builder.createNaryOp(VPInstruction::BranchOnCond, {NotMask}, DL);
OriginalTerminator->eraseFromParent();
return LaneMaskPhi;
}
void VPlanTransforms::addActiveLaneMask(
VPlan &Plan, bool UseActiveLaneMaskForControlFlow,
bool DataAndControlFlowWithoutRuntimeCheck) {
assert((!DataAndControlFlowWithoutRuntimeCheck ||
UseActiveLaneMaskForControlFlow) &&
"DataAndControlFlowWithoutRuntimeCheck implies "
"UseActiveLaneMaskForControlFlow");
auto FoundWidenCanonicalIVUser =
find_if(Plan.getCanonicalIV()->users(),
[](VPUser *U) { return isa<VPWidenCanonicalIVRecipe>(U); });
assert(FoundWidenCanonicalIVUser &&
"Must have widened canonical IV when tail folding!");
auto *WideCanonicalIV =
cast<VPWidenCanonicalIVRecipe>(*FoundWidenCanonicalIVUser);
VPSingleDefRecipe *LaneMask;
if (UseActiveLaneMaskForControlFlow) {
LaneMask = addVPLaneMaskPhiAndUpdateExitBranch(
Plan, DataAndControlFlowWithoutRuntimeCheck);
} else {
VPBuilder B = VPBuilder::getToInsertAfter(WideCanonicalIV);
LaneMask = B.createNaryOp(VPInstruction::ActiveLaneMask,
{WideCanonicalIV, Plan.getTripCount()}, nullptr,
"active.lane.mask");
}
// Walk users of WideCanonicalIV and replace all compares of the form
// (ICMP_ULE, WideCanonicalIV, backedge-taken-count) with an
// active-lane-mask.
VPValue *BTC = Plan.getOrCreateBackedgeTakenCount();
for (VPUser *U : SmallVector<VPUser *>(WideCanonicalIV->users())) {
auto *CompareToReplace = dyn_cast<VPInstruction>(U);
if (!CompareToReplace ||
CompareToReplace->getOpcode() != Instruction::ICmp ||
CompareToReplace->getPredicate() != CmpInst::ICMP_ULE ||
CompareToReplace->getOperand(1) != BTC)
continue;
assert(CompareToReplace->getOperand(0) == WideCanonicalIV &&
"WidenCanonicalIV must be the first operand of the compare");
CompareToReplace->replaceAllUsesWith(LaneMask);
CompareToReplace->eraseFromParent();
}
}
void VPlanTransforms::dropPoisonGeneratingRecipes(
VPlan &Plan, function_ref<bool(BasicBlock *)> BlockNeedsPredication) {
// Collect recipes in the backward slice of `Root` that may generate a poison
// value that is used after vectorization.
SmallPtrSet<VPRecipeBase *, 16> Visited;
auto collectPoisonGeneratingInstrsInBackwardSlice([&](VPRecipeBase *Root) {
SmallVector<VPRecipeBase *, 16> Worklist;
Worklist.push_back(Root);
// Traverse the backward slice of Root through its use-def chain.
while (!Worklist.empty()) {
VPRecipeBase *CurRec = Worklist.back();
Worklist.pop_back();
if (!Visited.insert(CurRec).second)
continue;
// Prune search if we find another recipe generating a widen memory
// instruction. Widen memory instructions involved in address computation
// will lead to gather/scatter instructions, which don't need to be
// handled.
if (isa<VPWidenMemoryInstructionRecipe>(CurRec) ||
isa<VPInterleaveRecipe>(CurRec) ||
isa<VPScalarIVStepsRecipe>(CurRec) ||
isa<VPCanonicalIVPHIRecipe>(CurRec) ||
isa<VPActiveLaneMaskPHIRecipe>(CurRec))
continue;
// This recipe contributes to the address computation of a widen
// load/store. If the underlying instruction has poison-generating flags,
// drop them directly.
if (auto *RecWithFlags = dyn_cast<VPRecipeWithIRFlags>(CurRec)) {
VPValue *A, *B;
using namespace llvm::VPlanPatternMatch;
// Dropping disjoint from an OR may yield incorrect results, as some
// analysis may have converted it to an Add implicitly (e.g. SCEV used
// for dependence analysis). Instead, replace it with an equivalent Add.
// This is possible as all users of the disjoint OR only access lanes
// where the operands are disjoint or poison otherwise.
if (match(RecWithFlags, m_Or(m_VPValue(A), m_VPValue(B))) &&
RecWithFlags->isDisjoint()) {
VPBuilder Builder(RecWithFlags);
VPInstruction *New = Builder.createOverflowingOp(
Instruction::Add, {A, B}, {false, false},
RecWithFlags->getDebugLoc());
RecWithFlags->replaceAllUsesWith(New);
RecWithFlags->eraseFromParent();
CurRec = New;
} else
RecWithFlags->dropPoisonGeneratingFlags();
} else {
Instruction *Instr = dyn_cast_or_null<Instruction>(
CurRec->getVPSingleValue()->getUnderlyingValue());
(void)Instr;
assert((!Instr || !Instr->hasPoisonGeneratingFlags()) &&
"found instruction with poison generating flags not covered by "
"VPRecipeWithIRFlags");
}
// Add new definitions to the worklist.
for (VPValue *operand : CurRec->operands())
if (VPRecipeBase *OpDef = operand->getDefiningRecipe())
Worklist.push_back(OpDef);
}
});
// Traverse all the recipes in the VPlan and collect the poison-generating
// recipes in the backward slice starting at the address of a VPWidenRecipe or
// VPInterleaveRecipe.
auto Iter = vp_depth_first_deep(Plan.getEntry());
for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(Iter)) {
for (VPRecipeBase &Recipe : *VPBB) {
if (auto *WidenRec = dyn_cast<VPWidenMemoryInstructionRecipe>(&Recipe)) {
Instruction &UnderlyingInstr = WidenRec->getIngredient();
VPRecipeBase *AddrDef = WidenRec->getAddr()->getDefiningRecipe();
if (AddrDef && WidenRec->isConsecutive() &&
BlockNeedsPredication(UnderlyingInstr.getParent()))
collectPoisonGeneratingInstrsInBackwardSlice(AddrDef);
} else if (auto *InterleaveRec = dyn_cast<VPInterleaveRecipe>(&Recipe)) {
VPRecipeBase *AddrDef = InterleaveRec->getAddr()->getDefiningRecipe();
if (AddrDef) {
// Check if any member of the interleave group needs predication.
const InterleaveGroup<Instruction> *InterGroup =
InterleaveRec->getInterleaveGroup();
bool NeedPredication = false;
for (int I = 0, NumMembers = InterGroup->getNumMembers();
I < NumMembers; ++I) {
Instruction *Member = InterGroup->getMember(I);
if (Member)
NeedPredication |= BlockNeedsPredication(Member->getParent());
}
if (NeedPredication)
collectPoisonGeneratingInstrsInBackwardSlice(AddrDef);
}
}
}
}
}
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