//
// This pass also handles aggregate arguments that are passed into a function,
// scalarizing them if the elements of the aggregate are only loaded. Note that
-// by default it refuses to scalarize aggregates which would require passing in more than
-// three operands to the function, because passing thousands of operands for a
-// large array or structure is unprofitable! This limit is can be configured or
-// disabled, however.
+// by default it refuses to scalarize aggregates which would require passing in
+// more than three operands to the function, because passing thousands of
+// operands for a large array or structure is unprofitable! This limit is can be
+// configured or disabled, however.
//
// Note that this transformation could also be done for arguments that are only
// stored to (returning the value instead), but does not currently. This case
static char ID; // Pass identification, replacement for typeid
ArgPromotion(unsigned maxElements = 3) : CallGraphSCCPass((intptr_t)&ID),
maxElements(maxElements) {}
+
+ /// A vector used to hold the indices of a single GEP instruction
+ typedef std::vector<uint64_t> IndicesVector;
private:
bool PromoteArguments(CallGraphNode *CGN);
return true;
}
+/// Returns true if Prefix is a prefix of longer. That means, Longer has a size
+/// that is greater than or equal to the size of prefix, and each of the
+/// elements in Prefix is the same as the corresponding elements in Longer.
+///
+/// This means it also returns true when Prefix and Longer are equal!
+static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix,
+ const ArgPromotion::IndicesVector &Longer) {
+ if (Prefix.size() > Longer.size())
+ return false;
+ for (unsigned i = 0, e = Prefix.size(); i != e; ++i)
+ if (Prefix[i] != Longer[i])
+ return false;
+ return true;
+}
+
+
+/// Checks if Indices, or a prefix of Indices, is in Set.
+static bool PrefixIn(const ArgPromotion::IndicesVector &Indices,
+ std::set<ArgPromotion::IndicesVector> &Set) {
+ std::set<ArgPromotion::IndicesVector>::iterator Low;
+ Low = Set.upper_bound(Indices);
+ if (Low != Set.begin())
+ Low--;
+ // Low is now the last element smaller than or equal to Indices. This means
+ // it points to a prefix of Indices (possibly Indices itself), if such
+ // prefix exists.
+ //
+ // This load is safe if any prefix of its operands is safe to load.
+ return Low != Set.end() && IsPrefix(*Low, Indices);
+}
+
+/// Mark the given indices (ToMark) as safe in the the given set of indices
+/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
+/// is already a prefix of Indices in Safe, Indices are implicitely marked safe
+/// already. Furthermore, any indices that Indices is itself a prefix of, are
+/// removed from Safe (since they are implicitely safe because of Indices now).
+static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark,
+ std::set<ArgPromotion::IndicesVector> &Safe) {
+ std::set<ArgPromotion::IndicesVector>::iterator Low;
+ Low = Safe.upper_bound(ToMark);
+ // Guard against the case where Safe is empty
+ if (Low != Safe.begin())
+ Low--;
+ // Low is now the last element smaller than or equal to Indices. This
+ // means it points to a prefix of Indices (possibly Indices itself), if
+ // such prefix exists.
+ if (Low != Safe.end()) {
+ if (IsPrefix(*Low, ToMark))
+ // If there is already a prefix of these indices (or exactly these
+ // indices) marked a safe, don't bother adding these indices
+ return;
+
+ // Increment Low, so we can use it as a "insert before" hint
+ ++Low;
+ }
+ // Insert
+ Low = Safe.insert(Low, ToMark);
+ ++Low;
+ // If there we're a prefix of longer index list(s), remove those
+ std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end();
+ while (Low != End && IsPrefix(ToMark, *Low)) {
+ std::set<ArgPromotion::IndicesVector>::iterator Remove = Low;
+ ++Low;
+ Safe.erase(Remove);
+ }
+}
/// isSafeToPromoteArgument - As you might guess from the name of this method,
/// it checks to see if it is both safe and useful to promote the argument.
/// elements of the aggregate in order to avoid exploding the number of
/// arguments passed in.
bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const {
+ typedef std::set<IndicesVector> GEPIndicesSet;
+
+ // Quick exit for unused arguments
+ if (Arg->use_empty())
+ return true;
+
// We can only promote this argument if all of the uses are loads, or are GEP
// instructions (with constant indices) that are subsequently loaded.
+ //
+ // Promoting the argument causes it to be loaded in the caller
+ // unconditionally. This is only safe if we can prove that either the load
+ // would have happened in the callee anyway (ie, there is a load in the entry
+ // block) or the pointer passed in at every call site is guaranteed to be
+ // valid.
+ // In the former case, invalid loads can happen, but would have happened
+ // anyway, in the latter case, invalid loads won't happen. This prevents us
+ // from introducing an invalid load that wouldn't have happened in the
+ // original code.
+ //
+ // This set will contain all sets of indices that are loaded in the entry
+ // block, and thus are safe to unconditionally load in the caller.
+ GEPIndicesSet SafeToUnconditionallyLoad;
- // We can also only promote the load if we can guarantee that it will happen.
- // Promoting a load causes the load to be unconditionally executed in the
- // caller, so we can't turn a conditional load into an unconditional load in
- // general.
- bool SafeToUnconditionallyLoad = false;
- if (isByVal) // ByVal arguments are always safe to load from.
- SafeToUnconditionallyLoad = true;
+ // This set contains all the sets of indices that we are planning to promote.
+ // This makes it possible to limit the number of arguments added.
+ GEPIndicesSet ToPromote;
+ // If the pointer is always valid, any load with first index 0 is valid.
+ if(isByVal || AllCalleesPassInValidPointerForArgument(Arg))
+ SafeToUnconditionallyLoad.insert(IndicesVector(1, 0));
+
+ // First, iterate the entry block and mark loads of (geps of) arguments as
+ // safe.
BasicBlock *EntryBlock = Arg->getParent()->begin();
+ // Declare this here so we can reuse it
+ IndicesVector Indices;
+ for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end();
+ I != E; ++I)
+ if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+ Value *V = LI->getPointerOperand();
+ if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
+ V = GEP->getPointerOperand();
+ if (V == Arg) {
+ // This load actually loads (part of) Arg? Check the indices then.
+ Indices.reserve(GEP->getNumIndices());
+ for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
+ II != IE; ++II)
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(*II))
+ Indices.push_back(CI->getSExtValue());
+ else
+ // We found a non-constant GEP index for this argument? Bail out
+ // right away, can't promote this argument at all.
+ return false;
+
+ // Indices checked out, mark them as safe
+ MarkIndicesSafe(Indices, SafeToUnconditionallyLoad);
+ Indices.clear();
+ }
+ } else if (V == Arg) {
+ // Direct loads are equivalent to a GEP with a single 0 index.
+ MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad);
+ }
+ }
+
+ // Now, iterate all uses of the argument to see if there are any uses that are
+ // not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
SmallVector<LoadInst*, 16> Loads;
- std::vector<SmallVector<ConstantInt*, 8> > GEPIndices;
+ IndicesVector Operands;
for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end();
- UI != E; ++UI)
+ UI != E; ++UI) {
+ Operands.clear();
if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
if (LI->isVolatile()) return false; // Don't hack volatile loads
Loads.push_back(LI);
-
- // If this load occurs in the entry block, then the pointer is
- // unconditionally loaded.
- SafeToUnconditionallyLoad |= LI->getParent() == EntryBlock;
+ // Direct loads are equivalent to a GEP with a zero index and then a load.
+ Operands.push_back(0);
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
if (GEP->use_empty()) {
// Dead GEP's cause trouble later. Just remove them if we run into
// them.
getAnalysis<AliasAnalysis>().deleteValue(GEP);
GEP->eraseFromParent();
+ // TODO: This runs the above loop over and over again for dead GEPS
+ // Couldn't we just do increment the UI iterator earlier and erase the
+ // use?
return isSafeToPromoteArgument(Arg, isByVal);
}
+
// Ensure that all of the indices are constants.
- SmallVector<ConstantInt*, 8> Operands;
- for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
- i != e; ++i)
+ for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end();
+ i != e; ++i)
if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
- Operands.push_back(C);
+ Operands.push_back(C->getSExtValue());
else
return false; // Not a constant operand GEP!
if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
if (LI->isVolatile()) return false; // Don't hack volatile loads
Loads.push_back(LI);
-
- // If this load occurs in the entry block, then the pointer is
- // unconditionally loaded.
- SafeToUnconditionallyLoad |= LI->getParent() == EntryBlock;
} else {
+ // Other uses than load?
return false;
}
-
- // See if there is already a GEP with these indices. If not, check to
- // make sure that we aren't promoting too many elements. If so, nothing
- // to do.
- if (std::find(GEPIndices.begin(), GEPIndices.end(), Operands) ==
- GEPIndices.end()) {
- if (maxElements > 0 && GEPIndices.size() == maxElements) {
- DOUT << "argpromotion disable promoting argument '"
- << Arg->getName() << "' because it would require adding more "
- << "than " << maxElements << " arguments to the function.\n";
- // We limit aggregate promotion to only promoting up to a fixed number
- // of elements of the aggregate.
- return false;
- }
- GEPIndices.push_back(Operands);
- }
} else {
return false; // Not a load or a GEP.
}
+
+ // Now, see if it is safe to promote this load / loads of this GEP. Loading
+ // is safe if Operands, or a prefix of Operands, is marked as safe.
+ if (!PrefixIn(Operands, SafeToUnconditionallyLoad))
+ return false;
- if (Loads.empty()) return true; // No users, this is a dead argument.
+ // See if we are already promoting a load with these indices. If not, check
+ // to make sure that we aren't promoting too many elements. If so, nothing
+ // to do.
+ if (ToPromote.find(Operands) == ToPromote.end()) {
+ if (maxElements > 0 && ToPromote.size() == maxElements) {
+ DOUT << "argpromotion not promoting argument '"
+ << Arg->getName() << "' because it would require adding more "
+ << "than " << maxElements << " arguments to the function.\n";
+ // We limit aggregate promotion to only promoting up to a fixed number
+ // of elements of the aggregate.
+ return false;
+ }
+ ToPromote.insert(Operands);
+ }
+ }
- // If we decide that we want to promote this argument, the value is going to
- // be unconditionally loaded in all callees. This is only safe to do if the
- // pointer was going to be unconditionally loaded anyway (i.e. there is a load
- // of the pointer in the entry block of the function) or if we can prove that
- // all pointers passed in are always to legal locations (for example, no null
- // pointers are passed in, no pointers to free'd memory, etc).
- if (!SafeToUnconditionallyLoad &&
- !AllCalleesPassInValidPointerForArgument(Arg))
- return false; // Cannot prove that this is safe!!
+ if (Loads.empty()) return true; // No users, this is a dead argument.
// Okay, now we know that the argument is only used by load instructions and
- // it is safe to unconditionally load the pointer. Use alias analysis to
+ // it is safe to unconditionally perform all of them. Use alias analysis to
// check to see if the pointer is guaranteed to not be modified from entry of
// the function to each of the load instructions.
BasicBlock *BB = Load->getParent();
const PointerType *LoadTy =
- cast<PointerType>(Load->getOperand(0)->getType());
+ cast<PointerType>(Load->getPointerOperand()->getType());
unsigned LoadSize = (unsigned)TD.getTypeStoreSize(LoadTy->getElementType());
if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize))
return true;
}
-namespace {
- /// GEPIdxComparator - Provide a strong ordering for GEP indices. All Value*
- /// elements are instances of ConstantInt.
- ///
- struct GEPIdxComparator {
- bool operator()(const std::vector<Value*> &LHS,
- const std::vector<Value*> &RHS) const {
- unsigned idx = 0;
- for (; idx < LHS.size() && idx < RHS.size(); ++idx) {
- if (LHS[idx] != RHS[idx]) {
- return cast<ConstantInt>(LHS[idx])->getZExtValue() <
- cast<ConstantInt>(RHS[idx])->getZExtValue();
- }
- }
-
- // Return less than if we ran out of stuff in LHS and we didn't run out of
- // stuff in RHS.
- return idx == LHS.size() && idx != RHS.size();
- }
- };
-}
-
-
/// DoPromotion - This method actually performs the promotion of the specified
/// arguments, and returns the new function. At this point, we know that it's
/// safe to do so.
const FunctionType *FTy = F->getFunctionType();
std::vector<const Type*> Params;
- typedef std::set<std::vector<Value*>, GEPIdxComparator> ScalarizeTable;
+ typedef std::set<IndicesVector> ScalarizeTable;
// ScalarizedElements - If we are promoting a pointer that has elements
// accessed out of it, keep track of which elements are accessed so that we
// OriginalLoads - Keep track of a representative load instruction from the
// original function so that we can tell the alias analysis implementation
// what the new GEP/Load instructions we are inserting look like.
- std::map<std::vector<Value*>, LoadInst*> OriginalLoads;
+ std::map<IndicesVector, LoadInst*> OriginalLoads;
// ParamAttrs - Keep track of the parameter attributes for the arguments
// that we are *not* promoting. For the ones that we do promote, the parameter
// Add any return attributes.
if (ParameterAttributes attrs = PAL.getParamAttrs(0))
ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, attrs));
-
+
+ // First, determine the new argument list
unsigned ArgIndex = 1;
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
++I, ++ArgIndex) {
if (ByValArgsToTransform.count(I)) {
- // Just add all the struct element types.
+ // Simple byval argument? Just add all the struct element types.
const Type *AgTy = cast<PointerType>(I->getType())->getElementType();
const StructType *STy = cast<StructType>(AgTy);
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
Params.push_back(STy->getElementType(i));
++NumByValArgsPromoted;
} else if (!ArgsToPromote.count(I)) {
+ // Unchanged argument
Params.push_back(I->getType());
if (ParameterAttributes attrs = PAL.getParamAttrs(ArgIndex))
ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), attrs));
} else if (I->use_empty()) {
+ // Dead argument (which are always marked as promotable)
++NumArgumentsDead;
} else {
- // Okay, this is being promoted. Check to see if there are any GEP uses
- // of the argument.
+ // Okay, this is being promoted. This means that the only uses are loads
+ // or GEPs which are only used by loads
+
+ // In this table, we will track which indices are loaded from the argument
+ // (where direct loads are tracked as no indices).
ScalarizeTable &ArgIndices = ScalarizedElements[I];
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
++UI) {
Instruction *User = cast<Instruction>(*UI);
assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User));
- std::vector<Value*> Indices(User->op_begin()+1, User->op_end());
+ IndicesVector Indices;
+ Indices.reserve(User->getNumOperands() - 1);
+ // Since loads will only have a single operand, and GEPs only a single
+ // non-index operand, this will record direct loads without any indices,
+ // and gep+loads with the GEP indices.
+ for (User::op_iterator II = User->op_begin() + 1, IE = User->op_end();
+ II != IE; ++II)
+ Indices.push_back(cast<ConstantInt>(*II)->getSExtValue());
+ // GEPs with a single 0 index can be merged with direct loads
+ if (Indices.size() == 1 && Indices.front() == 0)
+ Indices.clear();
ArgIndices.insert(Indices);
LoadInst *OrigLoad;
if (LoadInst *L = dyn_cast<LoadInst>(User))
OrigLoad = L;
else
+ // Take any load, we will use it only to update Alias Analysis
OrigLoad = cast<LoadInst>(User->use_back());
OriginalLoads[Indices] = OrigLoad;
}
// Add a parameter to the function for each element passed in.
for (ScalarizeTable::iterator SI = ArgIndices.begin(),
- E = ArgIndices.end(); SI != E; ++SI)
+ E = ArgIndices.end(); SI != E; ++SI) {
Params.push_back(GetElementPtrInst::getIndexedType(I->getType(),
- SI->begin(),
- SI->end()));
+ &*SI->begin(),
+ SI->size()));
+ assert(Params.back());
+ }
if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
++NumArgumentsPromoted;
} else if (!I->use_empty()) {
// Non-dead argument: insert GEPs and loads as appropriate.
ScalarizeTable &ArgIndices = ScalarizedElements[I];
+ // Store the Value* version of the indices in here, but declare it now
+ // for reuse
+ std::vector<Value*> Ops;
for (ScalarizeTable::iterator SI = ArgIndices.begin(),
E = ArgIndices.end(); SI != E; ++SI) {
Value *V = *AI;
LoadInst *OrigLoad = OriginalLoads[*SI];
if (!SI->empty()) {
- V = GetElementPtrInst::Create(V, SI->begin(), SI->end(),
+ Ops.reserve(SI->size());
+ const Type *ElTy = V->getType();
+ for (IndicesVector::const_iterator II = SI->begin(),
+ IE = SI->end(); II != IE; ++II) {
+ // Use i32 to index structs, and i64 for others (pointers/arrays).
+ // This satisfies GEP constraints.
+ const Type *IdxTy = (isa<StructType>(ElTy) ? Type::Int32Ty : Type::Int64Ty);
+ Ops.push_back(ConstantInt::get(IdxTy, *II));
+ // Keep track of the type we're currently indexing
+ ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II);
+ }
+ // And create a GEP to extract those indices
+ V = GetElementPtrInst::Create(V, Ops.begin(), Ops.end(),
V->getName()+".idx", Call);
+ Ops.clear();
AA.copyValue(OrigLoad->getOperand(0), V);
}
Args.push_back(new LoadInst(V, V->getName()+".val", Call));
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
Idxs[1] = ConstantInt::get(Type::Int32Ty, i);
+ std::string Name = TheAlloca->getName()+"."+utostr(i);
Value *Idx = GetElementPtrInst::Create(TheAlloca, Idxs, Idxs+2,
- TheAlloca->getName()+"."+utostr(i),
- InsertPt);
+ Name, InsertPt);
I2->setName(I->getName()+"."+utostr(i));
new StoreInst(I2++, Idx, InsertPt);
}
}
// Otherwise, if we promoted this argument, then all users are load
- // instructions, and all loads should be using the new argument that we
- // added.
+ // instructions (or GEPs with only load users), and all loads should be
+ // using the new argument that we added.
ScalarizeTable &ArgIndices = ScalarizedElements[I];
while (!I->use_empty()) {
<< "' in function '" << F->getName() << "'\n";
} else {
GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back());
- std::vector<Value*> Operands(GEP->op_begin()+1, GEP->op_end());
+ IndicesVector Operands;
+ Operands.reserve(GEP->getNumIndices());
+ for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
+ II != IE; ++II)
+ Operands.push_back(cast<ConstantInt>(*II)->getSExtValue());
+
+ // GEPs with a single 0 index can be merged with direct loads
+ if (Operands.size() == 1 && Operands.front() == 0)
+ Operands.clear();
Function::arg_iterator TheArg = I2;
for (ScalarizeTable::iterator It = ArgIndices.begin();
}
std::string NewName = I->getName();
- for (unsigned i = 0, e = Operands.size(); i != e; ++i)
- if (ConstantInt *CI = dyn_cast<ConstantInt>(Operands[i]))
- NewName += "." + CI->getValue().toStringUnsigned(10);
- else
- NewName += ".x";
- TheArg->setName(NewName+".val");
+ for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
+ NewName += "." + utostr(Operands[i]);
+ }
+ NewName += ".val";
+ TheArg->setName(NewName);
DOUT << "*** Promoted agg argument '" << TheArg->getName()
- << "' of function '" << F->getName() << "'\n";
+ << "' of function '" << NF->getName() << "'\n";
// All of the uses must be load instructions. Replace them all with
// the argument specified by ArgNo.