llvm-6502/lib/Transforms/IPO/DeadArgumentElimination.cpp
Misha Brukman 7bc439a4b6 Spell `definitely' correctly.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@8466 91177308-0d34-0410-b5e6-96231b3b80d8
2003-09-11 15:31:17 +00:00

324 lines
13 KiB
C++

//===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===//
//
// This pass deletes dead arguments from internal functions. Dead argument
// elimination removes arguments which are directly dead, as well as arguments
// only passed into function calls as dead arguments of other functions.
//
// This pass is often useful as a cleanup pass to run after aggressive
// interprocedural passes, which add possibly-dead arguments.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Constant.h"
#include "llvm/iOther.h"
#include "llvm/iTerminators.h"
#include "llvm/Support/CallSite.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
#include "Support/iterator"
#include <set>
namespace {
Statistic<> NumArgumentsEliminated("deadargelim", "Number of args removed");
struct DAE : public Pass {
DAE(bool DFEF = false) : DeleteFromExternalFunctions(DFEF) {}
bool run(Module &M);
private:
bool DeleteFromExternalFunctions;
bool FunctionArgumentsIntrinsicallyAlive(const Function &F);
void RemoveDeadArgumentsFromFunction(Function *F,
std::set<Argument*> &DeadArguments);
};
RegisterOpt<DAE> X("deadargelim", "Dead Argument Elimination");
}
/// createDeadArgEliminationPass - This pass removes arguments from functions
/// which are not used by the body of the function. If
/// DeleteFromExternalFunctions is true, the pass will modify functions that
/// have external linkage, which is not usually safe (this is used by bugpoint
/// to reduce testcases).
///
Pass *createDeadArgEliminationPass(bool DeleteFromExternalFunctions) {
return new DAE(DeleteFromExternalFunctions);
}
// FunctionArgumentsIntrinsicallyAlive - Return true if the arguments of the
// specified function are intrinsically alive.
//
// We consider arguments of non-internal functions to be intrinsically alive as
// well as arguments to functions which have their "address taken".
//
bool DAE::FunctionArgumentsIntrinsicallyAlive(const Function &F) {
if (!F.hasInternalLinkage() && !DeleteFromExternalFunctions) return true;
for (Value::use_const_iterator I = F.use_begin(), E = F.use_end(); I!=E; ++I){
// If this use is anything other than a call site, the function is alive.
CallSite CS = CallSite::get(const_cast<User*>(*I));
if (!CS.getInstruction()) return true; // Not a valid call site?
// If the function is PASSED IN as an argument, its address has been taken
for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end(); AI != E;
++AI)
if (AI->get() == &F) return true;
}
return false;
}
namespace {
enum ArgumentLiveness { Alive, MaybeLive, Dead };
}
// getArgumentLiveness - Inspect an argument, determining if is known Alive
// (used in a computation), MaybeLive (only passed as an argument to a call), or
// Dead (not used).
static ArgumentLiveness getArgumentLiveness(const Argument &A) {
if (A.use_empty()) return Dead; // First check, directly dead?
// Scan through all of the uses, looking for non-argument passing uses.
for (Value::use_const_iterator I = A.use_begin(), E = A.use_end(); I!=E;++I) {
CallSite CS = CallSite::get(const_cast<User*>(*I));
if (!CS.getInstruction()) {
// If its used by something that is not a call or invoke, it's alive!
return Alive;
}
// If it's an indirect call, mark it alive...
Function *Callee = CS.getCalledFunction();
if (!Callee) return Alive;
// Check to see if it's passed through a va_arg area: if so, we cannot
// remove it.
unsigned NumFixedArgs = Callee->getFunctionType()->getNumParams();
for (CallSite::arg_iterator AI = CS.arg_begin()+NumFixedArgs;
AI != CS.arg_end(); ++AI)
if (AI->get() == &A) // If passed through va_arg area, we cannot remove it
return Alive;
}
return MaybeLive; // It must be used, but only as argument to a function
}
// isMaybeLiveArgumentNowAlive - Check to see if Arg is alive. At this point,
// we know that the only uses of Arg are to be passed in as an argument to a
// function call. Check to see if the formal argument passed in is in the
// LiveArguments set. If so, return true.
//
static bool isMaybeLiveArgumentNowAlive(Argument *Arg,
const std::set<Argument*> &LiveArguments) {
for (Value::use_iterator I = Arg->use_begin(), E = Arg->use_end(); I!=E; ++I){
CallSite CS = CallSite::get(*I);
// We know that this can only be used for direct calls...
Function *Callee = cast<Function>(CS.getCalledValue());
// Loop over all of the arguments (because Arg may be passed into the call
// multiple times) and check to see if any are now alive...
CallSite::arg_iterator CSAI = CS.arg_begin();
for (Function::aiterator AI = Callee->abegin(), E = Callee->aend();
AI != E; ++AI, ++CSAI)
// If this is the argument we are looking for, check to see if it's alive
if (*CSAI == Arg && LiveArguments.count(AI))
return true;
}
return false;
}
// MarkArgumentLive - The MaybeLive argument 'Arg' is now known to be alive.
// Mark it live in the specified sets and recursively mark arguments in callers
// live that are needed to pass in a value.
//
static void MarkArgumentLive(Argument *Arg,
std::set<Argument*> &MaybeLiveArguments,
std::set<Argument*> &LiveArguments,
const std::multimap<Function*, CallSite> &CallSites) {
DEBUG(std::cerr << " MaybeLive argument now live: " << Arg->getName()<<"\n");
assert(MaybeLiveArguments.count(Arg) && !LiveArguments.count(Arg) &&
"Arg not MaybeLive?");
MaybeLiveArguments.erase(Arg);
LiveArguments.insert(Arg);
// Loop over all of the call sites of the function, making any arguments
// passed in to provide a value for this argument live as necessary.
//
Function *Fn = Arg->getParent();
unsigned ArgNo = std::distance(Fn->abegin(), Function::aiterator(Arg));
std::multimap<Function*, CallSite>::const_iterator I =
CallSites.lower_bound(Fn);
for (; I != CallSites.end() && I->first == Fn; ++I) {
const CallSite &CS = I->second;
if (Argument *ActualArg = dyn_cast<Argument>(*(CS.arg_begin()+ArgNo)))
if (MaybeLiveArguments.count(ActualArg))
MarkArgumentLive(ActualArg, MaybeLiveArguments, LiveArguments,
CallSites);
}
}
// RemoveDeadArgumentsFromFunction - We know that F has dead arguments, as
// specified by the DeadArguments list. Transform the function and all of the
// callees of the function to not have these arguments.
//
void DAE::RemoveDeadArgumentsFromFunction(Function *F,
std::set<Argument*> &DeadArguments){
// Start by computing a new prototype for the function, which is the same as
// the old function, but has fewer arguments.
const FunctionType *FTy = F->getFunctionType();
std::vector<const Type*> Params;
for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
if (!DeadArguments.count(I))
Params.push_back(I->getType());
FunctionType *NFTy = FunctionType::get(FTy->getReturnType(), Params,
FTy->isVarArg());
// 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);
// Loop over all of the callers of the function, transforming the call sites
// to pass in a smaller number of arguments into the new function.
//
while (!F->use_empty()) {
CallSite CS = CallSite::get(F->use_back());
Instruction *Call = CS.getInstruction();
CS.setCalledFunction(NF); // Reduce the uses count of F
// Loop over the operands, deleting dead ones...
CallSite::arg_iterator AI = CS.arg_begin();
for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
if (DeadArguments.count(I)) { // Remove operands for dead arguments
AI = Call->op_erase(AI);
} else {
++AI; // Leave live operands alone...
}
}
// Since we have now created the new function, splice the body of the old
// function right into the new function, leaving the old rotting hulk of the
// function empty.
NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
// Loop over the argument list, transfering uses of the old arguments over to
// the new arguments, also transfering over the names as well. While we're at
// it, remove the dead arguments from the DeadArguments list.
//
for (Function::aiterator I = F->abegin(), E = F->aend(), I2 = NF->abegin();
I != E; ++I)
if (!DeadArguments.count(I)) {
// If this is a live argument, move the name and users over to the new
// version.
I->replaceAllUsesWith(I2);
I2->setName(I->getName());
++I2;
} else {
// If this argument is dead, replace any uses of it with null constants
// (these are guaranteed to only be operands to call instructions which
// will later be simplified).
I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
DeadArguments.erase(I);
}
// Now that the old function is dead, delete it.
F->getParent()->getFunctionList().erase(F);
}
bool DAE::run(Module &M) {
// First phase: loop through the module, determining which arguments are live.
// We assume all arguments are dead unless proven otherwise (allowing us to
// determing that dead arguments passed into recursive functions are dead).
//
std::set<Argument*> LiveArguments, MaybeLiveArguments, DeadArguments;
std::multimap<Function*, CallSite> CallSites;
DEBUG(std::cerr << "DAE - Determining liveness\n");
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
Function &Fn = *I;
// If the function is intrinsically alive, just mark the arguments alive.
if (FunctionArgumentsIntrinsicallyAlive(Fn)) {
for (Function::aiterator AI = Fn.abegin(), E = Fn.aend(); AI != E; ++AI)
LiveArguments.insert(AI);
DEBUG(std::cerr << " Args intrinsically live for fn: " << Fn.getName()
<< "\n");
} else {
DEBUG(std::cerr << " Inspecting args for fn: " << Fn.getName() << "\n");
// If it is not intrinsically alive, we know that all users of the
// function are call sites. Mark all of the arguments live which are
// directly used, and keep track of all of the call sites of this function
// if there are any arguments we assume that are dead.
//
bool AnyMaybeLiveArgs = false;
for (Function::aiterator AI = Fn.abegin(), E = Fn.aend(); AI != E; ++AI)
switch (getArgumentLiveness(*AI)) {
case Alive:
DEBUG(std::cerr << " Arg live by use: " << AI->getName() << "\n");
LiveArguments.insert(AI);
break;
case Dead:
DEBUG(std::cerr << " Arg definitely dead: " <<AI->getName()<<"\n");
DeadArguments.insert(AI);
break;
case MaybeLive:
DEBUG(std::cerr << " Arg only passed to calls: "
<< AI->getName() << "\n");
AnyMaybeLiveArgs = true;
MaybeLiveArguments.insert(AI);
break;
}
// If there are any "MaybeLive" arguments, we need to check callees of
// this function when/if they become alive. Record which functions are
// callees...
if (AnyMaybeLiveArgs)
for (Value::use_iterator I = Fn.use_begin(), E = Fn.use_end();
I != E; ++I)
CallSites.insert(std::make_pair(&Fn, CallSite::get(*I)));
}
}
// Now we loop over all of the MaybeLive arguments, promoting them to be live
// arguments if one of the calls that uses the arguments to the calls they are
// passed into requires them to be live. Of course this could make other
// arguments live, so process callers recursively.
//
// Because elements can be removed from the MaybeLiveArguments list, copy it
// to a temporary vector.
//
std::vector<Argument*> TmpArgList(MaybeLiveArguments.begin(),
MaybeLiveArguments.end());
for (unsigned i = 0, e = TmpArgList.size(); i != e; ++i) {
Argument *MLA = TmpArgList[i];
if (MaybeLiveArguments.count(MLA) &&
isMaybeLiveArgumentNowAlive(MLA, LiveArguments)) {
MarkArgumentLive(MLA, MaybeLiveArguments, LiveArguments, CallSites);
}
}
// Recover memory early...
CallSites.clear();
// At this point, we know that all arguments in DeadArguments and
// MaybeLiveArguments are dead. If the two sets are empty, there is nothing
// to do.
if (MaybeLiveArguments.empty() && DeadArguments.empty())
return false;
// Otherwise, compact into one set, and start eliminating the arguments from
// the functions.
DeadArguments.insert(MaybeLiveArguments.begin(), MaybeLiveArguments.end());
MaybeLiveArguments.clear();
NumArgumentsEliminated += DeadArguments.size();
while (!DeadArguments.empty())
RemoveDeadArgumentsFromFunction((*DeadArguments.begin())->getParent(),
DeadArguments);
return true;
}