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AArch64: Don't modify other modules in AArch64PromoteConstant 

Avoid modifying other modules in `AArch64PromoteConstant` when the
constant is `ConstantData` (a horrible accident, I'm sure, caught by an
experimental follow-up to r261464).

Previously, this walked through all the users of a constant, but that
reaches into other modules when the constant doesn't depend transitively
on a `GlobalValue`!  Since we're walking instructions anyway, just
modify the instructions we actually see.

As a drive-by, instead of storing `Use` and getting the instructions
again via `Use::getUser()` (which is not a constantant time lookup),
store `std::pair<Instruction, unsigned>`.  Besides being cheaper, this
makes it easier to drop use-lists form `ConstantData` in the future.
(I threw this in because I was touching all the code anyway.)

Because the patch completely changes the traversal logic, it looks
like a rewrite of the pass, but the core logic is all the same (or
should be, minus the out-of-module changes).  In other words, there
should be NFC as long as the LLVMContext only has a single Module.

I didn't think of a good way to test this, but I hope to submit a patch
eventually that makes walking these use-lists illegal/impossible.

llvm-svn: 263853
This commit is contained in:
Duncan P. N. Exon Smith 2016-03-18 23:30:54 +00:00
parent 759aca01ce
commit c3fa1eded2
1 changed files with 196 additions and 167 deletions
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363
llvm/lib/Target/AArch64/AArch64PromoteConstant.cpp
View File

@ -85,6 +85,21 @@ namespace {
class AArch64PromoteConstant : public ModulePass {
public:
struct PromotedConstant {
bool ShouldConvert = false;
GlobalVariable *GV = nullptr;
};
typedef SmallDenseMap<Constant *, PromotedConstant, 16> PromotionCacheTy;
struct UpdateRecord {
Constant *C;
Instruction *User;
unsigned Op;
UpdateRecord(Constant *C, Instruction *User, unsigned Op)
: C(C), User(User), Op(Op) {}
};
static char ID;
AArch64PromoteConstant() : ModulePass(ID) {}
@ -95,8 +110,9 @@ public:
bool runOnModule(Module &M) override {
DEBUG(dbgs() << getPassName() << '\n');
bool Changed = false;
PromotionCacheTy PromotionCache;
for (auto &MF : M) {
Changed |= runOnFunction(MF);
Changed |= runOnFunction(MF, PromotionCache);
}
return Changed;
}
@ -105,7 +121,7 @@ private:
/// Look for interesting constants used within the given function.
/// Promote them into global variables, load these global variables within
/// the related function, so that the number of inserted load is minimal.
bool runOnFunction(Function &F);
bool runOnFunction(Function &F, PromotionCacheTy &PromotionCache);
// This transformation requires dominator info
void getAnalysisUsage(AnalysisUsage &AU) const override {
@ -115,15 +131,12 @@ private:
}
/// Type to store a list of Uses.
typedef SmallVector<Use *, 4> Uses;
typedef SmallVector<std::pair<Instruction *, unsigned>, 4> Uses;
/// Map an insertion point to all the uses it dominates.
typedef DenseMap<Instruction *, Uses> InsertionPoints;
/// Map a function to the required insertion point of load for a
/// global variable.
typedef DenseMap<Function *, InsertionPoints> InsertionPointsPerFunc;
/// Find the closest point that dominates the given Use.
Instruction *findInsertionPoint(Use &Use);
Instruction *findInsertionPoint(Instruction &User, unsigned OpNo);
/// Check if the given insertion point is dominated by an existing
/// insertion point.
@ -135,7 +148,8 @@ private:
/// \pre NewPt and all instruction in InsertPts belong to the same function
/// \return true if one of the insertion point in InsertPts dominates NewPt,
/// false otherwise
bool isDominated(Instruction *NewPt, Use &Use, InsertionPoints &InsertPts);
bool isDominated(Instruction *NewPt, Instruction *User, unsigned OpNo,
InsertionPoints &InsertPts);
/// Check if the given insertion point can be merged with an existing
/// insertion point in a common dominator.
@ -149,7 +163,8 @@ private:
/// \return true if it exists an insertion point in InsertPts that could
/// have been merged with NewPt in a common dominator,
/// false otherwise
bool tryAndMerge(Instruction *NewPt, Use &Use, InsertionPoints &InsertPts);
bool tryAndMerge(Instruction *NewPt, Instruction *User, unsigned OpNo,
InsertionPoints &InsertPts);
/// Compute the minimal insertion points to dominates all the interesting
/// uses of value.
@ -157,37 +172,31 @@ private:
/// contains a list of all the uses it dominates within the related function
/// \param Val constant to be examined
/// \param[out] InsPtsPerFunc output storage of the analysis
void computeInsertionPoints(Constant *Val,
InsertionPointsPerFunc &InsPtsPerFunc);
void computeInsertionPoint(Instruction *User, unsigned OpNo,
InsertionPoints &InsertPts);
/// Insert a definition of a new global variable at each point contained in
/// InsPtsPerFunc and update the related uses (also contained in
/// InsPtsPerFunc).
bool insertDefinitions(Constant *Cst, InsertionPointsPerFunc &InsPtsPerFunc);
void insertDefinitions(Function &F, GlobalVariable &GV,
InsertionPoints &InsertPts);
/// Compute the minimal insertion points to dominate all the interesting
/// uses of Val and insert a definition of a new global variable
/// at these points.
/// Also update the uses of Val accordingly.
/// Currently a use of Val is considered interesting if:
/// - Val is not UndefValue
/// - Val is not zeroinitialized
/// - Replacing Val per a load of a global variable is valid.
/// \see shouldConvert for more details
bool computeAndInsertDefinitions(Constant *Val);
/// Sort the updates in a deterministic way.
void sortUpdates(SmallVectorImpl<UpdateRecord> &Updates);
/// Promote the given constant into a global variable if it is expected to
/// be profitable.
/// \return true if Cst has been promoted
bool promoteConstant(Constant *Cst);
/// Do the constant promotion indicated by the Updates records, keeping track
/// of globals in PromotionCache.
void promoteConstants(Function &F, SmallVectorImpl<UpdateRecord> &Updates,
PromotionCacheTy &PromotionCache);
/// Transfer the list of dominated uses of IPI to NewPt in InsertPts.
/// Append Use to this list and delete the entry of IPI in InsertPts.
static void appendAndTransferDominatedUses(Instruction *NewPt, Use &Use,
static void appendAndTransferDominatedUses(Instruction *NewPt,
Instruction *User, unsigned OpNo,
InsertionPoints::iterator &IPI,
InsertionPoints &InsertPts) {
// Record the dominated use.
IPI->second.push_back(&Use);
IPI->second.emplace_back(User, OpNo);
// Transfer the dominated uses of IPI to NewPt
// Inserting into the DenseMap may invalidate existing iterator.
// Keep a copy of the key to find the iterator to erase. Keep a copy of the
@ -302,7 +311,7 @@ static bool shouldConvertUse(const Constant *Cst, const Instruction *Instr,
/// for the regular approach, even for float).
/// Again, the simplest solution would be to promote every
/// constant and rematerialize them when they are actually cheap to create.
static bool shouldConvert(const Constant *Cst) {
static bool shouldConvertImpl(const Constant *Cst) {
if (isa<const UndefValue>(Cst))
return false;
@ -325,18 +334,28 @@ static bool shouldConvert(const Constant *Cst) {
return isConstantUsingVectorTy(Cst->getType());
}
Instruction *AArch64PromoteConstant::findInsertionPoint(Use &Use) {
Instruction *User = cast<Instruction>(Use.getUser());
// If this user is a phi, the insertion point is in the related
// incoming basic block.
if (PHINode *PhiInst = dyn_cast<PHINode>(User))
return PhiInst->getIncomingBlock(Use.getOperandNo())->getTerminator();
return User;
static bool
shouldConvert(Constant &C,
AArch64PromoteConstant::PromotionCacheTy &PromotionCache) {
auto Converted = PromotionCache.insert(
std::make_pair(&C, AArch64PromoteConstant::PromotedConstant()));
if (Converted.second)
Converted.first->second.ShouldConvert = shouldConvertImpl(&C);
return Converted.first->second.ShouldConvert;
}
bool AArch64PromoteConstant::isDominated(Instruction *NewPt, Use &Use,
Instruction *AArch64PromoteConstant::findInsertionPoint(Instruction &User,
unsigned OpNo) {
// If this user is a phi, the insertion point is in the related
// incoming basic block.
if (PHINode *PhiInst = dyn_cast<PHINode>(&User))
return PhiInst->getIncomingBlock(OpNo)->getTerminator();
return &User;
}
bool AArch64PromoteConstant::isDominated(Instruction *NewPt, Instruction *User,
unsigned OpNo,
InsertionPoints &InsertPts) {
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(
@ -355,14 +374,15 @@ bool AArch64PromoteConstant::isDominated(Instruction *NewPt, Use &Use,
DEBUG(dbgs() << "Insertion point dominated by:\n");
DEBUG(IPI.first->print(dbgs()));
DEBUG(dbgs() << '\n');
IPI.second.push_back(&Use);
IPI.second.emplace_back(User, OpNo);
return true;
}
}
return false;
}
bool AArch64PromoteConstant::tryAndMerge(Instruction *NewPt, Use &Use,
bool AArch64PromoteConstant::tryAndMerge(Instruction *NewPt, Instruction *User,
unsigned OpNo,
InsertionPoints &InsertPts) {
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(
*NewPt->getParent()->getParent()).getDomTree();
@ -382,7 +402,7 @@ bool AArch64PromoteConstant::tryAndMerge(Instruction *NewPt, Use &Use,
DEBUG(dbgs() << "Merge insertion point with:\n");
DEBUG(IPI->first->print(dbgs()));
DEBUG(dbgs() << "\nat considered insertion point.\n");
appendAndTransferDominatedUses(NewPt, Use, IPI, InsertPts);
appendAndTransferDominatedUses(NewPt, User, OpNo, IPI, InsertPts);
return true;
}
@ -406,149 +426,158 @@ bool AArch64PromoteConstant::tryAndMerge(Instruction *NewPt, Use &Use,
DEBUG(dbgs() << '\n');
DEBUG(NewPt->print(dbgs()));
DEBUG(dbgs() << '\n');
appendAndTransferDominatedUses(NewPt, Use, IPI, InsertPts);
appendAndTransferDominatedUses(NewPt, User, OpNo, IPI, InsertPts);
return true;
}
return false;
}
void AArch64PromoteConstant::computeInsertionPoints(
Constant *Val, InsertionPointsPerFunc &InsPtsPerFunc) {
DEBUG(dbgs() << "** Compute insertion points **\n");
for (Use &Use : Val->uses()) {
Instruction *User = dyn_cast<Instruction>(Use.getUser());
// If the user is not an Instruction, we cannot modify it.
if (!User)
continue;
// Filter out uses that should not be converted.
if (!shouldConvertUse(Val, User, Use.getOperandNo()))
continue;
DEBUG(dbgs() << "Considered use, opidx " << Use.getOperandNo() << ":\n");
DEBUG(User->print(dbgs()));
DEBUG(dbgs() << '\n');
Instruction *InsertionPoint = findInsertionPoint(Use);
DEBUG(dbgs() << "Considered insertion point:\n");
DEBUG(InsertionPoint->print(dbgs()));
DEBUG(dbgs() << '\n');
// Check if the current insertion point is useless, i.e., it is dominated
// by another one.
InsertionPoints &InsertPts =
InsPtsPerFunc[InsertionPoint->getParent()->getParent()];
if (isDominated(InsertionPoint, Use, InsertPts))
continue;
// This insertion point is useful, check if we can merge some insertion
// point in a common dominator or if NewPt dominates an existing one.
if (tryAndMerge(InsertionPoint, Use, InsertPts))
continue;
DEBUG(dbgs() << "Keep considered insertion point\n");
// It is definitely useful by its own
InsertPts[InsertionPoint].push_back(&Use);
}
}
bool AArch64PromoteConstant::insertDefinitions(
Constant *Cst, InsertionPointsPerFunc &InsPtsPerFunc) {
// We will create one global variable per Module.
DenseMap<Module *, GlobalVariable *> ModuleToMergedGV;
bool HasChanged = false;
// Traverse all insertion points in all the function.
for (const auto &FctToInstPtsIt : InsPtsPerFunc) {
const InsertionPoints &InsertPts = FctToInstPtsIt.second;
// Do more checking for debug purposes.
#ifndef NDEBUG
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(
*FctToInstPtsIt.first).getDomTree();
#endif
assert(!InsertPts.empty() && "Empty uses does not need a definition");
Module *M = FctToInstPtsIt.first->getParent();
GlobalVariable *&PromotedGV = ModuleToMergedGV[M];
if (!PromotedGV) {
PromotedGV = new GlobalVariable(
*M, Cst->getType(), true, GlobalValue::InternalLinkage, nullptr,
"_PromotedConst", nullptr, GlobalVariable::NotThreadLocal);
PromotedGV->setInitializer(Cst);
DEBUG(dbgs() << "Global replacement: ");
DEBUG(PromotedGV->print(dbgs()));
DEBUG(dbgs() << '\n');
++NumPromoted;
HasChanged = true;
}
for (const auto &IPI : InsertPts) {
// Create the load of the global variable.
IRBuilder<> Builder(IPI.first);
LoadInst *LoadedCst = Builder.CreateLoad(PromotedGV);
DEBUG(dbgs() << "**********\n");
DEBUG(dbgs() << "New def: ");
DEBUG(LoadedCst->print(dbgs()));
DEBUG(dbgs() << '\n');
// Update the dominated uses.
for (Use *Use : IPI.second) {
#ifndef NDEBUG
assert(DT.dominates(LoadedCst, findInsertionPoint(*Use)) &&
"Inserted definition does not dominate all its uses!");
#endif
DEBUG(dbgs() << "Use to update " << Use->getOperandNo() << ":");
DEBUG(Use->getUser()->print(dbgs()));
DEBUG(dbgs() << '\n');
Use->set(LoadedCst);
++NumPromotedUses;
}
}
}
return HasChanged;
}
bool AArch64PromoteConstant::computeAndInsertDefinitions(Constant *Val) {
InsertionPointsPerFunc InsertPtsPerFunc;
computeInsertionPoints(Val, InsertPtsPerFunc);
return insertDefinitions(Val, InsertPtsPerFunc);
}
bool AArch64PromoteConstant::promoteConstant(Constant *Cst) {
assert(Cst && "Given variable is not a valid constant.");
if (!shouldConvert(Cst))
return false;
DEBUG(dbgs() << "******************************\n");
DEBUG(dbgs() << "Candidate constant: ");
DEBUG(Cst->print(dbgs()));
void AArch64PromoteConstant::computeInsertionPoint(
Instruction *User, unsigned OpNo, InsertionPoints &InsertPts) {
DEBUG(dbgs() << "Considered use, opidx " << OpNo << ":\n");
DEBUG(User->print(dbgs()));
DEBUG(dbgs() << '\n');
return computeAndInsertDefinitions(Cst);
Instruction *InsertionPoint = findInsertionPoint(*User, OpNo);
DEBUG(dbgs() << "Considered insertion point:\n");
DEBUG(InsertionPoint->print(dbgs()));
DEBUG(dbgs() << '\n');
if (isDominated(InsertionPoint, User, OpNo, InsertPts))
return;
// This insertion point is useful, check if we can merge some insertion
// point in a common dominator or if NewPt dominates an existing one.
if (tryAndMerge(InsertionPoint, User, OpNo, InsertPts))
return;
DEBUG(dbgs() << "Keep considered insertion point\n");
// It is definitely useful by its own
InsertPts[InsertionPoint].emplace_back(User, OpNo);
}
bool AArch64PromoteConstant::runOnFunction(Function &F) {
static void ensurePromotedGV(Function &F, Constant &C,
AArch64PromoteConstant::PromotedConstant &PC) {
assert(PC.ShouldConvert &&
"Expected that we should convert this to a global");
if (PC.GV)
return;
PC.GV = new GlobalVariable(
*F.getParent(), C.getType(), true, GlobalValue::InternalLinkage, nullptr,
"_PromotedConst", nullptr, GlobalVariable::NotThreadLocal);
PC.GV->setInitializer(&C);
DEBUG(dbgs() << "Global replacement: ");
DEBUG(PC.GV->print(dbgs()));
DEBUG(dbgs() << '\n');
++NumPromoted;
}
void AArch64PromoteConstant::insertDefinitions(Function &F,
GlobalVariable &PromotedGV,
InsertionPoints &InsertPts) {
#ifndef NDEBUG
// Do more checking for debug purposes.
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
#endif
assert(!InsertPts.empty() && "Empty uses does not need a definition");
for (const auto &IPI : InsertPts) {
// Create the load of the global variable.
IRBuilder<> Builder(IPI.first);
LoadInst *LoadedCst = Builder.CreateLoad(&PromotedGV);
DEBUG(dbgs() << "**********\n");
DEBUG(dbgs() << "New def: ");
DEBUG(LoadedCst->print(dbgs()));
DEBUG(dbgs() << '\n');
// Update the dominated uses.
for (auto Use : IPI.second) {
#ifndef NDEBUG
assert(DT.dominates(LoadedCst,
findInsertionPoint(*Use.first, Use.second)) &&
"Inserted definition does not dominate all its uses!");
#endif
DEBUG({
dbgs() << "Use to update " << Use.second << ":";
Use.first->print(dbgs());
dbgs() << '\n';
});
Use.first->setOperand(Use.second, LoadedCst);
++NumPromotedUses;
}
}
}
void AArch64PromoteConstant::sortUpdates(
SmallVectorImpl<UpdateRecord> &Updates) {
// The order the constants were inserted is deterministic (unlike their
// address).
SmallDenseMap<const Constant *, unsigned, 128> InsertionOrder;
for (const auto &Record : Updates)
InsertionOrder.insert(std::make_pair(Record.C, InsertionOrder.size()));
// This is already sorted by Instruction ordering in the function and operand
// number, which is a good first step. Now reorder by constant.
std::stable_sort(
Updates.begin(), Updates.end(),
[&InsertionOrder](const UpdateRecord &L, const UpdateRecord &R) {
return InsertionOrder.lookup(L.C) < InsertionOrder.lookup(R.C);
});
}
void AArch64PromoteConstant::promoteConstants(
Function &F, SmallVectorImpl<UpdateRecord> &Updates,
PromotionCacheTy &PromotionCache) {
// Promote the constants.
for (auto U = Updates.begin(), E = Updates.end(); U != E;) {
DEBUG(dbgs() << "** Compute insertion points **\n");
auto First = U;
Constant *C = First->C;
InsertionPoints InsertPts;
do {
computeInsertionPoint(U->User, U->Op, InsertPts);
} while (++U != E && U->C == C);
auto &Promotion = PromotionCache[C];
ensurePromotedGV(F, *C, Promotion);
insertDefinitions(F, *Promotion.GV, InsertPts);
}
}
bool AArch64PromoteConstant::runOnFunction(Function &F,
PromotionCacheTy &PromotionCache) {
// Look for instructions using constant vector. Promote that constant to a
// global variable. Create as few loads of this variable as possible and
// update the uses accordingly.
bool LocalChange = false;
SmallPtrSet<Constant *, 8> AlreadyChecked;
SmallVector<UpdateRecord, 64> Updates;
for (Instruction &I : instructions(&F)) {
// Traverse the operand, looking for constant vectors. Replace them by a
// load of a global variable of constant vector type.
for (Value *Op : I.operand_values()) {
Constant *Cst = dyn_cast<Constant>(Op);
for (Use &U : I.operands()) {
Constant *Cst = dyn_cast<Constant>(U);
// There is no point in promoting global values as they are already
// global. Do not promote constant expressions either, as they may
// require some code expansion.
if (Cst && !isa<GlobalValue>(Cst) && !isa<ConstantExpr>(Cst) &&
AlreadyChecked.insert(Cst).second)
LocalChange |= promoteConstant(Cst);
if (!Cst || isa<GlobalValue>(Cst) || isa<ConstantExpr>(Cst))
continue;
// Check if this constant is worth promoting.
if (!shouldConvert(*Cst, PromotionCache))
continue;
// Check if this use should be promoted.
unsigned OpNo = &U - I.op_begin();
if (!shouldConvertUse(Cst, &I, OpNo))
continue;
Updates.emplace_back(Cst, &I, OpNo);
}
}
return LocalChange;
if (Updates.empty())
return false;
promoteConstants(F, Updates, PromotionCache);
return true;
}