--- /dev/null
+//===-- 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/Statistic.h"
+#include "Support/iterator"
+#include <set>
+
+namespace {
+ Statistic<> NumArgumentsEliminated("deadargelim", "Number of args removed");
+
+ struct DAE : public Pass {
+ bool run(Module &M);
+ };
+ RegisterOpt<DAE> X("deadargelim", "Dead Argument Elimination");
+}
+
+// createDeadArgEliminationPass - This pass removes arguments from functions
+// which are not used by the body of the function.
+//
+Pass *createDeadArgEliminationPass() { return new DAE(); }
+
+
+// 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".
+//
+static bool FunctionArgumentsIntrinsicallyAlive(const Function &F) {
+ if (!F.hasInternalLinkage()) 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;
+
+ // FIXME: check to see if it's passed through a va_arg area
+ }
+
+ 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.
+//
+static void 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, Function::InternalLinkage, 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 definately 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;
+}
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