//===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
-//
+//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+//
//===----------------------------------------------------------------------===//
//
// This pass promotes "by reference" arguments to be "by value" arguments. In
// practice, this means looking for internal functions that have pointer
-// arguments. If we can prove, through the use of alias analysis, that that an
-// argument is *only* loaded, then we can pass the value into the function
+// arguments. If it can prove, through the use of alias analysis, that an
+// argument is *only* loaded, then it can pass the value into the function
// instead of the address of the value. This can cause recursive simplification
// of code and lead to the elimination of allocas (especially in C++ template
// code like the STL).
//
// 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
-// we refuse to scalarize aggregates which would require passing in more than
-// three operands to the function, because we don't want to pass thousands of
-// operands for a large array or structure!
+// 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!
//
// Note that this transformation could also be done for arguments that are only
-// stored to (returning the value instead), but we do not currently handle that
-// case. This case would be best handled when and if we start supporting
-// multiple return values from functions.
+// stored to (returning the value instead), but does not currently. This case
+// would be best handled when and if LLVM begins supporting multiple return
+// values from functions.
//
//===----------------------------------------------------------------------===//
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Module.h"
-#include "llvm/Pass.h"
+#include "llvm/CallGraphSCCPass.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/CallGraph.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/CFG.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/Compiler.h"
#include <set>
using namespace llvm;
-namespace {
- Statistic<> NumArgumentsPromoted("argpromotion",
- "Number of pointer arguments promoted");
- Statistic<> NumAggregatesPromoted("argpromotion",
- "Number of aggregate arguments promoted");
- Statistic<> NumArgumentsDead("argpromotion",
- "Number of dead pointer args eliminated");
+STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted");
+STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
+STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated");
+namespace {
/// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
///
- class ArgPromotion : public Pass {
- // WorkList - The set of internal functions that we have yet to process. As
- // we eliminate arguments from a function, we push all callers into this set
- // so that the by-reference argument can be bubbled out as far as possible.
- // This set contains only internal functions.
- std::set<Function*> WorkList;
- public:
+ struct VISIBILITY_HIDDEN ArgPromotion : public CallGraphSCCPass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<AliasAnalysis>();
AU.addRequired<TargetData>();
+ CallGraphSCCPass::getAnalysisUsage(AU);
}
- virtual bool run(Module &M);
+ virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
+ static char ID; // Pass identification, replacement for typeid
+ ArgPromotion() : CallGraphSCCPass((intptr_t)&ID) {}
+
private:
- bool PromoteArguments(Function *F);
- bool isSafeToPromoteArgument(Argument *Arg) const;
-
void DoPromotion(Function *F, std::vector<Argument*> &ArgsToPromote);
+ bool PromoteArguments(CallGraphNode *CGN);
+ bool isSafeToPromoteArgument(Argument *Arg) const;
+
Function *DoPromotion(Function *F, std::vector<Argument*> &ArgsToPromote);
};
- RegisterOpt<ArgPromotion> X("argpromotion",
- "Promote 'by reference' arguments to scalars");
+ char ArgPromotion::ID = 0;
+ RegisterPass<ArgPromotion> X("argpromotion",
+ "Promote 'by reference' arguments to scalars");
}
Pass *llvm::createArgumentPromotionPass() {
return new ArgPromotion();
}
-bool ArgPromotion::run(Module &M) {
- bool Changed = false;
- for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
- if (I->hasInternalLinkage())
- WorkList.insert(I);
-
- while (!WorkList.empty()) {
- Function *F = *WorkList.begin();
- WorkList.erase(WorkList.begin());
-
- if (PromoteArguments(F)) // Attempt to promote an argument.
- Changed = true; // Remember that we changed something.
- }
-
+bool ArgPromotion::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
+ bool Changed = false, LocalChange;
+
+ do { // Iterate until we stop promoting from this SCC.
+ LocalChange = false;
+ // Attempt to promote arguments from all functions in this SCC.
+ for (unsigned i = 0, e = SCC.size(); i != e; ++i)
+ LocalChange |= PromoteArguments(SCC[i]);
+ Changed |= LocalChange; // Remember that we changed something.
+ } while (LocalChange);
+
return Changed;
}
/// example, all callers are direct). If safe to promote some arguments, it
/// calls the DoPromotion method.
///
-bool ArgPromotion::PromoteArguments(Function *F) {
- assert(F->hasInternalLinkage() && "We can only process internal functions!");
+bool ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
+ Function *F = CGN->getFunction();
+
+ // Make sure that it is local to this module.
+ if (!F || !F->hasInternalLinkage()) return false;
// First check: see if there are any pointer arguments! If not, quick exit.
std::vector<Argument*> PointerArgs;
- for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
+ for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
if (isa<PointerType>(I->getType()))
PointerArgs.push_back(I);
if (PointerArgs.empty()) return false;
if (PointerArgs.empty()) return false;
// Okay, promote all of the arguments are rewrite the callees!
- DoPromotion(F, PointerArgs);
+ Function *NewF = DoPromotion(F, PointerArgs);
+
+ // Update the call graph to know that the old function is gone.
+ getAnalysis<CallGraph>().changeFunction(F, NewF);
+ return true;
+}
+
+/// IsAlwaysValidPointer - Return true if the specified pointer is always legal
+/// to load.
+static bool IsAlwaysValidPointer(Value *V) {
+ if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true;
+ if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V))
+ return IsAlwaysValidPointer(GEP->getOperand(0));
+ if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
+ if (CE->getOpcode() == Instruction::GetElementPtr)
+ return IsAlwaysValidPointer(CE->getOperand(0));
+
+ return false;
+}
+
+/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that
+/// all callees pass in a valid pointer for the specified function argument.
+static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) {
+ Function *Callee = Arg->getParent();
+
+ unsigned ArgNo = std::distance(Callee->arg_begin(),
+ Function::arg_iterator(Arg));
+
+ // Look at all call sites of the function. At this pointer we know we only
+ // have direct callees.
+ for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end();
+ UI != E; ++UI) {
+ CallSite CS = CallSite::get(*UI);
+ assert(CS.getInstruction() && "Should only have direct calls!");
+
+ if (!IsAlwaysValidPointer(CS.getArgument(ArgNo)))
+ return false;
+ }
return true;
}
bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
// We can only promote this argument if all of the uses are loads, or are GEP
// instructions (with constant indices) that are subsequently loaded.
+ bool HasLoadInEntryBlock = false;
+ BasicBlock *EntryBlock = Arg->getParent()->begin();
std::vector<LoadInst*> Loads;
std::vector<std::vector<ConstantInt*> > GEPIndices;
for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end();
if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
if (LI->isVolatile()) return false; // Don't hack volatile loads
Loads.push_back(LI);
+ HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
} 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
if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
if (LI->isVolatile()) return false; // Don't hack volatile loads
Loads.push_back(LI);
+ HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
} else {
return false;
}
if (std::find(GEPIndices.begin(), GEPIndices.end(), Operands) ==
GEPIndices.end()) {
if (GEPIndices.size() == 3) {
- DEBUG(std::cerr << "argpromotion disable promoting argument '"
- << Arg->getName() << "' because it would require adding more "
- << "than 3 arguments to the function.\n");
+ DOUT << "argpromotion disable promoting argument '"
+ << Arg->getName() << "' because it would require adding more "
+ << "than 3 arguments to the function.\n";
// We limit aggregate promotion to only promoting up to three elements
// of the aggregate.
return false;
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. 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.
- Function &F = *Arg->getParent();
+ // 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 (!HasLoadInEntryBlock && !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
+ // check to see if the pointer is guaranteed to not be modified from entry of
+ // the function to each of the load instructions.
// Because there could be several/many load instructions, remember which
// blocks we know to be transparent to the load.
const PointerType *LoadTy =
cast<PointerType>(Load->getOperand(0)->getType());
- unsigned LoadSize = TD.getTypeSize(LoadTy->getElementType());
+ unsigned LoadSize = (unsigned)TD.getTypeStoreSize(LoadTy->getElementType());
if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize))
return false; // Pointer is invalidated!
unsigned idx = 0;
for (; idx < LHS.size() && idx < RHS.size(); ++idx) {
if (LHS[idx] != RHS[idx]) {
- return cast<ConstantInt>(LHS[idx])->getRawValue() <
- cast<ConstantInt>(RHS[idx])->getRawValue();
+ return cast<ConstantInt>(LHS[idx])->getZExtValue() <
+ cast<ConstantInt>(RHS[idx])->getZExtValue();
}
}
/// DoPromotion - This method actually performs the promotion of the specified
-/// arguments. At this point, we know that it's safe to do so.
-void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
+/// arguments, and returns the new function. At this point, we know that it's
+/// safe to do so.
+Function *ArgPromotion::DoPromotion(Function *F,
+ std::vector<Argument*> &Args2Prom) {
std::set<Argument*> ArgsToPromote(Args2Prom.begin(), Args2Prom.end());
-
+
// Start by computing a new prototype for the function, which is the same as
// the old function, but has modified arguments.
const FunctionType *FTy = F->getFunctionType();
// what the new GEP/Load instructions we are inserting look like.
std::map<std::vector<Value*>, LoadInst*> OriginalLoads;
- for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
+ for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
if (!ArgsToPromote.count(I)) {
Params.push_back(I->getType());
} else if (I->use_empty()) {
// Add a parameter to the function for each element passed in.
for (ScalarizeTable::iterator SI = ArgIndices.begin(),
E = ArgIndices.end(); SI != E; ++SI)
- Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI));
+ Params.push_back(GetElementPtrInst::getIndexedType(I->getType(),
+ SI->begin(),
+ SI->end()));
if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
++NumArgumentsPromoted;
bool ExtraArgHack = false;
if (Params.empty() && FTy->isVarArg()) {
ExtraArgHack = true;
- Params.push_back(Type::IntTy);
+ Params.push_back(Type::Int32Ty);
}
FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
-
+
// Create the new function body and insert it into the module...
Function *NF = new Function(NFTy, F->getLinkage(), F->getName());
+ NF->setCallingConv(F->getCallingConv());
F->getParent()->getFunctionList().insert(F, NF);
// Get the alias analysis information that we need to update to reflect our
CallSite CS = CallSite::get(F->use_back());
Instruction *Call = CS.getInstruction();
- // Make sure the caller of this function is revisited now that we promoted
- // arguments in a callee of it.
- if (Call->getParent()->getParent()->hasInternalLinkage())
- WorkList.insert(Call->getParent()->getParent());
-
// Loop over the operands, inserting GEP and loads in the caller as
// appropriate.
CallSite::arg_iterator AI = CS.arg_begin();
- for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I, ++AI)
+ for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
+ I != E; ++I, ++AI)
if (!ArgsToPromote.count(I))
Args.push_back(*AI); // Unmodified argument
else if (!I->use_empty()) {
Value *V = *AI;
LoadInst *OrigLoad = OriginalLoads[*SI];
if (!SI->empty()) {
- V = new GetElementPtrInst(V, *SI, V->getName()+".idx", Call);
+ V = new GetElementPtrInst(V, SI->begin(), SI->end(),
+ V->getName()+".idx", Call);
AA.copyValue(OrigLoad->getOperand(0), V);
}
Args.push_back(new LoadInst(V, V->getName()+".val", Call));
}
if (ExtraArgHack)
- Args.push_back(Constant::getNullValue(Type::IntTy));
+ Args.push_back(Constant::getNullValue(Type::Int32Ty));
// Push any varargs arguments on the list
for (; AI != CS.arg_end(); ++AI)
Instruction *New;
if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
- Args, "", Call);
+ Args.begin(), Args.end(), "", Call);
+ cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
} else {
- New = new CallInst(NF, Args, "", Call);
+ New = new CallInst(NF, Args.begin(), Args.end(), "", Call);
+ cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
+ if (cast<CallInst>(Call)->isTailCall())
+ cast<CallInst>(New)->setTailCall();
}
Args.clear();
if (!Call->use_empty()) {
Call->replaceAllUsesWith(New);
- std::string Name = Call->getName();
- Call->setName("");
- New->setName(Name);
+ New->takeName(Call);
}
-
+
// Finally, remove the old call from the program, reducing the use-count of
// F.
Call->getParent()->getInstList().erase(Call);
// Loop over the argument list, transfering uses of the old arguments over to
// the new arguments, also transfering over the names as well.
//
- for (Function::aiterator I = F->abegin(), E = F->aend(), I2 = NF->abegin();
- I != E; ++I)
+ for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
+ I2 = NF->arg_begin(); I != E; ++I)
if (!ArgsToPromote.count(I)) {
// If this is an unmodified argument, move the name and users over to the
// new version.
I->replaceAllUsesWith(I2);
- I2->setName(I->getName());
+ I2->takeName(I);
AA.replaceWithNewValue(I, I2);
++I2;
} else if (I->use_empty()) {
LI->replaceAllUsesWith(I2);
AA.replaceWithNewValue(LI, I2);
LI->getParent()->getInstList().erase(LI);
- DEBUG(std::cerr << "*** Promoted load of argument '" << I->getName()
- << "' in function '" << F->getName() << "'\n");
+ DOUT << "*** Promoted load of argument '" << I->getName()
+ << "' in function '" << F->getName() << "'\n";
} else {
GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back());
std::vector<Value*> Operands(GEP->op_begin()+1, GEP->op_end());
- unsigned ArgNo = 0;
- Function::aiterator TheArg = I2;
+ Function::arg_iterator TheArg = I2;
for (ScalarizeTable::iterator It = ArgIndices.begin();
*It != Operands; ++It, ++TheArg) {
assert(It != ArgIndices.end() && "GEP not handled??");
std::string NewName = I->getName();
for (unsigned i = 0, e = Operands.size(); i != e; ++i)
if (ConstantInt *CI = dyn_cast<ConstantInt>(Operands[i]))
- NewName += "."+itostr((int64_t)CI->getRawValue());
+ NewName += "." + CI->getValue().toStringUnsigned(10);
else
NewName += ".x";
TheArg->setName(NewName+".val");
- DEBUG(std::cerr << "*** Promoted agg argument '" << TheArg->getName()
- << "' of function '" << F->getName() << "'\n");
+ DOUT << "*** Promoted agg argument '" << TheArg->getName()
+ << "' of function '" << F->getName() << "'\n";
// All of the uses must be load instructions. Replace them all with
// the argument specified by ArgNo.
}
}
- // If we inserted a new pointer type, it's possible that IT could be
- // promoted too. Also, increment I2 past all of the arguments added for
- // this promoted pointer.
- for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i, ++I2)
- if (isa<PointerType>(I2->getType()))
- WorkList.insert(NF);
+ // Increment I2 past all of the arguments added for this promoted pointer.
+ for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i)
+ ++I2;
}
// Notify the alias analysis implementation that we inserted a new argument.
if (ExtraArgHack)
- AA.copyValue(Constant::getNullValue(Type::IntTy), NF->abegin());
+ AA.copyValue(Constant::getNullValue(Type::Int32Ty), NF->arg_begin());
// Tell the alias analysis that the old function is about to disappear.
// Now that the old function is dead, delete it.
F->getParent()->getFunctionList().erase(F);
+ return NF;
}
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