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Restructure ArgumentPromotion a bit. Instead of just having a single boolean 

that says "unconditional loads from this argument are safe", we now keep track
of the safety per set of indices from which loads happen. This prevents
ArgPromotion from promoting loads that aren't really valid. As an added effect,
this will now disregard the the type of the indices passed to a GEP, so
"load GEP %A, i32 1" and "load GEP %A, i64 1" will result in a single argument,
not two.

This fixes PR2598, for which a testcase has been added as well.

llvm-svn: 54159
This commit is contained in:
Matthijs Kooijman 2008-07-29 10:00:13 +00:00
parent 3d5d6f90e0
commit fd3070459b
2 changed files with 260 additions and 99 deletions
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334
llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
View File

@ -17,10 +17,10 @@
//
// 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
@ -68,6 +68,9 @@ namespace {
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);
@ -222,6 +225,72 @@ static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) {
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.
@ -229,43 +298,99 @@ static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) {
/// 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!
@ -275,47 +400,39 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const {
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;
// 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 (Loads.empty()) return true; // No users, this is a dead argument.
// 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!!
// 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.
@ -333,7 +450,7 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const {
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))
@ -356,29 +473,6 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const {
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.
@ -391,7 +485,7 @@ Function *ArgPromotion::DoPromotion(Function *F,
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
@ -405,7 +499,7 @@ Function *ArgPromotion::DoPromotion(Function *F,
// 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
@ -416,47 +510,66 @@ Function *ArgPromotion::DoPromotion(Function *F,
// 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;
@ -535,13 +648,29 @@ Function *ArgPromotion::DoPromotion(Function *F,
} 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));
@ -624,9 +753,9 @@ Function *ArgPromotion::DoPromotion(Function *F,
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);
}
@ -644,8 +773,8 @@ Function *ArgPromotion::DoPromotion(Function *F,
}
// 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()) {
@ -660,7 +789,15 @@ Function *ArgPromotion::DoPromotion(Function *F,
<< "' 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();
@ -669,15 +806,14 @@ Function *ArgPromotion::DoPromotion(Function *F,
}
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.

25
llvm/test/Transforms/ArgumentPromotion/2008-07-02-array-indexing.ll Normal file
View File

@ -0,0 +1,25 @@
; RUN: llvm-as < %s | opt -argpromotion | llvm-dis > %t
; RUN: cat %t | grep {define.*@callee(.*i32\\*}
; PR2498
; This test tries to convince argpromotion about promoting the load from %A + 2,
; because there is a load of %A in the entry block
define internal i32 @callee(i1 %C, i32* %A) {
entry:
; Unconditonally load the element at %A
%A.0 = load i32* %A
br i1 %C, label %T, label %F
T:
ret i32 %A.0
F:
; Load the element at offset two from %A. This should not be promoted!
%A.2 = getelementptr i32* %A, i32 2
%R = load i32* %A.2
ret i32 %R
}
define i32 @foo() {
%X = call i32 @callee(i1 false, i32* null) ; <i32> [#uses=1]
ret i32 %X
}