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Fairly substantial changes to update the alias analysis we are querying as

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we make the transformation.  This allows us to use interprocedural alias
analyses successfully.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13691 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-05-23 21:21:17 +00:00
parent 2741c97104
commit 9e7cc2f0d4
1 changed files with 92 additions and 39 deletions
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131
lib/Transforms/IPO/ArgumentPromotion.cpp
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@ -1,4 +1,4 @@
//===-- ArgumentPromotion.cpp - Promote 'by reference' arguments ----------===//
//===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
//
// The LLVM Compiler Infrastructure
//
@ -12,14 +12,14 @@
// 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
// 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.
// 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 something!
// operands for a large array or structure!
//
// 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
@ -28,6 +28,7 @@
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "argpromotion"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
@ -58,7 +59,7 @@ namespace {
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.
// 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:
@ -128,7 +129,11 @@ bool ArgPromotion::run(Module &M) {
return Changed;
}
/// PromoteArguments - This method checks the specified function to see if there
/// are any promotable arguments and if it is safe to promote the function (for
/// 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!");
@ -144,15 +149,14 @@ bool ArgPromotion::PromoteArguments(Function *F) {
for (Value::use_iterator UI = F->use_begin(), E = F->use_end();
UI != E; ++UI) {
CallSite CS = CallSite::get(*UI);
if (Instruction *I = CS.getInstruction()) {
// Ensure that this call site is CALLING the function, not passing it as
// an argument.
for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
AI != E; ++AI)
if (*AI == F) return false; // Passing the function address in!
} else {
return false; // Cannot promote an indirect call!
}
if (!CS.getInstruction()) // "Taking the address" of the function
return false;
// Ensure that this call site is CALLING the function, not passing it as
// an argument.
for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
AI != E; ++AI)
if (*AI == F) return false; // Passing the function address in!
}
// Check to see which arguments are promotable. If an argument is not
@ -171,6 +175,12 @@ bool ArgPromotion::PromoteArguments(Function *F) {
return true;
}
/// 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.
/// This method limits promotion of aggregates to only promote up to three
/// elements of the aggregate in order to avoid exploding the number of
/// arguments passed in.
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.
@ -185,6 +195,7 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
if (GEP->use_empty()) {
// Dead GEP's cause trouble later. Just remove them if we run into
// them.
getAnalysis<AliasAnalysis>().deleteValue(GEP);
GEP->getParent()->getInstList().erase(GEP);
return isSafeToPromoteArgument(Arg);
}
@ -206,12 +217,15 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
return false;
}
// See if there is already a GEP with these indices. If so, check to make
// sure that we aren't promoting too many elements. If not, nothing to
// do.
// 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 (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");
// We limit aggregate promotion to only promoting up to three elements
// of the aggregate.
return false;
@ -222,11 +236,11 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
return false; // Not a load or a GEP.
}
if (Loads.empty()) return true; // No users, dead argument.
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.
// Check to see if the pointer is guaranteed to not be modified from entry of
// the function to each of the load instructions.
// 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();
// Because there could be several/many load instructions, remember which
@ -265,7 +279,8 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
return true;
}
/// 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) {
std::set<Argument*> ArgsToPromote(Args2Prom.begin(), Args2Prom.end());
@ -283,10 +298,17 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
//
std::map<Argument*, std::set<std::vector<Value*> > > ScalarizedElements;
// 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;
for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
if (!ArgsToPromote.count(I)) {
Params.push_back(I->getType());
} else if (!I->use_empty()) {
} else if (I->use_empty()) {
++NumArgumentsDead;
} else {
// Okay, this is being promoted. Check to see if there are any GEP uses
// of the argument.
std::set<std::vector<Value*> > &ArgIndices = ScalarizedElements[I];
@ -294,8 +316,14 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
++UI) {
Instruction *User = cast<Instruction>(*UI);
assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User));
ArgIndices.insert(std::vector<Value*>(User->op_begin()+1,
User->op_end()));
std::vector<Value*> Indices(User->op_begin()+1, User->op_end());
ArgIndices.insert(Indices);
LoadInst *OrigLoad;
if (LoadInst *L = dyn_cast<LoadInst>(User))
OrigLoad = L;
else
OrigLoad = cast<LoadInst>(User->use_back());
OriginalLoads[Indices] = OrigLoad;
}
// Add a parameter to the function for each element passed in.
@ -307,8 +335,6 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
++NumArgumentsPromoted;
else
++NumAggregatesPromoted;
} else {
++NumArgumentsDead;
}
const Type *RetTy = FTy->getReturnType();
@ -325,7 +351,11 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
// Create the new function body and insert it into the module...
Function *NF = new Function(NFTy, F->getLinkage(), F->getName());
F->getParent()->getFunctionList().insert(F, NF);
// Get the alias analysis information that we need to update to reflect our
// changes.
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
// Loop over all of the callers of the function, transforming the call sites
// to pass in the loaded pointers.
//
@ -334,25 +364,30 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
CallSite CS = CallSite::get(F->use_back());
Instruction *Call = CS.getInstruction();
// Make sure the caller of this function is revisited.
// 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, deleting dead ones...
// 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)
if (!ArgsToPromote.count(I))
Args.push_back(*AI); // Unmodified argument
else if (!I->use_empty()) {
// Non-dead argument.
// Non-dead argument: insert GEPs and loads as appropriate.
std::set<std::vector<Value*> > &ArgIndices = ScalarizedElements[I];
for (std::set<std::vector<Value*> >::iterator SI = ArgIndices.begin(),
E = ArgIndices.end(); SI != E; ++SI) {
Value *V = *AI;
if (!SI->empty())
LoadInst *OrigLoad = OriginalLoads[*SI];
if (!SI->empty()) {
V = new GetElementPtrInst(V, *SI, V->getName()+".idx", Call);
AA.copyValue(OrigLoad->getOperand(0), V);
}
Args.push_back(new LoadInst(V, V->getName()+".val", Call));
AA.copyValue(OrigLoad, Args.back());
}
}
@ -372,6 +407,10 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
}
Args.clear();
// Update the alias analysis implementation to know that we are replacing
// the old call with a new one.
AA.replaceWithNewValue(Call, New);
if (!Call->use_empty()) {
Call->replaceAllUsesWith(New);
std::string Name = Call->getName();
@ -399,8 +438,11 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
// new version.
I->replaceAllUsesWith(I2);
I2->setName(I->getName());
AA.replaceWithNewValue(I, I2);
++I2;
} else if (!I->use_empty()) {
} else if (I->use_empty()) {
AA.deleteValue(I);
} else {
// Otherwise, if we promoted this argument, then all users are load
// instructions, and all loads should be using the new argument that we
// added.
@ -412,9 +454,10 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
"Load element should sort to front!");
I2->setName(I->getName()+".val");
LI->replaceAllUsesWith(I2);
AA.replaceWithNewValue(LI, I2);
LI->getParent()->getInstList().erase(LI);
DEBUG(std::cerr << "*** Promoted argument '" << I->getName()
<< "' of function '" << F->getName() << "'\n");
DEBUG(std::cerr << "*** 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());
@ -442,20 +485,30 @@ void ArgPromotion::DoPromotion(Function *F, std::vector<Argument*> &Args2Prom) {
while (!GEP->use_empty()) {
LoadInst *L = cast<LoadInst>(GEP->use_back());
L->replaceAllUsesWith(TheArg);
AA.replaceWithNewValue(L, TheArg);
L->getParent()->getInstList().erase(L);
}
AA.deleteValue(GEP);
GEP->getParent()->getInstList().erase(GEP);
}
}
// If we inserted a new pointer type, it's possible that IT could be
// promoted too. Also, increment I2 past all of the arguments for this
// pointer.
// 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);
}
// Notify the alias analysis implementation that we inserted a new argument.
if (ExtraArgHack)
AA.copyValue(Constant::getNullValue(Type::IntTy), NF->abegin());
// Tell the alias analysis that the old function is about to disappear.
AA.replaceWithNewValue(F, NF);
// Now that the old function is dead, delete it.
F->getParent()->getFunctionList().erase(F);
}