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llvm-mirror/lib/Transforms/Scalar/LoopDistribute.cpp
Florian Hahn cea367bb2a [LoopVersion] Unify SCEVChecks and alias check handling (NFC). 
This is an initial cleanup of the way LoopVersioning interacts with LAA.

Currently LoopVersioning has 2 ways of initializing things:

1. Passing LAI and passing UseLAIChecks = true
2. Passing UseLAIChecks = false, followed by calling setSCEVChecks and
   setAliasChecks.

Both ways of initializing lead to the same result and the duplication
seems more complicated than necessary.

This patch removes the UseLAIChecks flag from the constructor and the
setSCEVChecks & setAliasChecks helpers and move initialization
exclusively to the constructor.

This simplifies things, by providing a single way to initialize
LoopVersioning and reducing duplication.

Reviewed By: Meinersbur, lebedev.ri

Differential Revision: https://reviews.llvm.org/D84406
2020-10-15 22:02:17 +01:00

1088 lines
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//===- LoopDistribute.cpp - Loop Distribution Pass ------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements the Loop Distribution Pass. Its main focus is to
// distribute loops that cannot be vectorized due to dependence cycles. It
// tries to isolate the offending dependences into a new loop allowing
// vectorization of the remaining parts.
//
// For dependence analysis, the pass uses the LoopVectorizer's
// LoopAccessAnalysis. Because this analysis presumes no change in the order of
// memory operations, special care is taken to preserve the lexical order of
// these operations.
//
// Similarly to the Vectorizer, the pass also supports loop versioning to
// run-time disambiguate potentially overlapping arrays.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/LoopDistribute.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/EquivalenceClasses.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/LoopAccessAnalysis.h"
#include "llvm/Analysis/LoopAnalysisManager.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/LoopVersioning.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <cassert>
#include <functional>
#include <list>
#include <tuple>
#include <utility>
using namespace llvm;
#define LDIST_NAME "loop-distribute"
#define DEBUG_TYPE LDIST_NAME
/// @{
/// Metadata attribute names
static const char *const LLVMLoopDistributeFollowupAll =
"llvm.loop.distribute.followup_all";
static const char *const LLVMLoopDistributeFollowupCoincident =
"llvm.loop.distribute.followup_coincident";
static const char *const LLVMLoopDistributeFollowupSequential =
"llvm.loop.distribute.followup_sequential";
static const char *const LLVMLoopDistributeFollowupFallback =
"llvm.loop.distribute.followup_fallback";
/// @}
static cl::opt<bool>
LDistVerify("loop-distribute-verify", cl::Hidden,
cl::desc("Turn on DominatorTree and LoopInfo verification "
"after Loop Distribution"),
cl::init(false));
static cl::opt<bool> DistributeNonIfConvertible(
"loop-distribute-non-if-convertible", cl::Hidden,
cl::desc("Whether to distribute into a loop that may not be "
"if-convertible by the loop vectorizer"),
cl::init(false));
static cl::opt<unsigned> DistributeSCEVCheckThreshold(
"loop-distribute-scev-check-threshold", cl::init(8), cl::Hidden,
cl::desc("The maximum number of SCEV checks allowed for Loop "
"Distribution"));
static cl::opt<unsigned> PragmaDistributeSCEVCheckThreshold(
"loop-distribute-scev-check-threshold-with-pragma", cl::init(128),
cl::Hidden,
cl::desc(
"The maximum number of SCEV checks allowed for Loop "
"Distribution for loop marked with #pragma loop distribute(enable)"));
static cl::opt<bool> EnableLoopDistribute(
"enable-loop-distribute", cl::Hidden,
cl::desc("Enable the new, experimental LoopDistribution Pass"),
cl::init(false));
STATISTIC(NumLoopsDistributed, "Number of loops distributed");
namespace {
/// Maintains the set of instructions of the loop for a partition before
/// cloning. After cloning, it hosts the new loop.
class InstPartition {
using InstructionSet = SmallPtrSet<Instruction *, 8>;
public:
InstPartition(Instruction *I, Loop *L, bool DepCycle = false)
: DepCycle(DepCycle), OrigLoop(L) {
Set.insert(I);
}
/// Returns whether this partition contains a dependence cycle.
bool hasDepCycle() const { return DepCycle; }
/// Adds an instruction to this partition.
void add(Instruction *I) { Set.insert(I); }
/// Collection accessors.
InstructionSet::iterator begin() { return Set.begin(); }
InstructionSet::iterator end() { return Set.end(); }
InstructionSet::const_iterator begin() const { return Set.begin(); }
InstructionSet::const_iterator end() const { return Set.end(); }
bool empty() const { return Set.empty(); }
/// Moves this partition into \p Other. This partition becomes empty
/// after this.
void moveTo(InstPartition &Other) {
Other.Set.insert(Set.begin(), Set.end());
Set.clear();
Other.DepCycle |= DepCycle;
}
/// Populates the partition with a transitive closure of all the
/// instructions that the seeded instructions dependent on.
void populateUsedSet() {
// FIXME: We currently don't use control-dependence but simply include all
// blocks (possibly empty at the end) and let simplifycfg mostly clean this
// up.
for (auto *B : OrigLoop->getBlocks())
Set.insert(B->getTerminator());
// Follow the use-def chains to form a transitive closure of all the
// instructions that the originally seeded instructions depend on.
SmallVector<Instruction *, 8> Worklist(Set.begin(), Set.end());
while (!Worklist.empty()) {
Instruction *I = Worklist.pop_back_val();
// Insert instructions from the loop that we depend on.
for (Value *V : I->operand_values()) {
auto *I = dyn_cast<Instruction>(V);
if (I && OrigLoop->contains(I->getParent()) && Set.insert(I).second)
Worklist.push_back(I);
}
}
}
/// Clones the original loop.
///
/// Updates LoopInfo and DominatorTree using the information that block \p
/// LoopDomBB dominates the loop.
Loop *cloneLoopWithPreheader(BasicBlock *InsertBefore, BasicBlock *LoopDomBB,
unsigned Index, LoopInfo *LI,
DominatorTree *DT) {
ClonedLoop = ::cloneLoopWithPreheader(InsertBefore, LoopDomBB, OrigLoop,
VMap, Twine(".ldist") + Twine(Index),
LI, DT, ClonedLoopBlocks);
return ClonedLoop;
}
/// The cloned loop. If this partition is mapped to the original loop,
/// this is null.
const Loop *getClonedLoop() const { return ClonedLoop; }
/// Returns the loop where this partition ends up after distribution.
/// If this partition is mapped to the original loop then use the block from
/// the loop.
Loop *getDistributedLoop() const {
return ClonedLoop ? ClonedLoop : OrigLoop;
}
/// The VMap that is populated by cloning and then used in
/// remapinstruction to remap the cloned instructions.
ValueToValueMapTy &getVMap() { return VMap; }
/// Remaps the cloned instructions using VMap.
void remapInstructions() {
remapInstructionsInBlocks(ClonedLoopBlocks, VMap);
}
/// Based on the set of instructions selected for this partition,
/// removes the unnecessary ones.
void removeUnusedInsts() {
SmallVector<Instruction *, 8> Unused;
for (auto *Block : OrigLoop->getBlocks())
for (auto &Inst : *Block)
if (!Set.count(&Inst)) {
Instruction *NewInst = &Inst;
if (!VMap.empty())
NewInst = cast<Instruction>(VMap[NewInst]);
assert(!isa<BranchInst>(NewInst) &&
"Branches are marked used early on");
Unused.push_back(NewInst);
}
// Delete the instructions backwards, as it has a reduced likelihood of
// having to update as many def-use and use-def chains.
for (auto *Inst : reverse(Unused)) {
if (!Inst->use_empty())
Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
Inst->eraseFromParent();
}
}
void print() const {
if (DepCycle)
dbgs() << " (cycle)\n";
for (auto *I : Set)
// Prefix with the block name.
dbgs() << " " << I->getParent()->getName() << ":" << *I << "\n";
}
void printBlocks() const {
for (auto *BB : getDistributedLoop()->getBlocks())
dbgs() << *BB;
}
private:
/// Instructions from OrigLoop selected for this partition.
InstructionSet Set;
/// Whether this partition contains a dependence cycle.
bool DepCycle;
/// The original loop.
Loop *OrigLoop;
/// The cloned loop. If this partition is mapped to the original loop,
/// this is null.
Loop *ClonedLoop = nullptr;
/// The blocks of ClonedLoop including the preheader. If this
/// partition is mapped to the original loop, this is empty.
SmallVector<BasicBlock *, 8> ClonedLoopBlocks;
/// These gets populated once the set of instructions have been
/// finalized. If this partition is mapped to the original loop, these are not
/// set.
ValueToValueMapTy VMap;
};
/// Holds the set of Partitions. It populates them, merges them and then
/// clones the loops.
class InstPartitionContainer {
using InstToPartitionIdT = DenseMap<Instruction *, int>;
public:
InstPartitionContainer(Loop *L, LoopInfo *LI, DominatorTree *DT)
: L(L), LI(LI), DT(DT) {}
/// Returns the number of partitions.
unsigned getSize() const { return PartitionContainer.size(); }
/// Adds \p Inst into the current partition if that is marked to
/// contain cycles. Otherwise start a new partition for it.
void addToCyclicPartition(Instruction *Inst) {
// If the current partition is non-cyclic. Start a new one.
if (PartitionContainer.empty() || !PartitionContainer.back().hasDepCycle())
PartitionContainer.emplace_back(Inst, L, /*DepCycle=*/true);
else
PartitionContainer.back().add(Inst);
}
/// Adds \p Inst into a partition that is not marked to contain
/// dependence cycles.
///
// Initially we isolate memory instructions into as many partitions as
// possible, then later we may merge them back together.
void addToNewNonCyclicPartition(Instruction *Inst) {
PartitionContainer.emplace_back(Inst, L);
}
/// Merges adjacent non-cyclic partitions.
///
/// The idea is that we currently only want to isolate the non-vectorizable
/// partition. We could later allow more distribution among these partition
/// too.
void mergeAdjacentNonCyclic() {
mergeAdjacentPartitionsIf(
[](const InstPartition *P) { return !P->hasDepCycle(); });
}
/// If a partition contains only conditional stores, we won't vectorize
/// it. Try to merge it with a previous cyclic partition.
void mergeNonIfConvertible() {
mergeAdjacentPartitionsIf([&](const InstPartition *Partition) {
if (Partition->hasDepCycle())
return true;
// Now, check if all stores are conditional in this partition.
bool seenStore = false;
for (auto *Inst : *Partition)
if (isa<StoreInst>(Inst)) {
seenStore = true;
if (!LoopAccessInfo::blockNeedsPredication(Inst->getParent(), L, DT))
return false;
}
return seenStore;
});
}
/// Merges the partitions according to various heuristics.
void mergeBeforePopulating() {
mergeAdjacentNonCyclic();
if (!DistributeNonIfConvertible)
mergeNonIfConvertible();
}
/// Merges partitions in order to ensure that no loads are duplicated.
///
/// We can't duplicate loads because that could potentially reorder them.
/// LoopAccessAnalysis provides dependency information with the context that
/// the order of memory operation is preserved.
///
/// Return if any partitions were merged.
bool mergeToAvoidDuplicatedLoads() {
using LoadToPartitionT = DenseMap<Instruction *, InstPartition *>;
using ToBeMergedT = EquivalenceClasses<InstPartition *>;
LoadToPartitionT LoadToPartition;
ToBeMergedT ToBeMerged;
// Step through the partitions and create equivalence between partitions
// that contain the same load. Also put partitions in between them in the
// same equivalence class to avoid reordering of memory operations.
for (PartitionContainerT::iterator I = PartitionContainer.begin(),
E = PartitionContainer.end();
I != E; ++I) {
auto *PartI = &*I;
// If a load occurs in two partitions PartI and PartJ, merge all
// partitions (PartI, PartJ] into PartI.
for (Instruction *Inst : *PartI)
if (isa<LoadInst>(Inst)) {
bool NewElt;
LoadToPartitionT::iterator LoadToPart;
std::tie(LoadToPart, NewElt) =
LoadToPartition.insert(std::make_pair(Inst, PartI));
if (!NewElt) {
LLVM_DEBUG(dbgs()
<< "Merging partitions due to this load in multiple "
<< "partitions: " << PartI << ", " << LoadToPart->second
<< "\n"
<< *Inst << "\n");
auto PartJ = I;
do {
--PartJ;
ToBeMerged.unionSets(PartI, &*PartJ);
} while (&*PartJ != LoadToPart->second);
}
}
}
if (ToBeMerged.empty())
return false;
// Merge the member of an equivalence class into its class leader. This
// makes the members empty.
for (ToBeMergedT::iterator I = ToBeMerged.begin(), E = ToBeMerged.end();
I != E; ++I) {
if (!I->isLeader())
continue;
auto PartI = I->getData();
for (auto PartJ : make_range(std::next(ToBeMerged.member_begin(I)),
ToBeMerged.member_end())) {
PartJ->moveTo(*PartI);
}
}
// Remove the empty partitions.
PartitionContainer.remove_if(
[](const InstPartition &P) { return P.empty(); });
return true;
}
/// Sets up the mapping between instructions to partitions. If the
/// instruction is duplicated across multiple partitions, set the entry to -1.
void setupPartitionIdOnInstructions() {
int PartitionID = 0;
for (const auto &Partition : PartitionContainer) {
for (Instruction *Inst : Partition) {
bool NewElt;
InstToPartitionIdT::iterator Iter;
std::tie(Iter, NewElt) =
InstToPartitionId.insert(std::make_pair(Inst, PartitionID));
if (!NewElt)
Iter->second = -1;
}
++PartitionID;
}
}
/// Populates the partition with everything that the seeding
/// instructions require.
void populateUsedSet() {
for (auto &P : PartitionContainer)
P.populateUsedSet();
}
/// This performs the main chunk of the work of cloning the loops for
/// the partitions.
void cloneLoops() {
BasicBlock *OrigPH = L->getLoopPreheader();
// At this point the predecessor of the preheader is either the memcheck
// block or the top part of the original preheader.
BasicBlock *Pred = OrigPH->getSinglePredecessor();
assert(Pred && "Preheader does not have a single predecessor");
BasicBlock *ExitBlock = L->getExitBlock();
assert(ExitBlock && "No single exit block");
Loop *NewLoop;
assert(!PartitionContainer.empty() && "at least two partitions expected");
// We're cloning the preheader along with the loop so we already made sure
// it was empty.
assert(&*OrigPH->begin() == OrigPH->getTerminator() &&
"preheader not empty");
// Preserve the original loop ID for use after the transformation.
MDNode *OrigLoopID = L->getLoopID();
// Create a loop for each partition except the last. Clone the original
// loop before PH along with adding a preheader for the cloned loop. Then
// update PH to point to the newly added preheader.
BasicBlock *TopPH = OrigPH;
unsigned Index = getSize() - 1;
for (auto I = std::next(PartitionContainer.rbegin()),
E = PartitionContainer.rend();
I != E; ++I, --Index, TopPH = NewLoop->getLoopPreheader()) {
auto *Part = &*I;
NewLoop = Part->cloneLoopWithPreheader(TopPH, Pred, Index, LI, DT);
Part->getVMap()[ExitBlock] = TopPH;
Part->remapInstructions();
setNewLoopID(OrigLoopID, Part);
}
Pred->getTerminator()->replaceUsesOfWith(OrigPH, TopPH);
// Also set a new loop ID for the last loop.
setNewLoopID(OrigLoopID, &PartitionContainer.back());
// Now go in forward order and update the immediate dominator for the
// preheaders with the exiting block of the previous loop. Dominance
// within the loop is updated in cloneLoopWithPreheader.
for (auto Curr = PartitionContainer.cbegin(),
Next = std::next(PartitionContainer.cbegin()),
E = PartitionContainer.cend();
Next != E; ++Curr, ++Next)
DT->changeImmediateDominator(
Next->getDistributedLoop()->getLoopPreheader(),
Curr->getDistributedLoop()->getExitingBlock());
}
/// Removes the dead instructions from the cloned loops.
void removeUnusedInsts() {
for (auto &Partition : PartitionContainer)
Partition.removeUnusedInsts();
}
/// For each memory pointer, it computes the partitionId the pointer is
/// used in.
///
/// This returns an array of int where the I-th entry corresponds to I-th
/// entry in LAI.getRuntimePointerCheck(). If the pointer is used in multiple
/// partitions its entry is set to -1.
SmallVector<int, 8>
computePartitionSetForPointers(const LoopAccessInfo &LAI) {
const RuntimePointerChecking *RtPtrCheck = LAI.getRuntimePointerChecking();
unsigned N = RtPtrCheck->Pointers.size();
SmallVector<int, 8> PtrToPartitions(N);
for (unsigned I = 0; I < N; ++I) {
Value *Ptr = RtPtrCheck->Pointers[I].PointerValue;
auto Instructions =
LAI.getInstructionsForAccess(Ptr, RtPtrCheck->Pointers[I].IsWritePtr);
int &Partition = PtrToPartitions[I];
// First set it to uninitialized.
Partition = -2;
for (Instruction *Inst : Instructions) {
// Note that this could be -1 if Inst is duplicated across multiple
// partitions.
int ThisPartition = this->InstToPartitionId[Inst];
if (Partition == -2)
Partition = ThisPartition;
// -1 means belonging to multiple partitions.
else if (Partition == -1)
break;
else if (Partition != (int)ThisPartition)
Partition = -1;
}
assert(Partition != -2 && "Pointer not belonging to any partition");
}
return PtrToPartitions;
}
void print(raw_ostream &OS) const {
unsigned Index = 0;
for (const auto &P : PartitionContainer) {
OS << "Partition " << Index++ << " (" << &P << "):\n";
P.print();
}
}
void dump() const { print(dbgs()); }
#ifndef NDEBUG
friend raw_ostream &operator<<(raw_ostream &OS,
const InstPartitionContainer &Partitions) {
Partitions.print(OS);
return OS;
}
#endif
void printBlocks() const {
unsigned Index = 0;
for (const auto &P : PartitionContainer) {
dbgs() << "\nPartition " << Index++ << " (" << &P << "):\n";
P.printBlocks();
}
}
private:
using PartitionContainerT = std::list<InstPartition>;
/// List of partitions.
PartitionContainerT PartitionContainer;
/// Mapping from Instruction to partition Id. If the instruction
/// belongs to multiple partitions the entry contains -1.
InstToPartitionIdT InstToPartitionId;
Loop *L;
LoopInfo *LI;
DominatorTree *DT;
/// The control structure to merge adjacent partitions if both satisfy
/// the \p Predicate.
template <class UnaryPredicate>
void mergeAdjacentPartitionsIf(UnaryPredicate Predicate) {
InstPartition *PrevMatch = nullptr;
for (auto I = PartitionContainer.begin(); I != PartitionContainer.end();) {
auto DoesMatch = Predicate(&*I);
if (PrevMatch == nullptr && DoesMatch) {
PrevMatch = &*I;
++I;
} else if (PrevMatch != nullptr && DoesMatch) {
I->moveTo(*PrevMatch);
I = PartitionContainer.erase(I);
} else {
PrevMatch = nullptr;
++I;
}
}
}
/// Assign new LoopIDs for the partition's cloned loop.
void setNewLoopID(MDNode *OrigLoopID, InstPartition *Part) {
Optional<MDNode *> PartitionID = makeFollowupLoopID(
OrigLoopID,
{LLVMLoopDistributeFollowupAll,
Part->hasDepCycle() ? LLVMLoopDistributeFollowupSequential
: LLVMLoopDistributeFollowupCoincident});
if (PartitionID.hasValue()) {
Loop *NewLoop = Part->getDistributedLoop();
NewLoop->setLoopID(PartitionID.getValue());
}
}
};
/// For each memory instruction, this class maintains difference of the
/// number of unsafe dependences that start out from this instruction minus
/// those that end here.
///
/// By traversing the memory instructions in program order and accumulating this
/// number, we know whether any unsafe dependence crosses over a program point.
class MemoryInstructionDependences {
using Dependence = MemoryDepChecker::Dependence;
public:
struct Entry {
Instruction *Inst;
unsigned NumUnsafeDependencesStartOrEnd = 0;
Entry(Instruction *Inst) : Inst(Inst) {}
};
using AccessesType = SmallVector<Entry, 8>;
AccessesType::const_iterator begin() const { return Accesses.begin(); }
AccessesType::const_iterator end() const { return Accesses.end(); }
MemoryInstructionDependences(
const SmallVectorImpl<Instruction *> &Instructions,
const SmallVectorImpl<Dependence> &Dependences) {
Accesses.append(Instructions.begin(), Instructions.end());
LLVM_DEBUG(dbgs() << "Backward dependences:\n");
for (auto &Dep : Dependences)
if (Dep.isPossiblyBackward()) {
// Note that the designations source and destination follow the program
// order, i.e. source is always first. (The direction is given by the
// DepType.)
++Accesses[Dep.Source].NumUnsafeDependencesStartOrEnd;
--Accesses[Dep.Destination].NumUnsafeDependencesStartOrEnd;
LLVM_DEBUG(Dep.print(dbgs(), 2, Instructions));
}
}
private:
AccessesType Accesses;
};
/// The actual class performing the per-loop work.
class LoopDistributeForLoop {
public:
LoopDistributeForLoop(Loop *L, Function *F, LoopInfo *LI, DominatorTree *DT,
ScalarEvolution *SE, OptimizationRemarkEmitter *ORE)
: L(L), F(F), LI(LI), DT(DT), SE(SE), ORE(ORE) {
setForced();
}
/// Try to distribute an inner-most loop.
bool processLoop(std::function<const LoopAccessInfo &(Loop &)> &GetLAA) {
assert(L->isInnermost() && "Only process inner loops.");
LLVM_DEBUG(dbgs() << "\nLDist: In \""
<< L->getHeader()->getParent()->getName()
<< "\" checking " << *L << "\n");
if (!L->getExitBlock())
return fail("MultipleExitBlocks", "multiple exit blocks");
if (!L->isLoopSimplifyForm())
return fail("NotLoopSimplifyForm",
"loop is not in loop-simplify form");
BasicBlock *PH = L->getLoopPreheader();
// LAA will check that we only have a single exiting block.
LAI = &GetLAA(*L);
// Currently, we only distribute to isolate the part of the loop with
// dependence cycles to enable partial vectorization.
if (LAI->canVectorizeMemory())
return fail("MemOpsCanBeVectorized",
"memory operations are safe for vectorization");
auto *Dependences = LAI->getDepChecker().getDependences();
if (!Dependences || Dependences->empty())
return fail("NoUnsafeDeps", "no unsafe dependences to isolate");
InstPartitionContainer Partitions(L, LI, DT);
// First, go through each memory operation and assign them to consecutive
// partitions (the order of partitions follows program order). Put those
// with unsafe dependences into "cyclic" partition otherwise put each store
// in its own "non-cyclic" partition (we'll merge these later).
//
// Note that a memory operation (e.g. Load2 below) at a program point that
// has an unsafe dependence (Store3->Load1) spanning over it must be
// included in the same cyclic partition as the dependent operations. This
// is to preserve the original program order after distribution. E.g.:
//
// NumUnsafeDependencesStartOrEnd NumUnsafeDependencesActive
// Load1 -. 1 0->1
// Load2 | /Unsafe/ 0 1
// Store3 -' -1 1->0
// Load4 0 0
//
// NumUnsafeDependencesActive > 0 indicates this situation and in this case
// we just keep assigning to the same cyclic partition until
// NumUnsafeDependencesActive reaches 0.
const MemoryDepChecker &DepChecker = LAI->getDepChecker();
MemoryInstructionDependences MID(DepChecker.getMemoryInstructions(),
*Dependences);
int NumUnsafeDependencesActive = 0;
for (auto &InstDep : MID) {
Instruction *I = InstDep.Inst;
// We update NumUnsafeDependencesActive post-instruction, catch the
// start of a dependence directly via NumUnsafeDependencesStartOrEnd.
if (NumUnsafeDependencesActive ||
InstDep.NumUnsafeDependencesStartOrEnd > 0)
Partitions.addToCyclicPartition(I);
else
Partitions.addToNewNonCyclicPartition(I);
NumUnsafeDependencesActive += InstDep.NumUnsafeDependencesStartOrEnd;
assert(NumUnsafeDependencesActive >= 0 &&
"Negative number of dependences active");
}
// Add partitions for values used outside. These partitions can be out of
// order from the original program order. This is OK because if the
// partition uses a load we will merge this partition with the original
// partition of the load that we set up in the previous loop (see
// mergeToAvoidDuplicatedLoads).
auto DefsUsedOutside = findDefsUsedOutsideOfLoop(L);
for (auto *Inst : DefsUsedOutside)
Partitions.addToNewNonCyclicPartition(Inst);
LLVM_DEBUG(dbgs() << "Seeded partitions:\n" << Partitions);
if (Partitions.getSize() < 2)
return fail("CantIsolateUnsafeDeps",
"cannot isolate unsafe dependencies");
// Run the merge heuristics: Merge non-cyclic adjacent partitions since we
// should be able to vectorize these together.
Partitions.mergeBeforePopulating();
LLVM_DEBUG(dbgs() << "\nMerged partitions:\n" << Partitions);
if (Partitions.getSize() < 2)
return fail("CantIsolateUnsafeDeps",
"cannot isolate unsafe dependencies");
// Now, populate the partitions with non-memory operations.
Partitions.populateUsedSet();
LLVM_DEBUG(dbgs() << "\nPopulated partitions:\n" << Partitions);
// In order to preserve original lexical order for loads, keep them in the
// partition that we set up in the MemoryInstructionDependences loop.
if (Partitions.mergeToAvoidDuplicatedLoads()) {
LLVM_DEBUG(dbgs() << "\nPartitions merged to ensure unique loads:\n"
<< Partitions);
if (Partitions.getSize() < 2)
return fail("CantIsolateUnsafeDeps",
"cannot isolate unsafe dependencies");
}
// Don't distribute the loop if we need too many SCEV run-time checks, or
// any if it's illegal.
const SCEVUnionPredicate &Pred = LAI->getPSE().getUnionPredicate();
if (LAI->hasConvergentOp() && !Pred.isAlwaysTrue()) {
return fail("RuntimeCheckWithConvergent",
"may not insert runtime check with convergent operation");
}
if (Pred.getComplexity() > (IsForced.getValueOr(false)
? PragmaDistributeSCEVCheckThreshold
: DistributeSCEVCheckThreshold))
return fail("TooManySCEVRuntimeChecks",
"too many SCEV run-time checks needed.\n");
if (!IsForced.getValueOr(false) && hasDisableAllTransformsHint(L))
return fail("HeuristicDisabled", "distribution heuristic disabled");
LLVM_DEBUG(dbgs() << "\nDistributing loop: " << *L << "\n");
// We're done forming the partitions set up the reverse mapping from
// instructions to partitions.
Partitions.setupPartitionIdOnInstructions();
// If we need run-time checks, version the loop now.
auto PtrToPartition = Partitions.computePartitionSetForPointers(*LAI);
const auto *RtPtrChecking = LAI->getRuntimePointerChecking();
const auto &AllChecks = RtPtrChecking->getChecks();
auto Checks = includeOnlyCrossPartitionChecks(AllChecks, PtrToPartition,
RtPtrChecking);
if (LAI->hasConvergentOp() && !Checks.empty()) {
return fail("RuntimeCheckWithConvergent",
"may not insert runtime check with convergent operation");
}
// To keep things simple have an empty preheader before we version or clone
// the loop. (Also split if this has no predecessor, i.e. entry, because we
// rely on PH having a predecessor.)
if (!PH->getSinglePredecessor() || &*PH->begin() != PH->getTerminator())
SplitBlock(PH, PH->getTerminator(), DT, LI);
if (!Pred.isAlwaysTrue() || !Checks.empty()) {
assert(!LAI->hasConvergentOp() && "inserting illegal loop versioning");
MDNode *OrigLoopID = L->getLoopID();
LLVM_DEBUG(dbgs() << "\nPointers:\n");
LLVM_DEBUG(LAI->getRuntimePointerChecking()->printChecks(dbgs(), Checks));
LoopVersioning LVer(*LAI, Checks, L, LI, DT, SE);
LVer.versionLoop(DefsUsedOutside);
LVer.annotateLoopWithNoAlias();
// The unversioned loop will not be changed, so we inherit all attributes
// from the original loop, but remove the loop distribution metadata to
// avoid to distribute it again.
MDNode *UnversionedLoopID =
makeFollowupLoopID(OrigLoopID,
{LLVMLoopDistributeFollowupAll,
LLVMLoopDistributeFollowupFallback},
"llvm.loop.distribute.", true)
.getValue();
LVer.getNonVersionedLoop()->setLoopID(UnversionedLoopID);
}
// Create identical copies of the original loop for each partition and hook
// them up sequentially.
Partitions.cloneLoops();
// Now, we remove the instruction from each loop that don't belong to that
// partition.
Partitions.removeUnusedInsts();
LLVM_DEBUG(dbgs() << "\nAfter removing unused Instrs:\n");
LLVM_DEBUG(Partitions.printBlocks());
if (LDistVerify) {
LI->verify(*DT);
assert(DT->verify(DominatorTree::VerificationLevel::Fast));
}
++NumLoopsDistributed;
// Report the success.
ORE->emit([&]() {
return OptimizationRemark(LDIST_NAME, "Distribute", L->getStartLoc(),
L->getHeader())
<< "distributed loop";
});
return true;
}
/// Provide diagnostics then \return with false.
bool fail(StringRef RemarkName, StringRef Message) {
LLVMContext &Ctx = F->getContext();
bool Forced = isForced().getValueOr(false);
LLVM_DEBUG(dbgs() << "Skipping; " << Message << "\n");
// With Rpass-missed report that distribution failed.
ORE->emit([&]() {
return OptimizationRemarkMissed(LDIST_NAME, "NotDistributed",
L->getStartLoc(), L->getHeader())
<< "loop not distributed: use -Rpass-analysis=loop-distribute for "
"more "
"info";
});
// With Rpass-analysis report why. This is on by default if distribution
// was requested explicitly.
ORE->emit(OptimizationRemarkAnalysis(
Forced ? OptimizationRemarkAnalysis::AlwaysPrint : LDIST_NAME,
RemarkName, L->getStartLoc(), L->getHeader())
<< "loop not distributed: " << Message);
// Also issue a warning if distribution was requested explicitly but it
// failed.
if (Forced)
Ctx.diagnose(DiagnosticInfoOptimizationFailure(
*F, L->getStartLoc(), "loop not distributed: failed "
"explicitly specified loop distribution"));
return false;
}
/// Return if distribution forced to be enabled/disabled for the loop.
///
/// If the optional has a value, it indicates whether distribution was forced
/// to be enabled (true) or disabled (false). If the optional has no value
/// distribution was not forced either way.
const Optional<bool> &isForced() const { return IsForced; }
private:
/// Filter out checks between pointers from the same partition.
///
/// \p PtrToPartition contains the partition number for pointers. Partition
/// number -1 means that the pointer is used in multiple partitions. In this
/// case we can't safely omit the check.
SmallVector<RuntimePointerCheck, 4> includeOnlyCrossPartitionChecks(
const SmallVectorImpl<RuntimePointerCheck> &AllChecks,
const SmallVectorImpl<int> &PtrToPartition,
const RuntimePointerChecking *RtPtrChecking) {
SmallVector<RuntimePointerCheck, 4> Checks;
copy_if(AllChecks, std::back_inserter(Checks),
[&](const RuntimePointerCheck &Check) {
for (unsigned PtrIdx1 : Check.first->Members)
for (unsigned PtrIdx2 : Check.second->Members)
// Only include this check if there is a pair of pointers
// that require checking and the pointers fall into
// separate partitions.
//
// (Note that we already know at this point that the two
// pointer groups need checking but it doesn't follow
// that each pair of pointers within the two groups need
// checking as well.
//
// In other words we don't want to include a check just
// because there is a pair of pointers between the two
// pointer groups that require checks and a different
// pair whose pointers fall into different partitions.)
if (RtPtrChecking->needsChecking(PtrIdx1, PtrIdx2) &&
!RuntimePointerChecking::arePointersInSamePartition(
PtrToPartition, PtrIdx1, PtrIdx2))
return true;
return false;
});
return Checks;
}
/// Check whether the loop metadata is forcing distribution to be
/// enabled/disabled.
void setForced() {
Optional<const MDOperand *> Value =
findStringMetadataForLoop(L, "llvm.loop.distribute.enable");
if (!Value)
return;
const MDOperand *Op = *Value;
assert(Op && mdconst::hasa<ConstantInt>(*Op) && "invalid metadata");
IsForced = mdconst::extract<ConstantInt>(*Op)->getZExtValue();
}
Loop *L;
Function *F;
// Analyses used.
LoopInfo *LI;
const LoopAccessInfo *LAI = nullptr;
DominatorTree *DT;
ScalarEvolution *SE;
OptimizationRemarkEmitter *ORE;
/// Indicates whether distribution is forced to be enabled/disabled for
/// the loop.
///
/// If the optional has a value, it indicates whether distribution was forced
/// to be enabled (true) or disabled (false). If the optional has no value
/// distribution was not forced either way.
Optional<bool> IsForced;
};
} // end anonymous namespace
/// Shared implementation between new and old PMs.
static bool runImpl(Function &F, LoopInfo *LI, DominatorTree *DT,
ScalarEvolution *SE, OptimizationRemarkEmitter *ORE,
std::function<const LoopAccessInfo &(Loop &)> &GetLAA) {
// Build up a worklist of inner-loops to vectorize. This is necessary as the
// act of distributing a loop creates new loops and can invalidate iterators
// across the loops.
SmallVector<Loop *, 8> Worklist;
for (Loop *TopLevelLoop : *LI)
for (Loop *L : depth_first(TopLevelLoop))
// We only handle inner-most loops.
if (L->isInnermost())
Worklist.push_back(L);
// Now walk the identified inner loops.
bool Changed = false;
for (Loop *L : Worklist) {
LoopDistributeForLoop LDL(L, &F, LI, DT, SE, ORE);
// If distribution was forced for the specific loop to be
// enabled/disabled, follow that. Otherwise use the global flag.
if (LDL.isForced().getValueOr(EnableLoopDistribute))
Changed |= LDL.processLoop(GetLAA);
}
// Process each loop nest in the function.
return Changed;
}
namespace {
/// The pass class.
class LoopDistributeLegacy : public FunctionPass {
public:
static char ID;
LoopDistributeLegacy() : FunctionPass(ID) {
// The default is set by the caller.
initializeLoopDistributeLegacyPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
auto *LAA = &getAnalysis<LoopAccessLegacyAnalysis>();
auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
auto *ORE = &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
std::function<const LoopAccessInfo &(Loop &)> GetLAA =
[&](Loop &L) -> const LoopAccessInfo & { return LAA->getInfo(&L); };
return runImpl(F, LI, DT, SE, ORE, GetLAA);
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.addPreserved<LoopInfoWrapperPass>();
AU.addRequired<LoopAccessLegacyAnalysis>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
}
};
} // end anonymous namespace
PreservedAnalyses LoopDistributePass::run(Function &F,
FunctionAnalysisManager &AM) {
auto &LI = AM.getResult<LoopAnalysis>(F);
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
// We don't directly need these analyses but they're required for loop
// analyses so provide them below.
auto &AA = AM.getResult<AAManager>(F);
auto &AC = AM.getResult<AssumptionAnalysis>(F);
auto &TTI = AM.getResult<TargetIRAnalysis>(F);
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &LAM = AM.getResult<LoopAnalysisManagerFunctionProxy>(F).getManager();
std::function<const LoopAccessInfo &(Loop &)> GetLAA =
[&](Loop &L) -> const LoopAccessInfo & {
LoopStandardAnalysisResults AR = {AA, AC, DT, LI, SE,
TLI, TTI, nullptr, nullptr};
return LAM.getResult<LoopAccessAnalysis>(L, AR);
};
bool Changed = runImpl(F, &LI, &DT, &SE, &ORE, GetLAA);
if (!Changed)
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserve<LoopAnalysis>();
PA.preserve<DominatorTreeAnalysis>();
PA.preserve<GlobalsAA>();
return PA;
}
char LoopDistributeLegacy::ID;
static const char ldist_name[] = "Loop Distribution";
INITIALIZE_PASS_BEGIN(LoopDistributeLegacy, LDIST_NAME, ldist_name, false,
false)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopAccessLegacyAnalysis)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
INITIALIZE_PASS_END(LoopDistributeLegacy, LDIST_NAME, ldist_name, false, false)
FunctionPass *llvm::createLoopDistributePass() { return new LoopDistributeLegacy(); }
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