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llvm-mirror/lib/Analysis/MemorySSAUpdater.cpp
Chandler Carruth ae65e281f3 Update the file headers across all of the LLVM projects in the monorepo 
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636
2019-01-19 08:50:56 +00:00

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//===-- MemorySSAUpdater.cpp - Memory SSA Updater--------------------===//
//
// 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 MemorySSAUpdater class.
//
//===----------------------------------------------------------------===//
#include "llvm/Analysis/MemorySSAUpdater.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/IteratedDominanceFrontier.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/FormattedStream.h"
#include <algorithm>
#define DEBUG_TYPE "memoryssa"
using namespace llvm;
// This is the marker algorithm from "Simple and Efficient Construction of
// Static Single Assignment Form"
// The simple, non-marker algorithm places phi nodes at any join
// Here, we place markers, and only place phi nodes if they end up necessary.
// They are only necessary if they break a cycle (IE we recursively visit
// ourselves again), or we discover, while getting the value of the operands,
// that there are two or more definitions needing to be merged.
// This still will leave non-minimal form in the case of irreducible control
// flow, where phi nodes may be in cycles with themselves, but unnecessary.
MemoryAccess *MemorySSAUpdater::getPreviousDefRecursive(
BasicBlock *BB,
DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &CachedPreviousDef) {
// First, do a cache lookup. Without this cache, certain CFG structures
// (like a series of if statements) take exponential time to visit.
auto Cached = CachedPreviousDef.find(BB);
if (Cached != CachedPreviousDef.end()) {
return Cached->second;
}
if (BasicBlock *Pred = BB->getSinglePredecessor()) {
// Single predecessor case, just recurse, we can only have one definition.
MemoryAccess *Result = getPreviousDefFromEnd(Pred, CachedPreviousDef);
CachedPreviousDef.insert({BB, Result});
return Result;
}
if (VisitedBlocks.count(BB)) {
// We hit our node again, meaning we had a cycle, we must insert a phi
// node to break it so we have an operand. The only case this will
// insert useless phis is if we have irreducible control flow.
MemoryAccess *Result = MSSA->createMemoryPhi(BB);
CachedPreviousDef.insert({BB, Result});
return Result;
}
if (VisitedBlocks.insert(BB).second) {
// Mark us visited so we can detect a cycle
SmallVector<TrackingVH<MemoryAccess>, 8> PhiOps;
// Recurse to get the values in our predecessors for placement of a
// potential phi node. This will insert phi nodes if we cycle in order to
// break the cycle and have an operand.
for (auto *Pred : predecessors(BB))
PhiOps.push_back(getPreviousDefFromEnd(Pred, CachedPreviousDef));
// Now try to simplify the ops to avoid placing a phi.
// This may return null if we never created a phi yet, that's okay
MemoryPhi *Phi = dyn_cast_or_null<MemoryPhi>(MSSA->getMemoryAccess(BB));
// See if we can avoid the phi by simplifying it.
auto *Result = tryRemoveTrivialPhi(Phi, PhiOps);
// If we couldn't simplify, we may have to create a phi
if (Result == Phi) {
if (!Phi)
Phi = MSSA->createMemoryPhi(BB);
// See if the existing phi operands match what we need.
// Unlike normal SSA, we only allow one phi node per block, so we can't just
// create a new one.
if (Phi->getNumOperands() != 0) {
// FIXME: Figure out whether this is dead code and if so remove it.
if (!std::equal(Phi->op_begin(), Phi->op_end(), PhiOps.begin())) {
// These will have been filled in by the recursive read we did above.
llvm::copy(PhiOps, Phi->op_begin());
std::copy(pred_begin(BB), pred_end(BB), Phi->block_begin());
}
} else {
unsigned i = 0;
for (auto *Pred : predecessors(BB))
Phi->addIncoming(&*PhiOps[i++], Pred);
InsertedPHIs.push_back(Phi);
}
Result = Phi;
}
// Set ourselves up for the next variable by resetting visited state.
VisitedBlocks.erase(BB);
CachedPreviousDef.insert({BB, Result});
return Result;
}
llvm_unreachable("Should have hit one of the three cases above");
}
// This starts at the memory access, and goes backwards in the block to find the
// previous definition. If a definition is not found the block of the access,
// it continues globally, creating phi nodes to ensure we have a single
// definition.
MemoryAccess *MemorySSAUpdater::getPreviousDef(MemoryAccess *MA) {
if (auto *LocalResult = getPreviousDefInBlock(MA))
return LocalResult;
DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> CachedPreviousDef;
return getPreviousDefRecursive(MA->getBlock(), CachedPreviousDef);
}
// This starts at the memory access, and goes backwards in the block to the find
// the previous definition. If the definition is not found in the block of the
// access, it returns nullptr.
MemoryAccess *MemorySSAUpdater::getPreviousDefInBlock(MemoryAccess *MA) {
auto *Defs = MSSA->getWritableBlockDefs(MA->getBlock());
// It's possible there are no defs, or we got handed the first def to start.
if (Defs) {
// If this is a def, we can just use the def iterators.
if (!isa<MemoryUse>(MA)) {
auto Iter = MA->getReverseDefsIterator();
++Iter;
if (Iter != Defs->rend())
return &*Iter;
} else {
// Otherwise, have to walk the all access iterator.
auto End = MSSA->getWritableBlockAccesses(MA->getBlock())->rend();
for (auto &U : make_range(++MA->getReverseIterator(), End))
if (!isa<MemoryUse>(U))
return cast<MemoryAccess>(&U);
// Note that if MA comes before Defs->begin(), we won't hit a def.
return nullptr;
}
}
return nullptr;
}
// This starts at the end of block
MemoryAccess *MemorySSAUpdater::getPreviousDefFromEnd(
BasicBlock *BB,
DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &CachedPreviousDef) {
auto *Defs = MSSA->getWritableBlockDefs(BB);
if (Defs)
return &*Defs->rbegin();
return getPreviousDefRecursive(BB, CachedPreviousDef);
}
// Recurse over a set of phi uses to eliminate the trivial ones
MemoryAccess *MemorySSAUpdater::recursePhi(MemoryAccess *Phi) {
if (!Phi)
return nullptr;
TrackingVH<MemoryAccess> Res(Phi);
SmallVector<TrackingVH<Value>, 8> Uses;
std::copy(Phi->user_begin(), Phi->user_end(), std::back_inserter(Uses));
for (auto &U : Uses) {
if (MemoryPhi *UsePhi = dyn_cast<MemoryPhi>(&*U)) {
auto OperRange = UsePhi->operands();
tryRemoveTrivialPhi(UsePhi, OperRange);
}
}
return Res;
}
// Eliminate trivial phis
// Phis are trivial if they are defined either by themselves, or all the same
// argument.
// IE phi(a, a) or b = phi(a, b) or c = phi(a, a, c)
// We recursively try to remove them.
template <class RangeType>
MemoryAccess *MemorySSAUpdater::tryRemoveTrivialPhi(MemoryPhi *Phi,
RangeType &Operands) {
// Bail out on non-opt Phis.
if (NonOptPhis.count(Phi))
return Phi;
// Detect equal or self arguments
MemoryAccess *Same = nullptr;
for (auto &Op : Operands) {
// If the same or self, good so far
if (Op == Phi || Op == Same)
continue;
// not the same, return the phi since it's not eliminatable by us
if (Same)
return Phi;
Same = cast<MemoryAccess>(&*Op);
}
// Never found a non-self reference, the phi is undef
if (Same == nullptr)
return MSSA->getLiveOnEntryDef();
if (Phi) {
Phi->replaceAllUsesWith(Same);
removeMemoryAccess(Phi);
}
// We should only end up recursing in case we replaced something, in which
// case, we may have made other Phis trivial.
return recursePhi(Same);
}
void MemorySSAUpdater::insertUse(MemoryUse *MU) {
InsertedPHIs.clear();
MU->setDefiningAccess(getPreviousDef(MU));
// Unlike for defs, there is no extra work to do. Because uses do not create
// new may-defs, there are only two cases:
//
// 1. There was a def already below us, and therefore, we should not have
// created a phi node because it was already needed for the def.
//
// 2. There is no def below us, and therefore, there is no extra renaming work
// to do.
}
// Set every incoming edge {BB, MP->getBlock()} of MemoryPhi MP to NewDef.
static void setMemoryPhiValueForBlock(MemoryPhi *MP, const BasicBlock *BB,
MemoryAccess *NewDef) {
// Replace any operand with us an incoming block with the new defining
// access.
int i = MP->getBasicBlockIndex(BB);
assert(i != -1 && "Should have found the basic block in the phi");
// We can't just compare i against getNumOperands since one is signed and the
// other not. So use it to index into the block iterator.
for (auto BBIter = MP->block_begin() + i; BBIter != MP->block_end();
++BBIter) {
if (*BBIter != BB)
break;
MP->setIncomingValue(i, NewDef);
++i;
}
}
// A brief description of the algorithm:
// First, we compute what should define the new def, using the SSA
// construction algorithm.
// Then, we update the defs below us (and any new phi nodes) in the graph to
// point to the correct new defs, to ensure we only have one variable, and no
// disconnected stores.
void MemorySSAUpdater::insertDef(MemoryDef *MD, bool RenameUses) {
InsertedPHIs.clear();
// See if we had a local def, and if not, go hunting.
MemoryAccess *DefBefore = getPreviousDef(MD);
bool DefBeforeSameBlock = DefBefore->getBlock() == MD->getBlock();
// There is a def before us, which means we can replace any store/phi uses
// of that thing with us, since we are in the way of whatever was there
// before.
// We now define that def's memorydefs and memoryphis
if (DefBeforeSameBlock) {
for (auto UI = DefBefore->use_begin(), UE = DefBefore->use_end();
UI != UE;) {
Use &U = *UI++;
// Leave the MemoryUses alone.
// Also make sure we skip ourselves to avoid self references.
if (isa<MemoryUse>(U.getUser()) || U.getUser() == MD)
continue;
U.set(MD);
}
}
// and that def is now our defining access.
MD->setDefiningAccess(DefBefore);
SmallVector<WeakVH, 8> FixupList(InsertedPHIs.begin(), InsertedPHIs.end());
if (!DefBeforeSameBlock) {
// If there was a local def before us, we must have the same effect it
// did. Because every may-def is the same, any phis/etc we would create, it
// would also have created. If there was no local def before us, we
// performed a global update, and have to search all successors and make
// sure we update the first def in each of them (following all paths until
// we hit the first def along each path). This may also insert phi nodes.
// TODO: There are other cases we can skip this work, such as when we have a
// single successor, and only used a straight line of single pred blocks
// backwards to find the def. To make that work, we'd have to track whether
// getDefRecursive only ever used the single predecessor case. These types
// of paths also only exist in between CFG simplifications.
FixupList.push_back(MD);
}
while (!FixupList.empty()) {
unsigned StartingPHISize = InsertedPHIs.size();
fixupDefs(FixupList);
FixupList.clear();
// Put any new phis on the fixup list, and process them
FixupList.append(InsertedPHIs.begin() + StartingPHISize, InsertedPHIs.end());
}
// Now that all fixups are done, rename all uses if we are asked.
if (RenameUses) {
SmallPtrSet<BasicBlock *, 16> Visited;
BasicBlock *StartBlock = MD->getBlock();
// We are guaranteed there is a def in the block, because we just got it
// handed to us in this function.
MemoryAccess *FirstDef = &*MSSA->getWritableBlockDefs(StartBlock)->begin();
// Convert to incoming value if it's a memorydef. A phi *is* already an
// incoming value.
if (auto *MD = dyn_cast<MemoryDef>(FirstDef))
FirstDef = MD->getDefiningAccess();
MSSA->renamePass(MD->getBlock(), FirstDef, Visited);
// We just inserted a phi into this block, so the incoming value will become
// the phi anyway, so it does not matter what we pass.
for (auto &MP : InsertedPHIs) {
MemoryPhi *Phi = dyn_cast_or_null<MemoryPhi>(MP);
if (Phi)
MSSA->renamePass(Phi->getBlock(), nullptr, Visited);
}
}
}
void MemorySSAUpdater::fixupDefs(const SmallVectorImpl<WeakVH> &Vars) {
SmallPtrSet<const BasicBlock *, 8> Seen;
SmallVector<const BasicBlock *, 16> Worklist;
for (auto &Var : Vars) {
MemoryAccess *NewDef = dyn_cast_or_null<MemoryAccess>(Var);
if (!NewDef)
continue;
// First, see if there is a local def after the operand.
auto *Defs = MSSA->getWritableBlockDefs(NewDef->getBlock());
auto DefIter = NewDef->getDefsIterator();
// The temporary Phi is being fixed, unmark it for not to optimize.
if (MemoryPhi *Phi = dyn_cast<MemoryPhi>(NewDef))
NonOptPhis.erase(Phi);
// If there is a local def after us, we only have to rename that.
if (++DefIter != Defs->end()) {
cast<MemoryDef>(DefIter)->setDefiningAccess(NewDef);
continue;
}
// Otherwise, we need to search down through the CFG.
// For each of our successors, handle it directly if their is a phi, or
// place on the fixup worklist.
for (const auto *S : successors(NewDef->getBlock())) {
if (auto *MP = MSSA->getMemoryAccess(S))
setMemoryPhiValueForBlock(MP, NewDef->getBlock(), NewDef);
else
Worklist.push_back(S);
}
while (!Worklist.empty()) {
const BasicBlock *FixupBlock = Worklist.back();
Worklist.pop_back();
// Get the first def in the block that isn't a phi node.
if (auto *Defs = MSSA->getWritableBlockDefs(FixupBlock)) {
auto *FirstDef = &*Defs->begin();
// The loop above and below should have taken care of phi nodes
assert(!isa<MemoryPhi>(FirstDef) &&
"Should have already handled phi nodes!");
// We are now this def's defining access, make sure we actually dominate
// it
assert(MSSA->dominates(NewDef, FirstDef) &&
"Should have dominated the new access");
// This may insert new phi nodes, because we are not guaranteed the
// block we are processing has a single pred, and depending where the
// store was inserted, it may require phi nodes below it.
cast<MemoryDef>(FirstDef)->setDefiningAccess(getPreviousDef(FirstDef));
return;
}
// We didn't find a def, so we must continue.
for (const auto *S : successors(FixupBlock)) {
// If there is a phi node, handle it.
// Otherwise, put the block on the worklist
if (auto *MP = MSSA->getMemoryAccess(S))
setMemoryPhiValueForBlock(MP, FixupBlock, NewDef);
else {
// If we cycle, we should have ended up at a phi node that we already
// processed. FIXME: Double check this
if (!Seen.insert(S).second)
continue;
Worklist.push_back(S);
}
}
}
}
}
void MemorySSAUpdater::removeEdge(BasicBlock *From, BasicBlock *To) {
if (MemoryPhi *MPhi = MSSA->getMemoryAccess(To)) {
MPhi->unorderedDeleteIncomingBlock(From);
if (MPhi->getNumIncomingValues() == 1)
removeMemoryAccess(MPhi);
}
}
void MemorySSAUpdater::removeDuplicatePhiEdgesBetween(BasicBlock *From,
BasicBlock *To) {
if (MemoryPhi *MPhi = MSSA->getMemoryAccess(To)) {
bool Found = false;
MPhi->unorderedDeleteIncomingIf([&](const MemoryAccess *, BasicBlock *B) {
if (From != B)
return false;
if (Found)
return true;
Found = true;
return false;
});
if (MPhi->getNumIncomingValues() == 1)
removeMemoryAccess(MPhi);
}
}
void MemorySSAUpdater::cloneUsesAndDefs(BasicBlock *BB, BasicBlock *NewBB,
const ValueToValueMapTy &VMap,
PhiToDefMap &MPhiMap) {
auto GetNewDefiningAccess = [&](MemoryAccess *MA) -> MemoryAccess * {
MemoryAccess *InsnDefining = MA;
if (MemoryUseOrDef *DefMUD = dyn_cast<MemoryUseOrDef>(InsnDefining)) {
if (!MSSA->isLiveOnEntryDef(DefMUD)) {
Instruction *DefMUDI = DefMUD->getMemoryInst();
assert(DefMUDI && "Found MemoryUseOrDef with no Instruction.");
if (Instruction *NewDefMUDI =
cast_or_null<Instruction>(VMap.lookup(DefMUDI)))
InsnDefining = MSSA->getMemoryAccess(NewDefMUDI);
}
} else {
MemoryPhi *DefPhi = cast<MemoryPhi>(InsnDefining);
if (MemoryAccess *NewDefPhi = MPhiMap.lookup(DefPhi))
InsnDefining = NewDefPhi;
}
assert(InsnDefining && "Defining instruction cannot be nullptr.");
return InsnDefining;
};
const MemorySSA::AccessList *Acc = MSSA->getBlockAccesses(BB);
if (!Acc)
return;
for (const MemoryAccess &MA : *Acc) {
if (const MemoryUseOrDef *MUD = dyn_cast<MemoryUseOrDef>(&MA)) {
Instruction *Insn = MUD->getMemoryInst();
// Entry does not exist if the clone of the block did not clone all
// instructions. This occurs in LoopRotate when cloning instructions
// from the old header to the old preheader. The cloned instruction may
// also be a simplified Value, not an Instruction (see LoopRotate).
if (Instruction *NewInsn =
dyn_cast_or_null<Instruction>(VMap.lookup(Insn))) {
MemoryAccess *NewUseOrDef = MSSA->createDefinedAccess(
NewInsn, GetNewDefiningAccess(MUD->getDefiningAccess()), MUD);
MSSA->insertIntoListsForBlock(NewUseOrDef, NewBB, MemorySSA::End);
}
}
}
}
void MemorySSAUpdater::updateForClonedLoop(const LoopBlocksRPO &LoopBlocks,
ArrayRef<BasicBlock *> ExitBlocks,
const ValueToValueMapTy &VMap,
bool IgnoreIncomingWithNoClones) {
PhiToDefMap MPhiMap;
auto FixPhiIncomingValues = [&](MemoryPhi *Phi, MemoryPhi *NewPhi) {
assert(Phi && NewPhi && "Invalid Phi nodes.");
BasicBlock *NewPhiBB = NewPhi->getBlock();
SmallPtrSet<BasicBlock *, 4> NewPhiBBPreds(pred_begin(NewPhiBB),
pred_end(NewPhiBB));
for (unsigned It = 0, E = Phi->getNumIncomingValues(); It < E; ++It) {
MemoryAccess *IncomingAccess = Phi->getIncomingValue(It);
BasicBlock *IncBB = Phi->getIncomingBlock(It);
if (BasicBlock *NewIncBB = cast_or_null<BasicBlock>(VMap.lookup(IncBB)))
IncBB = NewIncBB;
else if (IgnoreIncomingWithNoClones)
continue;
// Now we have IncBB, and will need to add incoming from it to NewPhi.
// If IncBB is not a predecessor of NewPhiBB, then do not add it.
// NewPhiBB was cloned without that edge.
if (!NewPhiBBPreds.count(IncBB))
continue;
// Determine incoming value and add it as incoming from IncBB.
if (MemoryUseOrDef *IncMUD = dyn_cast<MemoryUseOrDef>(IncomingAccess)) {
if (!MSSA->isLiveOnEntryDef(IncMUD)) {
Instruction *IncI = IncMUD->getMemoryInst();
assert(IncI && "Found MemoryUseOrDef with no Instruction.");
if (Instruction *NewIncI =
cast_or_null<Instruction>(VMap.lookup(IncI))) {
IncMUD = MSSA->getMemoryAccess(NewIncI);
assert(IncMUD &&
"MemoryUseOrDef cannot be null, all preds processed.");
}
}
NewPhi->addIncoming(IncMUD, IncBB);
} else {
MemoryPhi *IncPhi = cast<MemoryPhi>(IncomingAccess);
if (MemoryAccess *NewDefPhi = MPhiMap.lookup(IncPhi))
NewPhi->addIncoming(NewDefPhi, IncBB);
else
NewPhi->addIncoming(IncPhi, IncBB);
}
}
};
auto ProcessBlock = [&](BasicBlock *BB) {
BasicBlock *NewBlock = cast_or_null<BasicBlock>(VMap.lookup(BB));
if (!NewBlock)
return;
assert(!MSSA->getWritableBlockAccesses(NewBlock) &&
"Cloned block should have no accesses");
// Add MemoryPhi.
if (MemoryPhi *MPhi = MSSA->getMemoryAccess(BB)) {
MemoryPhi *NewPhi = MSSA->createMemoryPhi(NewBlock);
MPhiMap[MPhi] = NewPhi;
}
// Update Uses and Defs.
cloneUsesAndDefs(BB, NewBlock, VMap, MPhiMap);
};
for (auto BB : llvm::concat<BasicBlock *const>(LoopBlocks, ExitBlocks))
ProcessBlock(BB);
for (auto BB : llvm::concat<BasicBlock *const>(LoopBlocks, ExitBlocks))
if (MemoryPhi *MPhi = MSSA->getMemoryAccess(BB))
if (MemoryAccess *NewPhi = MPhiMap.lookup(MPhi))
FixPhiIncomingValues(MPhi, cast<MemoryPhi>(NewPhi));
}
void MemorySSAUpdater::updateForClonedBlockIntoPred(
BasicBlock *BB, BasicBlock *P1, const ValueToValueMapTy &VM) {
// All defs/phis from outside BB that are used in BB, are valid uses in P1.
// Since those defs/phis must have dominated BB, and also dominate P1.
// Defs from BB being used in BB will be replaced with the cloned defs from
// VM. The uses of BB's Phi (if it exists) in BB will be replaced by the
// incoming def into the Phi from P1.
PhiToDefMap MPhiMap;
if (MemoryPhi *MPhi = MSSA->getMemoryAccess(BB))
MPhiMap[MPhi] = MPhi->getIncomingValueForBlock(P1);
cloneUsesAndDefs(BB, P1, VM, MPhiMap);
}
template <typename Iter>
void MemorySSAUpdater::privateUpdateExitBlocksForClonedLoop(
ArrayRef<BasicBlock *> ExitBlocks, Iter ValuesBegin, Iter ValuesEnd,
DominatorTree &DT) {
SmallVector<CFGUpdate, 4> Updates;
// Update/insert phis in all successors of exit blocks.
for (auto *Exit : ExitBlocks)
for (const ValueToValueMapTy *VMap : make_range(ValuesBegin, ValuesEnd))
if (BasicBlock *NewExit = cast_or_null<BasicBlock>(VMap->lookup(Exit))) {
BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
Updates.push_back({DT.Insert, NewExit, ExitSucc});
}
applyInsertUpdates(Updates, DT);
}
void MemorySSAUpdater::updateExitBlocksForClonedLoop(
ArrayRef<BasicBlock *> ExitBlocks, const ValueToValueMapTy &VMap,
DominatorTree &DT) {
const ValueToValueMapTy *const Arr[] = {&VMap};
privateUpdateExitBlocksForClonedLoop(ExitBlocks, std::begin(Arr),
std::end(Arr), DT);
}
void MemorySSAUpdater::updateExitBlocksForClonedLoop(
ArrayRef<BasicBlock *> ExitBlocks,
ArrayRef<std::unique_ptr<ValueToValueMapTy>> VMaps, DominatorTree &DT) {
auto GetPtr = [&](const std::unique_ptr<ValueToValueMapTy> &I) {
return I.get();
};
using MappedIteratorType =
mapped_iterator<const std::unique_ptr<ValueToValueMapTy> *,
decltype(GetPtr)>;
auto MapBegin = MappedIteratorType(VMaps.begin(), GetPtr);
auto MapEnd = MappedIteratorType(VMaps.end(), GetPtr);
privateUpdateExitBlocksForClonedLoop(ExitBlocks, MapBegin, MapEnd, DT);
}
void MemorySSAUpdater::applyUpdates(ArrayRef<CFGUpdate> Updates,
DominatorTree &DT) {
SmallVector<CFGUpdate, 4> RevDeleteUpdates;
SmallVector<CFGUpdate, 4> InsertUpdates;
for (auto &Update : Updates) {
if (Update.getKind() == DT.Insert)
InsertUpdates.push_back({DT.Insert, Update.getFrom(), Update.getTo()});
else
RevDeleteUpdates.push_back({DT.Insert, Update.getFrom(), Update.getTo()});
}
if (!RevDeleteUpdates.empty()) {
// Update for inserted edges: use newDT and snapshot CFG as if deletes had
// not occured.
// FIXME: This creates a new DT, so it's more expensive to do mix
// delete/inserts vs just inserts. We can do an incremental update on the DT
// to revert deletes, than re-delete the edges. Teaching DT to do this, is
// part of a pending cleanup.
DominatorTree NewDT(DT, RevDeleteUpdates);
GraphDiff<BasicBlock *> GD(RevDeleteUpdates);
applyInsertUpdates(InsertUpdates, NewDT, &GD);
} else {
GraphDiff<BasicBlock *> GD;
applyInsertUpdates(InsertUpdates, DT, &GD);
}
// Update for deleted edges
for (auto &Update : RevDeleteUpdates)
removeEdge(Update.getFrom(), Update.getTo());
}
void MemorySSAUpdater::applyInsertUpdates(ArrayRef<CFGUpdate> Updates,
DominatorTree &DT) {
GraphDiff<BasicBlock *> GD;
applyInsertUpdates(Updates, DT, &GD);
}
void MemorySSAUpdater::applyInsertUpdates(ArrayRef<CFGUpdate> Updates,
DominatorTree &DT,
const GraphDiff<BasicBlock *> *GD) {
// Get recursive last Def, assuming well formed MSSA and updated DT.
auto GetLastDef = [&](BasicBlock *BB) -> MemoryAccess * {
while (true) {
MemorySSA::DefsList *Defs = MSSA->getWritableBlockDefs(BB);
// Return last Def or Phi in BB, if it exists.
if (Defs)
return &*(--Defs->end());
// Check number of predecessors, we only care if there's more than one.
unsigned Count = 0;
BasicBlock *Pred = nullptr;
for (auto &Pair : children<GraphDiffInvBBPair>({GD, BB})) {
Pred = Pair.second;
Count++;
if (Count == 2)
break;
}
// If BB has multiple predecessors, get last definition from IDom.
if (Count != 1) {
// [SimpleLoopUnswitch] If BB is a dead block, about to be deleted, its
// DT is invalidated. Return LoE as its last def. This will be added to
// MemoryPhi node, and later deleted when the block is deleted.
if (!DT.getNode(BB))
return MSSA->getLiveOnEntryDef();
if (auto *IDom = DT.getNode(BB)->getIDom())
if (IDom->getBlock() != BB) {
BB = IDom->getBlock();
continue;
}
return MSSA->getLiveOnEntryDef();
} else {
// Single predecessor, BB cannot be dead. GetLastDef of Pred.
assert(Count == 1 && Pred && "Single predecessor expected.");
BB = Pred;
}
};
llvm_unreachable("Unable to get last definition.");
};
// Get nearest IDom given a set of blocks.
// TODO: this can be optimized by starting the search at the node with the
// lowest level (highest in the tree).
auto FindNearestCommonDominator =
[&](const SmallSetVector<BasicBlock *, 2> &BBSet) -> BasicBlock * {
BasicBlock *PrevIDom = *BBSet.begin();
for (auto *BB : BBSet)
PrevIDom = DT.findNearestCommonDominator(PrevIDom, BB);
return PrevIDom;
};
// Get all blocks that dominate PrevIDom, stop when reaching CurrIDom. Do not
// include CurrIDom.
auto GetNoLongerDomBlocks =
[&](BasicBlock *PrevIDom, BasicBlock *CurrIDom,
SmallVectorImpl<BasicBlock *> &BlocksPrevDom) {
if (PrevIDom == CurrIDom)
return;
BlocksPrevDom.push_back(PrevIDom);
BasicBlock *NextIDom = PrevIDom;
while (BasicBlock *UpIDom =
DT.getNode(NextIDom)->getIDom()->getBlock()) {
if (UpIDom == CurrIDom)
break;
BlocksPrevDom.push_back(UpIDom);
NextIDom = UpIDom;
}
};
// Map a BB to its predecessors: added + previously existing. To get a
// deterministic order, store predecessors as SetVectors. The order in each
// will be defined by teh order in Updates (fixed) and the order given by
// children<> (also fixed). Since we further iterate over these ordered sets,
// we lose the information of multiple edges possibly existing between two
// blocks, so we'll keep and EdgeCount map for that.
// An alternate implementation could keep unordered set for the predecessors,
// traverse either Updates or children<> each time to get the deterministic
// order, and drop the usage of EdgeCount. This alternate approach would still
// require querying the maps for each predecessor, and children<> call has
// additional computation inside for creating the snapshot-graph predecessors.
// As such, we favor using a little additional storage and less compute time.
// This decision can be revisited if we find the alternative more favorable.
struct PredInfo {
SmallSetVector<BasicBlock *, 2> Added;
SmallSetVector<BasicBlock *, 2> Prev;
};
SmallDenseMap<BasicBlock *, PredInfo> PredMap;
for (auto &Edge : Updates) {
BasicBlock *BB = Edge.getTo();
auto &AddedBlockSet = PredMap[BB].Added;
AddedBlockSet.insert(Edge.getFrom());
}
// Store all existing predecessor for each BB, at least one must exist.
SmallDenseMap<std::pair<BasicBlock *, BasicBlock *>, int> EdgeCountMap;
SmallPtrSet<BasicBlock *, 2> NewBlocks;
for (auto &BBPredPair : PredMap) {
auto *BB = BBPredPair.first;
const auto &AddedBlockSet = BBPredPair.second.Added;
auto &PrevBlockSet = BBPredPair.second.Prev;
for (auto &Pair : children<GraphDiffInvBBPair>({GD, BB})) {
BasicBlock *Pi = Pair.second;
if (!AddedBlockSet.count(Pi))
PrevBlockSet.insert(Pi);
EdgeCountMap[{Pi, BB}]++;
}
if (PrevBlockSet.empty()) {
assert(pred_size(BB) == AddedBlockSet.size() && "Duplicate edges added.");
LLVM_DEBUG(
dbgs()
<< "Adding a predecessor to a block with no predecessors. "
"This must be an edge added to a new, likely cloned, block. "
"Its memory accesses must be already correct, assuming completed "
"via the updateExitBlocksForClonedLoop API. "
"Assert a single such edge is added so no phi addition or "
"additional processing is required.\n");
assert(AddedBlockSet.size() == 1 &&
"Can only handle adding one predecessor to a new block.");
// Need to remove new blocks from PredMap. Remove below to not invalidate
// iterator here.
NewBlocks.insert(BB);
}
}
// Nothing to process for new/cloned blocks.
for (auto *BB : NewBlocks)
PredMap.erase(BB);
SmallVector<BasicBlock *, 8> BlocksToProcess;
SmallVector<BasicBlock *, 16> BlocksWithDefsToReplace;
// First create MemoryPhis in all blocks that don't have one. Create in the
// order found in Updates, not in PredMap, to get deterministic numbering.
for (auto &Edge : Updates) {
BasicBlock *BB = Edge.getTo();
if (PredMap.count(BB) && !MSSA->getMemoryAccess(BB))
MSSA->createMemoryPhi(BB);
}
// Now we'll fill in the MemoryPhis with the right incoming values.
for (auto &BBPredPair : PredMap) {
auto *BB = BBPredPair.first;
const auto &PrevBlockSet = BBPredPair.second.Prev;
const auto &AddedBlockSet = BBPredPair.second.Added;
assert(!PrevBlockSet.empty() &&
"At least one previous predecessor must exist.");
// TODO: if this becomes a bottleneck, we can save on GetLastDef calls by
// keeping this map before the loop. We can reuse already populated entries
// if an edge is added from the same predecessor to two different blocks,
// and this does happen in rotate. Note that the map needs to be updated
// when deleting non-necessary phis below, if the phi is in the map by
// replacing the value with DefP1.
SmallDenseMap<BasicBlock *, MemoryAccess *> LastDefAddedPred;
for (auto *AddedPred : AddedBlockSet) {
auto *DefPn = GetLastDef(AddedPred);
assert(DefPn != nullptr && "Unable to find last definition.");
LastDefAddedPred[AddedPred] = DefPn;
}
MemoryPhi *NewPhi = MSSA->getMemoryAccess(BB);
// If Phi is not empty, add an incoming edge from each added pred. Must
// still compute blocks with defs to replace for this block below.
if (NewPhi->getNumOperands()) {
for (auto *Pred : AddedBlockSet) {
auto *LastDefForPred = LastDefAddedPred[Pred];
for (int I = 0, E = EdgeCountMap[{Pred, BB}]; I < E; ++I)
NewPhi->addIncoming(LastDefForPred, Pred);
}
} else {
// Pick any existing predecessor and get its definition. All other
// existing predecessors should have the same one, since no phi existed.
auto *P1 = *PrevBlockSet.begin();
MemoryAccess *DefP1 = GetLastDef(P1);
// Check DefP1 against all Defs in LastDefPredPair. If all the same,
// nothing to add.
bool InsertPhi = false;
for (auto LastDefPredPair : LastDefAddedPred)
if (DefP1 != LastDefPredPair.second) {
InsertPhi = true;
break;
}
if (!InsertPhi) {
// Since NewPhi may be used in other newly added Phis, replace all uses
// of NewPhi with the definition coming from all predecessors (DefP1),
// before deleting it.
NewPhi->replaceAllUsesWith(DefP1);
removeMemoryAccess(NewPhi);
continue;
}
// Update Phi with new values for new predecessors and old value for all
// other predecessors. Since AddedBlockSet and PrevBlockSet are ordered
// sets, the order of entries in NewPhi is deterministic.
for (auto *Pred : AddedBlockSet) {
auto *LastDefForPred = LastDefAddedPred[Pred];
for (int I = 0, E = EdgeCountMap[{Pred, BB}]; I < E; ++I)
NewPhi->addIncoming(LastDefForPred, Pred);
}
for (auto *Pred : PrevBlockSet)
for (int I = 0, E = EdgeCountMap[{Pred, BB}]; I < E; ++I)
NewPhi->addIncoming(DefP1, Pred);
// Insert BB in the set of blocks that now have definition. We'll use this
// to compute IDF and add Phis there next.
BlocksToProcess.push_back(BB);
}
// Get all blocks that used to dominate BB and no longer do after adding
// AddedBlockSet, where PrevBlockSet are the previously known predecessors.
assert(DT.getNode(BB)->getIDom() && "BB does not have valid idom");
BasicBlock *PrevIDom = FindNearestCommonDominator(PrevBlockSet);
assert(PrevIDom && "Previous IDom should exists");
BasicBlock *NewIDom = DT.getNode(BB)->getIDom()->getBlock();
assert(NewIDom && "BB should have a new valid idom");
assert(DT.dominates(NewIDom, PrevIDom) &&
"New idom should dominate old idom");
GetNoLongerDomBlocks(PrevIDom, NewIDom, BlocksWithDefsToReplace);
}
// Compute IDF and add Phis in all IDF blocks that do not have one.
SmallVector<BasicBlock *, 32> IDFBlocks;
if (!BlocksToProcess.empty()) {
ForwardIDFCalculator IDFs(DT);
SmallPtrSet<BasicBlock *, 16> DefiningBlocks(BlocksToProcess.begin(),
BlocksToProcess.end());
IDFs.setDefiningBlocks(DefiningBlocks);
IDFs.calculate(IDFBlocks);
for (auto *BBIDF : IDFBlocks) {
if (auto *IDFPhi = MSSA->getMemoryAccess(BBIDF)) {
// Update existing Phi.
// FIXME: some updates may be redundant, try to optimize and skip some.
for (unsigned I = 0, E = IDFPhi->getNumIncomingValues(); I < E; ++I)
IDFPhi->setIncomingValue(I, GetLastDef(IDFPhi->getIncomingBlock(I)));
} else {
IDFPhi = MSSA->createMemoryPhi(BBIDF);
for (auto &Pair : children<GraphDiffInvBBPair>({GD, BBIDF})) {
BasicBlock *Pi = Pair.second;
IDFPhi->addIncoming(GetLastDef(Pi), Pi);
}
}
}
}
// Now for all defs in BlocksWithDefsToReplace, if there are uses they no
// longer dominate, replace those with the closest dominating def.
// This will also update optimized accesses, as they're also uses.
for (auto *BlockWithDefsToReplace : BlocksWithDefsToReplace) {
if (auto DefsList = MSSA->getWritableBlockDefs(BlockWithDefsToReplace)) {
for (auto &DefToReplaceUses : *DefsList) {
BasicBlock *DominatingBlock = DefToReplaceUses.getBlock();
Value::use_iterator UI = DefToReplaceUses.use_begin(),
E = DefToReplaceUses.use_end();
for (; UI != E;) {
Use &U = *UI;
++UI;
MemoryAccess *Usr = dyn_cast<MemoryAccess>(U.getUser());
if (MemoryPhi *UsrPhi = dyn_cast<MemoryPhi>(Usr)) {
BasicBlock *DominatedBlock = UsrPhi->getIncomingBlock(U);
if (!DT.dominates(DominatingBlock, DominatedBlock))
U.set(GetLastDef(DominatedBlock));
} else {
BasicBlock *DominatedBlock = Usr->getBlock();
if (!DT.dominates(DominatingBlock, DominatedBlock)) {
if (auto *DomBlPhi = MSSA->getMemoryAccess(DominatedBlock))
U.set(DomBlPhi);
else {
auto *IDom = DT.getNode(DominatedBlock)->getIDom();
assert(IDom && "Block must have a valid IDom.");
U.set(GetLastDef(IDom->getBlock()));
}
cast<MemoryUseOrDef>(Usr)->resetOptimized();
}
}
}
}
}
}
}
// Move What before Where in the MemorySSA IR.
template <class WhereType>
void MemorySSAUpdater::moveTo(MemoryUseOrDef *What, BasicBlock *BB,
WhereType Where) {
// Mark MemoryPhi users of What not to be optimized.
for (auto *U : What->users())
if (MemoryPhi *PhiUser = dyn_cast<MemoryPhi>(U))
NonOptPhis.insert(PhiUser);
// Replace all our users with our defining access.
What->replaceAllUsesWith(What->getDefiningAccess());
// Let MemorySSA take care of moving it around in the lists.
MSSA->moveTo(What, BB, Where);
// Now reinsert it into the IR and do whatever fixups needed.
if (auto *MD = dyn_cast<MemoryDef>(What))
insertDef(MD);
else
insertUse(cast<MemoryUse>(What));
// Clear dangling pointers. We added all MemoryPhi users, but not all
// of them are removed by fixupDefs().
NonOptPhis.clear();
}
// Move What before Where in the MemorySSA IR.
void MemorySSAUpdater::moveBefore(MemoryUseOrDef *What, MemoryUseOrDef *Where) {
moveTo(What, Where->getBlock(), Where->getIterator());
}
// Move What after Where in the MemorySSA IR.
void MemorySSAUpdater::moveAfter(MemoryUseOrDef *What, MemoryUseOrDef *Where) {
moveTo(What, Where->getBlock(), ++Where->getIterator());
}
void MemorySSAUpdater::moveToPlace(MemoryUseOrDef *What, BasicBlock *BB,
MemorySSA::InsertionPlace Where) {
return moveTo(What, BB, Where);
}
// All accesses in To used to be in From. Move to end and update access lists.
void MemorySSAUpdater::moveAllAccesses(BasicBlock *From, BasicBlock *To,
Instruction *Start) {
MemorySSA::AccessList *Accs = MSSA->getWritableBlockAccesses(From);
if (!Accs)
return;
MemoryAccess *FirstInNew = nullptr;
for (Instruction &I : make_range(Start->getIterator(), To->end()))
if ((FirstInNew = MSSA->getMemoryAccess(&I)))
break;
if (!FirstInNew)
return;
auto *MUD = cast<MemoryUseOrDef>(FirstInNew);
do {
auto NextIt = ++MUD->getIterator();
MemoryUseOrDef *NextMUD = (!Accs || NextIt == Accs->end())
? nullptr
: cast<MemoryUseOrDef>(&*NextIt);
MSSA->moveTo(MUD, To, MemorySSA::End);
// Moving MUD from Accs in the moveTo above, may delete Accs, so we need to
// retrieve it again.
Accs = MSSA->getWritableBlockAccesses(From);
MUD = NextMUD;
} while (MUD);
}
void MemorySSAUpdater::moveAllAfterSpliceBlocks(BasicBlock *From,
BasicBlock *To,
Instruction *Start) {
assert(MSSA->getBlockAccesses(To) == nullptr &&
"To block is expected to be free of MemoryAccesses.");
moveAllAccesses(From, To, Start);
for (BasicBlock *Succ : successors(To))
if (MemoryPhi *MPhi = MSSA->getMemoryAccess(Succ))
MPhi->setIncomingBlock(MPhi->getBasicBlockIndex(From), To);
}
void MemorySSAUpdater::moveAllAfterMergeBlocks(BasicBlock *From, BasicBlock *To,
Instruction *Start) {
assert(From->getSinglePredecessor() == To &&
"From block is expected to have a single predecessor (To).");
moveAllAccesses(From, To, Start);
for (BasicBlock *Succ : successors(From))
if (MemoryPhi *MPhi = MSSA->getMemoryAccess(Succ))
MPhi->setIncomingBlock(MPhi->getBasicBlockIndex(From), To);
}
/// If all arguments of a MemoryPHI are defined by the same incoming
/// argument, return that argument.
static MemoryAccess *onlySingleValue(MemoryPhi *MP) {
MemoryAccess *MA = nullptr;
for (auto &Arg : MP->operands()) {
if (!MA)
MA = cast<MemoryAccess>(Arg);
else if (MA != Arg)
return nullptr;
}
return MA;
}
void MemorySSAUpdater::wireOldPredecessorsToNewImmediatePredecessor(
BasicBlock *Old, BasicBlock *New, ArrayRef<BasicBlock *> Preds,
bool IdenticalEdgesWereMerged) {
assert(!MSSA->getWritableBlockAccesses(New) &&
"Access list should be null for a new block.");
MemoryPhi *Phi = MSSA->getMemoryAccess(Old);
if (!Phi)
return;
if (Old->hasNPredecessors(1)) {
assert(pred_size(New) == Preds.size() &&
"Should have moved all predecessors.");
MSSA->moveTo(Phi, New, MemorySSA::Beginning);
} else {
assert(!Preds.empty() && "Must be moving at least one predecessor to the "
"new immediate predecessor.");
MemoryPhi *NewPhi = MSSA->createMemoryPhi(New);
SmallPtrSet<BasicBlock *, 16> PredsSet(Preds.begin(), Preds.end());
// Currently only support the case of removing a single incoming edge when
// identical edges were not merged.
if (!IdenticalEdgesWereMerged)
assert(PredsSet.size() == Preds.size() &&
"If identical edges were not merged, we cannot have duplicate "
"blocks in the predecessors");
Phi->unorderedDeleteIncomingIf([&](MemoryAccess *MA, BasicBlock *B) {
if (PredsSet.count(B)) {
NewPhi->addIncoming(MA, B);
if (!IdenticalEdgesWereMerged)
PredsSet.erase(B);
return true;
}
return false;
});
Phi->addIncoming(NewPhi, New);
if (onlySingleValue(NewPhi))
removeMemoryAccess(NewPhi);
}
}
void MemorySSAUpdater::removeMemoryAccess(MemoryAccess *MA) {
assert(!MSSA->isLiveOnEntryDef(MA) &&
"Trying to remove the live on entry def");
// We can only delete phi nodes if they have no uses, or we can replace all
// uses with a single definition.
MemoryAccess *NewDefTarget = nullptr;
if (MemoryPhi *MP = dyn_cast<MemoryPhi>(MA)) {
// Note that it is sufficient to know that all edges of the phi node have
// the same argument. If they do, by the definition of dominance frontiers
// (which we used to place this phi), that argument must dominate this phi,
// and thus, must dominate the phi's uses, and so we will not hit the assert
// below.
NewDefTarget = onlySingleValue(MP);
assert((NewDefTarget || MP->use_empty()) &&
"We can't delete this memory phi");
} else {
NewDefTarget = cast<MemoryUseOrDef>(MA)->getDefiningAccess();
}
// Re-point the uses at our defining access
if (!isa<MemoryUse>(MA) && !MA->use_empty()) {
// Reset optimized on users of this store, and reset the uses.
// A few notes:
// 1. This is a slightly modified version of RAUW to avoid walking the
// uses twice here.
// 2. If we wanted to be complete, we would have to reset the optimized
// flags on users of phi nodes if doing the below makes a phi node have all
// the same arguments. Instead, we prefer users to removeMemoryAccess those
// phi nodes, because doing it here would be N^3.
if (MA->hasValueHandle())
ValueHandleBase::ValueIsRAUWd(MA, NewDefTarget);
// Note: We assume MemorySSA is not used in metadata since it's not really
// part of the IR.
while (!MA->use_empty()) {
Use &U = *MA->use_begin();
if (auto *MUD = dyn_cast<MemoryUseOrDef>(U.getUser()))
MUD->resetOptimized();
U.set(NewDefTarget);
}
}
// The call below to erase will destroy MA, so we can't change the order we
// are doing things here
MSSA->removeFromLookups(MA);
MSSA->removeFromLists(MA);
}
void MemorySSAUpdater::removeBlocks(
const SmallPtrSetImpl<BasicBlock *> &DeadBlocks) {
// First delete all uses of BB in MemoryPhis.
for (BasicBlock *BB : DeadBlocks) {
Instruction *TI = BB->getTerminator();
assert(TI && "Basic block expected to have a terminator instruction");
for (BasicBlock *Succ : successors(TI))
if (!DeadBlocks.count(Succ))
if (MemoryPhi *MP = MSSA->getMemoryAccess(Succ)) {
MP->unorderedDeleteIncomingBlock(BB);
if (MP->getNumIncomingValues() == 1)
removeMemoryAccess(MP);
}
// Drop all references of all accesses in BB
if (MemorySSA::AccessList *Acc = MSSA->getWritableBlockAccesses(BB))
for (MemoryAccess &MA : *Acc)
MA.dropAllReferences();
}
// Next, delete all memory accesses in each block
for (BasicBlock *BB : DeadBlocks) {
MemorySSA::AccessList *Acc = MSSA->getWritableBlockAccesses(BB);
if (!Acc)
continue;
for (auto AB = Acc->begin(), AE = Acc->end(); AB != AE;) {
MemoryAccess *MA = &*AB;
++AB;
MSSA->removeFromLookups(MA);
MSSA->removeFromLists(MA);
}
}
}
MemoryAccess *MemorySSAUpdater::createMemoryAccessInBB(
Instruction *I, MemoryAccess *Definition, const BasicBlock *BB,
MemorySSA::InsertionPlace Point) {
MemoryUseOrDef *NewAccess = MSSA->createDefinedAccess(I, Definition);
MSSA->insertIntoListsForBlock(NewAccess, BB, Point);
return NewAccess;
}
MemoryUseOrDef *MemorySSAUpdater::createMemoryAccessBefore(
Instruction *I, MemoryAccess *Definition, MemoryUseOrDef *InsertPt) {
assert(I->getParent() == InsertPt->getBlock() &&
"New and old access must be in the same block");
MemoryUseOrDef *NewAccess = MSSA->createDefinedAccess(I, Definition);
MSSA->insertIntoListsBefore(NewAccess, InsertPt->getBlock(),
InsertPt->getIterator());
return NewAccess;
}
MemoryUseOrDef *MemorySSAUpdater::createMemoryAccessAfter(
Instruction *I, MemoryAccess *Definition, MemoryAccess *InsertPt) {
assert(I->getParent() == InsertPt->getBlock() &&
"New and old access must be in the same block");
MemoryUseOrDef *NewAccess = MSSA->createDefinedAccess(I, Definition);
MSSA->insertIntoListsBefore(NewAccess, InsertPt->getBlock(),
++InsertPt->getIterator());
return NewAccess;
}
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