forked from OSchip/llvm-project
942 lines
36 KiB
C++
942 lines
36 KiB
C++
//===-- DeadArgumentElimination.cpp - Eliminate dead arguments ------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass deletes dead arguments from internal functions. Dead argument
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// elimination removes arguments which are directly dead, as well as arguments
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// only passed into function calls as dead arguments of other functions. This
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// pass also deletes dead return values in a similar way.
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//
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// This pass is often useful as a cleanup pass to run after aggressive
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// interprocedural passes, which add possibly-dead arguments or return values.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "deadargelim"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/CallingConv.h"
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#include "llvm/Constant.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/StringExtras.h"
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#include <map>
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#include <set>
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using namespace llvm;
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STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
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STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
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namespace {
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/// DAE - The dead argument elimination pass.
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///
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class DAE : public ModulePass {
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public:
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/// Struct that represents (part of) either a return value or a function
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/// argument. Used so that arguments and return values can be used
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/// interchangably.
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struct RetOrArg {
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RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
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IsArg(IsArg) {}
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const Function *F;
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unsigned Idx;
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bool IsArg;
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/// Make RetOrArg comparable, so we can put it into a map.
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bool operator<(const RetOrArg &O) const {
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if (F != O.F)
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return F < O.F;
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else if (Idx != O.Idx)
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return Idx < O.Idx;
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else
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return IsArg < O.IsArg;
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}
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/// Make RetOrArg comparable, so we can easily iterate the multimap.
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bool operator==(const RetOrArg &O) const {
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return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
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}
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std::string getDescription() const {
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return std::string((IsArg ? "Argument #" : "Return value #"))
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+ utostr(Idx) + " of function " + F->getNameStr();
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}
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};
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/// Liveness enum - During our initial pass over the program, we determine
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/// that things are either alive or maybe alive. We don't mark anything
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/// explicitly dead (even if we know they are), since anything not alive
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/// with no registered uses (in Uses) will never be marked alive and will
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/// thus become dead in the end.
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enum Liveness { Live, MaybeLive };
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/// Convenience wrapper
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RetOrArg CreateRet(const Function *F, unsigned Idx) {
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return RetOrArg(F, Idx, false);
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}
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/// Convenience wrapper
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RetOrArg CreateArg(const Function *F, unsigned Idx) {
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return RetOrArg(F, Idx, true);
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}
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typedef std::multimap<RetOrArg, RetOrArg> UseMap;
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/// This maps a return value or argument to any MaybeLive return values or
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/// arguments it uses. This allows the MaybeLive values to be marked live
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/// when any of its users is marked live.
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/// For example (indices are left out for clarity):
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/// - Uses[ret F] = ret G
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/// This means that F calls G, and F returns the value returned by G.
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/// - Uses[arg F] = ret G
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/// This means that some function calls G and passes its result as an
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/// argument to F.
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/// - Uses[ret F] = arg F
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/// This means that F returns one of its own arguments.
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/// - Uses[arg F] = arg G
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/// This means that G calls F and passes one of its own (G's) arguments
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/// directly to F.
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UseMap Uses;
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typedef std::set<RetOrArg> LiveSet;
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typedef std::set<const Function*> LiveFuncSet;
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/// This set contains all values that have been determined to be live.
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LiveSet LiveValues;
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/// This set contains all values that are cannot be changed in any way.
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LiveFuncSet LiveFunctions;
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typedef SmallVector<RetOrArg, 5> UseVector;
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protected:
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// DAH uses this to specify a different ID.
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explicit DAE(void *ID) : ModulePass(ID) {}
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public:
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static char ID; // Pass identification, replacement for typeid
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DAE() : ModulePass(&ID) {}
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bool runOnModule(Module &M);
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virtual bool ShouldHackArguments() const { return false; }
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private:
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Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
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Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses,
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unsigned RetValNum = 0);
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Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses);
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void SurveyFunction(const Function &F);
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void MarkValue(const RetOrArg &RA, Liveness L,
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const UseVector &MaybeLiveUses);
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void MarkLive(const RetOrArg &RA);
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void MarkLive(const Function &F);
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void PropagateLiveness(const RetOrArg &RA);
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bool RemoveDeadStuffFromFunction(Function *F);
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bool DeleteDeadVarargs(Function &Fn);
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};
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}
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char DAE::ID = 0;
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static RegisterPass<DAE>
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X("deadargelim", "Dead Argument Elimination");
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namespace {
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/// DAH - DeadArgumentHacking pass - Same as dead argument elimination, but
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/// deletes arguments to functions which are external. This is only for use
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/// by bugpoint.
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struct DAH : public DAE {
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static char ID;
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DAH() : DAE(&ID) {}
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virtual bool ShouldHackArguments() const { return true; }
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};
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}
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char DAH::ID = 0;
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static RegisterPass<DAH>
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Y("deadarghaX0r", "Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)");
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/// createDeadArgEliminationPass - This pass removes arguments from functions
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/// which are not used by the body of the function.
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///
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ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
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ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
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/// DeleteDeadVarargs - If this is an function that takes a ... list, and if
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/// llvm.vastart is never called, the varargs list is dead for the function.
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bool DAE::DeleteDeadVarargs(Function &Fn) {
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assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
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if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
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// Ensure that the function is only directly called.
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if (Fn.hasAddressTaken())
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return false;
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// Okay, we know we can transform this function if safe. Scan its body
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// looking for calls to llvm.vastart.
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for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
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for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
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if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
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if (II->getIntrinsicID() == Intrinsic::vastart)
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return false;
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}
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}
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}
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// If we get here, there are no calls to llvm.vastart in the function body,
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// remove the "..." and adjust all the calls.
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// Start by computing a new prototype for the function, which is the same as
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// the old function, but doesn't have isVarArg set.
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const FunctionType *FTy = Fn.getFunctionType();
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std::vector<const Type*> Params(FTy->param_begin(), FTy->param_end());
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FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
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Params, false);
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unsigned NumArgs = Params.size();
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// Create the new function body and insert it into the module...
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Function *NF = Function::Create(NFTy, Fn.getLinkage());
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NF->copyAttributesFrom(&Fn);
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Fn.getParent()->getFunctionList().insert(&Fn, NF);
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NF->takeName(&Fn);
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// Loop over all of the callers of the function, transforming the call sites
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// to pass in a smaller number of arguments into the new function.
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//
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std::vector<Value*> Args;
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while (!Fn.use_empty()) {
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CallSite CS = CallSite::get(Fn.use_back());
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Instruction *Call = CS.getInstruction();
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// Pass all the same arguments.
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Args.assign(CS.arg_begin(), CS.arg_begin()+NumArgs);
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// Drop any attributes that were on the vararg arguments.
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AttrListPtr PAL = CS.getAttributes();
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if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
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SmallVector<AttributeWithIndex, 8> AttributesVec;
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for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
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AttributesVec.push_back(PAL.getSlot(i));
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if (Attributes FnAttrs = PAL.getFnAttributes())
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AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
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PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end());
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}
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Instruction *New;
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if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
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New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
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Args.begin(), Args.end(), "", Call);
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cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
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cast<InvokeInst>(New)->setAttributes(PAL);
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} else {
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New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
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cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
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cast<CallInst>(New)->setAttributes(PAL);
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if (cast<CallInst>(Call)->isTailCall())
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cast<CallInst>(New)->setTailCall();
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}
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if (MDNode *N = Call->getDbgMetadata())
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New->setDbgMetadata(N);
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Args.clear();
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if (!Call->use_empty())
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Call->replaceAllUsesWith(New);
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New->takeName(Call);
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// Finally, remove the old call from the program, reducing the use-count of
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// F.
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Call->eraseFromParent();
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}
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// Since we have now created the new function, splice the body of the old
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// function right into the new function, leaving the old rotting hulk of the
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// function empty.
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NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
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// Loop over the argument list, transfering uses of the old arguments over to
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// the new arguments, also transfering over the names as well. While we're at
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// it, remove the dead arguments from the DeadArguments list.
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//
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for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
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I2 = NF->arg_begin(); I != E; ++I, ++I2) {
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// Move the name and users over to the new version.
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I->replaceAllUsesWith(I2);
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I2->takeName(I);
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}
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// Finally, nuke the old function.
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Fn.eraseFromParent();
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return true;
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}
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/// Convenience function that returns the number of return values. It returns 0
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/// for void functions and 1 for functions not returning a struct. It returns
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/// the number of struct elements for functions returning a struct.
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static unsigned NumRetVals(const Function *F) {
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if (F->getReturnType()->isVoidTy())
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return 0;
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else if (const StructType *STy = dyn_cast<StructType>(F->getReturnType()))
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return STy->getNumElements();
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else
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return 1;
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}
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/// MarkIfNotLive - This checks Use for liveness in LiveValues. If Use is not
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/// live, it adds Use to the MaybeLiveUses argument. Returns the determined
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/// liveness of Use.
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DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
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// We're live if our use or its Function is already marked as live.
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if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
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return Live;
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// We're maybe live otherwise, but remember that we must become live if
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// Use becomes live.
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MaybeLiveUses.push_back(Use);
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return MaybeLive;
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}
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/// SurveyUse - This looks at a single use of an argument or return value
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/// and determines if it should be alive or not. Adds this use to MaybeLiveUses
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/// if it causes the used value to become MaybeLive.
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///
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/// RetValNum is the return value number to use when this use is used in a
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/// return instruction. This is used in the recursion, you should always leave
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/// it at 0.
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DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U,
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UseVector &MaybeLiveUses, unsigned RetValNum) {
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const User *V = *U;
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if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
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// The value is returned from a function. It's only live when the
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// function's return value is live. We use RetValNum here, for the case
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// that U is really a use of an insertvalue instruction that uses the
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// orginal Use.
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RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
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// We might be live, depending on the liveness of Use.
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return MarkIfNotLive(Use, MaybeLiveUses);
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}
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if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
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if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
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&& IV->hasIndices())
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// The use we are examining is inserted into an aggregate. Our liveness
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// depends on all uses of that aggregate, but if it is used as a return
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// value, only index at which we were inserted counts.
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RetValNum = *IV->idx_begin();
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// Note that if we are used as the aggregate operand to the insertvalue,
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// we don't change RetValNum, but do survey all our uses.
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Liveness Result = MaybeLive;
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for (Value::const_use_iterator I = IV->use_begin(),
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E = V->use_end(); I != E; ++I) {
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Result = SurveyUse(I, MaybeLiveUses, RetValNum);
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if (Result == Live)
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break;
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}
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return Result;
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}
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if (ImmutableCallSite CS = V) {
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const Function *F = CS.getCalledFunction();
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if (F) {
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// Used in a direct call.
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// Find the argument number. We know for sure that this use is an
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// argument, since if it was the function argument this would be an
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// indirect call and the we know can't be looking at a value of the
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// label type (for the invoke instruction).
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unsigned ArgNo = CS.getArgumentNo(U);
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if (ArgNo >= F->getFunctionType()->getNumParams())
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// The value is passed in through a vararg! Must be live.
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return Live;
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assert(CS.getArgument(ArgNo)
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== CS->getOperand(U.getOperandNo())
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&& "Argument is not where we expected it");
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// Value passed to a normal call. It's only live when the corresponding
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// argument to the called function turns out live.
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RetOrArg Use = CreateArg(F, ArgNo);
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return MarkIfNotLive(Use, MaybeLiveUses);
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}
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}
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// Used in any other way? Value must be live.
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return Live;
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}
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/// SurveyUses - This looks at all the uses of the given value
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/// Returns the Liveness deduced from the uses of this value.
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///
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/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
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/// the result is Live, MaybeLiveUses might be modified but its content should
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/// be ignored (since it might not be complete).
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DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
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// Assume it's dead (which will only hold if there are no uses at all..).
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Liveness Result = MaybeLive;
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// Check each use.
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for (Value::const_use_iterator I = V->use_begin(),
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E = V->use_end(); I != E; ++I) {
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Result = SurveyUse(I, MaybeLiveUses);
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if (Result == Live)
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break;
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}
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return Result;
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}
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// SurveyFunction - This performs the initial survey of the specified function,
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// checking out whether or not it uses any of its incoming arguments or whether
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// any callers use the return value. This fills in the LiveValues set and Uses
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// map.
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//
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// We consider arguments of non-internal functions to be intrinsically alive as
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// well as arguments to functions which have their "address taken".
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//
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void DAE::SurveyFunction(const Function &F) {
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unsigned RetCount = NumRetVals(&F);
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// Assume all return values are dead
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typedef SmallVector<Liveness, 5> RetVals;
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RetVals RetValLiveness(RetCount, MaybeLive);
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typedef SmallVector<UseVector, 5> RetUses;
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// These vectors map each return value to the uses that make it MaybeLive, so
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// we can add those to the Uses map if the return value really turns out to be
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// MaybeLive. Initialized to a list of RetCount empty lists.
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RetUses MaybeLiveRetUses(RetCount);
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for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
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if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
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if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
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!= F.getFunctionType()->getReturnType()) {
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// We don't support old style multiple return values.
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MarkLive(F);
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return;
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}
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if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
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MarkLive(F);
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return;
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}
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DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
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// Keep track of the number of live retvals, so we can skip checks once all
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// of them turn out to be live.
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unsigned NumLiveRetVals = 0;
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const Type *STy = dyn_cast<StructType>(F.getReturnType());
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// Loop all uses of the function.
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for (Value::const_use_iterator I = F.use_begin(), E = F.use_end();
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I != E; ++I) {
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// If the function is PASSED IN as an argument, its address has been
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// taken.
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ImmutableCallSite CS(*I);
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if (!CS || !CS.isCallee(I)) {
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MarkLive(F);
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return;
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}
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// If this use is anything other than a call site, the function is alive.
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const Instruction *TheCall = CS.getInstruction();
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if (!TheCall) { // Not a direct call site?
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MarkLive(F);
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return;
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}
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// If we end up here, we are looking at a direct call to our function.
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// Now, check how our return value(s) is/are used in this caller. Don't
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// bother checking return values if all of them are live already.
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if (NumLiveRetVals != RetCount) {
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if (STy) {
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// Check all uses of the return value.
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for (Value::const_use_iterator I = TheCall->use_begin(),
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E = TheCall->use_end(); I != E; ++I) {
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const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
|
|
if (Ext && Ext->hasIndices()) {
|
|
// This use uses a part of our return value, survey the uses of
|
|
// that part and store the results for this index only.
|
|
unsigned Idx = *Ext->idx_begin();
|
|
if (RetValLiveness[Idx] != Live) {
|
|
RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
|
|
if (RetValLiveness[Idx] == Live)
|
|
NumLiveRetVals++;
|
|
}
|
|
} else {
|
|
// Used by something else than extractvalue. Mark all return
|
|
// values as live.
|
|
for (unsigned i = 0; i != RetCount; ++i )
|
|
RetValLiveness[i] = Live;
|
|
NumLiveRetVals = RetCount;
|
|
break;
|
|
}
|
|
}
|
|
} else {
|
|
// Single return value
|
|
RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
|
|
if (RetValLiveness[0] == Live)
|
|
NumLiveRetVals = RetCount;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Now we've inspected all callers, record the liveness of our return values.
|
|
for (unsigned i = 0; i != RetCount; ++i)
|
|
MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
|
|
|
|
DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
|
|
|
|
// Now, check all of our arguments.
|
|
unsigned i = 0;
|
|
UseVector MaybeLiveArgUses;
|
|
for (Function::const_arg_iterator AI = F.arg_begin(),
|
|
E = F.arg_end(); AI != E; ++AI, ++i) {
|
|
// See what the effect of this use is (recording any uses that cause
|
|
// MaybeLive in MaybeLiveArgUses).
|
|
Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
|
|
// Mark the result.
|
|
MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
|
|
// Clear the vector again for the next iteration.
|
|
MaybeLiveArgUses.clear();
|
|
}
|
|
}
|
|
|
|
/// MarkValue - This function marks the liveness of RA depending on L. If L is
|
|
/// MaybeLive, it also takes all uses in MaybeLiveUses and records them in Uses,
|
|
/// such that RA will be marked live if any use in MaybeLiveUses gets marked
|
|
/// live later on.
|
|
void DAE::MarkValue(const RetOrArg &RA, Liveness L,
|
|
const UseVector &MaybeLiveUses) {
|
|
switch (L) {
|
|
case Live: MarkLive(RA); break;
|
|
case MaybeLive:
|
|
{
|
|
// Note any uses of this value, so this return value can be
|
|
// marked live whenever one of the uses becomes live.
|
|
for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
|
|
UE = MaybeLiveUses.end(); UI != UE; ++UI)
|
|
Uses.insert(std::make_pair(*UI, RA));
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
/// MarkLive - Mark the given Function as alive, meaning that it cannot be
|
|
/// changed in any way. Additionally,
|
|
/// mark any values that are used as this function's parameters or by its return
|
|
/// values (according to Uses) live as well.
|
|
void DAE::MarkLive(const Function &F) {
|
|
DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
|
|
// Mark the function as live.
|
|
LiveFunctions.insert(&F);
|
|
// Mark all arguments as live.
|
|
for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
|
|
PropagateLiveness(CreateArg(&F, i));
|
|
// Mark all return values as live.
|
|
for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
|
|
PropagateLiveness(CreateRet(&F, i));
|
|
}
|
|
|
|
/// MarkLive - Mark the given return value or argument as live. Additionally,
|
|
/// mark any values that are used by this value (according to Uses) live as
|
|
/// well.
|
|
void DAE::MarkLive(const RetOrArg &RA) {
|
|
if (LiveFunctions.count(RA.F))
|
|
return; // Function was already marked Live.
|
|
|
|
if (!LiveValues.insert(RA).second)
|
|
return; // We were already marked Live.
|
|
|
|
DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
|
|
PropagateLiveness(RA);
|
|
}
|
|
|
|
/// PropagateLiveness - Given that RA is a live value, propagate it's liveness
|
|
/// to any other values it uses (according to Uses).
|
|
void DAE::PropagateLiveness(const RetOrArg &RA) {
|
|
// We don't use upper_bound (or equal_range) here, because our recursive call
|
|
// to ourselves is likely to cause the upper_bound (which is the first value
|
|
// not belonging to RA) to become erased and the iterator invalidated.
|
|
UseMap::iterator Begin = Uses.lower_bound(RA);
|
|
UseMap::iterator E = Uses.end();
|
|
UseMap::iterator I;
|
|
for (I = Begin; I != E && I->first == RA; ++I)
|
|
MarkLive(I->second);
|
|
|
|
// Erase RA from the Uses map (from the lower bound to wherever we ended up
|
|
// after the loop).
|
|
Uses.erase(Begin, I);
|
|
}
|
|
|
|
// RemoveDeadStuffFromFunction - Remove any arguments and return values from F
|
|
// that are not in LiveValues. Transform the function and all of the callees of
|
|
// the function to not have these arguments and return values.
|
|
//
|
|
bool DAE::RemoveDeadStuffFromFunction(Function *F) {
|
|
// Don't modify fully live functions
|
|
if (LiveFunctions.count(F))
|
|
return false;
|
|
|
|
// Start by computing a new prototype for the function, which is the same as
|
|
// the old function, but has fewer arguments and a different return type.
|
|
const FunctionType *FTy = F->getFunctionType();
|
|
std::vector<const Type*> Params;
|
|
|
|
// Set up to build a new list of parameter attributes.
|
|
SmallVector<AttributeWithIndex, 8> AttributesVec;
|
|
const AttrListPtr &PAL = F->getAttributes();
|
|
|
|
// The existing function return attributes.
|
|
Attributes RAttrs = PAL.getRetAttributes();
|
|
Attributes FnAttrs = PAL.getFnAttributes();
|
|
|
|
// Find out the new return value.
|
|
|
|
const Type *RetTy = FTy->getReturnType();
|
|
const Type *NRetTy = NULL;
|
|
unsigned RetCount = NumRetVals(F);
|
|
|
|
// -1 means unused, other numbers are the new index
|
|
SmallVector<int, 5> NewRetIdxs(RetCount, -1);
|
|
std::vector<const Type*> RetTypes;
|
|
if (RetTy->isVoidTy()) {
|
|
NRetTy = RetTy;
|
|
} else {
|
|
const StructType *STy = dyn_cast<StructType>(RetTy);
|
|
if (STy)
|
|
// Look at each of the original return values individually.
|
|
for (unsigned i = 0; i != RetCount; ++i) {
|
|
RetOrArg Ret = CreateRet(F, i);
|
|
if (LiveValues.erase(Ret)) {
|
|
RetTypes.push_back(STy->getElementType(i));
|
|
NewRetIdxs[i] = RetTypes.size() - 1;
|
|
} else {
|
|
++NumRetValsEliminated;
|
|
DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
|
|
<< F->getName() << "\n");
|
|
}
|
|
}
|
|
else
|
|
// We used to return a single value.
|
|
if (LiveValues.erase(CreateRet(F, 0))) {
|
|
RetTypes.push_back(RetTy);
|
|
NewRetIdxs[0] = 0;
|
|
} else {
|
|
DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
|
|
<< "\n");
|
|
++NumRetValsEliminated;
|
|
}
|
|
if (RetTypes.size() > 1)
|
|
// More than one return type? Return a struct with them. Also, if we used
|
|
// to return a struct and didn't change the number of return values,
|
|
// return a struct again. This prevents changing {something} into
|
|
// something and {} into void.
|
|
// Make the new struct packed if we used to return a packed struct
|
|
// already.
|
|
NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
|
|
else if (RetTypes.size() == 1)
|
|
// One return type? Just a simple value then, but only if we didn't use to
|
|
// return a struct with that simple value before.
|
|
NRetTy = RetTypes.front();
|
|
else if (RetTypes.size() == 0)
|
|
// No return types? Make it void, but only if we didn't use to return {}.
|
|
NRetTy = Type::getVoidTy(F->getContext());
|
|
}
|
|
|
|
assert(NRetTy && "No new return type found?");
|
|
|
|
// Remove any incompatible attributes, but only if we removed all return
|
|
// values. Otherwise, ensure that we don't have any conflicting attributes
|
|
// here. Currently, this should not be possible, but special handling might be
|
|
// required when new return value attributes are added.
|
|
if (NRetTy->isVoidTy())
|
|
RAttrs &= ~Attribute::typeIncompatible(NRetTy);
|
|
else
|
|
assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0
|
|
&& "Return attributes no longer compatible?");
|
|
|
|
if (RAttrs)
|
|
AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
|
|
|
|
// Remember which arguments are still alive.
|
|
SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
|
|
// Construct the new parameter list from non-dead arguments. Also construct
|
|
// a new set of parameter attributes to correspond. Skip the first parameter
|
|
// attribute, since that belongs to the return value.
|
|
unsigned i = 0;
|
|
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
|
|
I != E; ++I, ++i) {
|
|
RetOrArg Arg = CreateArg(F, i);
|
|
if (LiveValues.erase(Arg)) {
|
|
Params.push_back(I->getType());
|
|
ArgAlive[i] = true;
|
|
|
|
// Get the original parameter attributes (skipping the first one, that is
|
|
// for the return value.
|
|
if (Attributes Attrs = PAL.getParamAttributes(i + 1))
|
|
AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs));
|
|
} else {
|
|
++NumArgumentsEliminated;
|
|
DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
|
|
<< ") from " << F->getName() << "\n");
|
|
}
|
|
}
|
|
|
|
if (FnAttrs != Attribute::None)
|
|
AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
|
|
|
|
// Reconstruct the AttributesList based on the vector we constructed.
|
|
AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(),
|
|
AttributesVec.end());
|
|
|
|
// Create the new function type based on the recomputed parameters.
|
|
FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
|
|
|
|
// No change?
|
|
if (NFTy == FTy)
|
|
return false;
|
|
|
|
// Create the new function body and insert it into the module...
|
|
Function *NF = Function::Create(NFTy, F->getLinkage());
|
|
NF->copyAttributesFrom(F);
|
|
NF->setAttributes(NewPAL);
|
|
// Insert the new function before the old function, so we won't be processing
|
|
// it again.
|
|
F->getParent()->getFunctionList().insert(F, NF);
|
|
NF->takeName(F);
|
|
|
|
// 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.
|
|
//
|
|
std::vector<Value*> Args;
|
|
while (!F->use_empty()) {
|
|
CallSite CS = CallSite::get(F->use_back());
|
|
Instruction *Call = CS.getInstruction();
|
|
|
|
AttributesVec.clear();
|
|
const AttrListPtr &CallPAL = CS.getAttributes();
|
|
|
|
// The call return attributes.
|
|
Attributes RAttrs = CallPAL.getRetAttributes();
|
|
Attributes FnAttrs = CallPAL.getFnAttributes();
|
|
// Adjust in case the function was changed to return void.
|
|
RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType());
|
|
if (RAttrs)
|
|
AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
|
|
|
|
// Declare these outside of the loops, so we can reuse them for the second
|
|
// loop, which loops the varargs.
|
|
CallSite::arg_iterator I = CS.arg_begin();
|
|
unsigned i = 0;
|
|
// Loop over those operands, corresponding to the normal arguments to the
|
|
// original function, and add those that are still alive.
|
|
for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
|
|
if (ArgAlive[i]) {
|
|
Args.push_back(*I);
|
|
// Get original parameter attributes, but skip return attributes.
|
|
if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
|
|
AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
|
|
}
|
|
|
|
// Push any varargs arguments on the list. Don't forget their attributes.
|
|
for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
|
|
Args.push_back(*I);
|
|
if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
|
|
AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
|
|
}
|
|
|
|
if (FnAttrs != Attribute::None)
|
|
AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
|
|
|
|
// Reconstruct the AttributesList based on the vector we constructed.
|
|
AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(),
|
|
AttributesVec.end());
|
|
|
|
Instruction *New;
|
|
if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
|
|
New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
|
|
Args.begin(), Args.end(), "", Call);
|
|
cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
|
|
cast<InvokeInst>(New)->setAttributes(NewCallPAL);
|
|
} else {
|
|
New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
|
|
cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
|
|
cast<CallInst>(New)->setAttributes(NewCallPAL);
|
|
if (cast<CallInst>(Call)->isTailCall())
|
|
cast<CallInst>(New)->setTailCall();
|
|
}
|
|
if (MDNode *N = Call->getDbgMetadata())
|
|
New->setDbgMetadata(N);
|
|
|
|
Args.clear();
|
|
|
|
if (!Call->use_empty()) {
|
|
if (New->getType() == Call->getType()) {
|
|
// Return type not changed? Just replace users then.
|
|
Call->replaceAllUsesWith(New);
|
|
New->takeName(Call);
|
|
} else if (New->getType()->isVoidTy()) {
|
|
// Our return value has uses, but they will get removed later on.
|
|
// Replace by null for now.
|
|
Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
|
|
} else {
|
|
assert(RetTy->isStructTy() &&
|
|
"Return type changed, but not into a void. The old return type"
|
|
" must have been a struct!");
|
|
Instruction *InsertPt = Call;
|
|
if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
|
|
BasicBlock::iterator IP = II->getNormalDest()->begin();
|
|
while (isa<PHINode>(IP)) ++IP;
|
|
InsertPt = IP;
|
|
}
|
|
|
|
// We used to return a struct. Instead of doing smart stuff with all the
|
|
// uses of this struct, we will just rebuild it using
|
|
// extract/insertvalue chaining and let instcombine clean that up.
|
|
//
|
|
// Start out building up our return value from undef
|
|
Value *RetVal = UndefValue::get(RetTy);
|
|
for (unsigned i = 0; i != RetCount; ++i)
|
|
if (NewRetIdxs[i] != -1) {
|
|
Value *V;
|
|
if (RetTypes.size() > 1)
|
|
// We are still returning a struct, so extract the value from our
|
|
// return value
|
|
V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
|
|
InsertPt);
|
|
else
|
|
// We are now returning a single element, so just insert that
|
|
V = New;
|
|
// Insert the value at the old position
|
|
RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
|
|
}
|
|
// Now, replace all uses of the old call instruction with the return
|
|
// struct we built
|
|
Call->replaceAllUsesWith(RetVal);
|
|
New->takeName(Call);
|
|
}
|
|
}
|
|
|
|
// Finally, remove the old call from the program, reducing the use-count of
|
|
// F.
|
|
Call->eraseFromParent();
|
|
}
|
|
|
|
// 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.
|
|
i = 0;
|
|
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
|
|
I2 = NF->arg_begin(); I != E; ++I, ++i)
|
|
if (ArgAlive[i]) {
|
|
// If this is a live argument, move the name and users over to the new
|
|
// version.
|
|
I->replaceAllUsesWith(I2);
|
|
I2->takeName(I);
|
|
++I2;
|
|
} else {
|
|
// If this argument is dead, replace any uses of it with null constants
|
|
// (these are guaranteed to become unused later on).
|
|
I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
|
|
}
|
|
|
|
// If we change the return value of the function we must rewrite any return
|
|
// instructions. Check this now.
|
|
if (F->getReturnType() != NF->getReturnType())
|
|
for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
|
|
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
|
|
Value *RetVal;
|
|
|
|
if (NFTy->getReturnType()->isVoidTy()) {
|
|
RetVal = 0;
|
|
} else {
|
|
assert (RetTy->isStructTy());
|
|
// The original return value was a struct, insert
|
|
// extractvalue/insertvalue chains to extract only the values we need
|
|
// to return and insert them into our new result.
|
|
// This does generate messy code, but we'll let it to instcombine to
|
|
// clean that up.
|
|
Value *OldRet = RI->getOperand(0);
|
|
// Start out building up our return value from undef
|
|
RetVal = UndefValue::get(NRetTy);
|
|
for (unsigned i = 0; i != RetCount; ++i)
|
|
if (NewRetIdxs[i] != -1) {
|
|
ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
|
|
"oldret", RI);
|
|
if (RetTypes.size() > 1) {
|
|
// We're still returning a struct, so reinsert the value into
|
|
// our new return value at the new index
|
|
|
|
RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
|
|
"newret", RI);
|
|
} else {
|
|
// We are now only returning a simple value, so just return the
|
|
// extracted value.
|
|
RetVal = EV;
|
|
}
|
|
}
|
|
}
|
|
// Replace the return instruction with one returning the new return
|
|
// value (possibly 0 if we became void).
|
|
ReturnInst::Create(F->getContext(), RetVal, RI);
|
|
BB->getInstList().erase(RI);
|
|
}
|
|
|
|
// Now that the old function is dead, delete it.
|
|
F->eraseFromParent();
|
|
|
|
return true;
|
|
}
|
|
|
|
bool DAE::runOnModule(Module &M) {
|
|
bool Changed = false;
|
|
|
|
// First pass: Do a simple check to see if any functions can have their "..."
|
|
// removed. We can do this if they never call va_start. This loop cannot be
|
|
// fused with the next loop, because deleting a function invalidates
|
|
// information computed while surveying other functions.
|
|
DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
|
|
for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
|
|
Function &F = *I++;
|
|
if (F.getFunctionType()->isVarArg())
|
|
Changed |= DeleteDeadVarargs(F);
|
|
}
|
|
|
|
// Second phase:loop through the module, determining which arguments are live.
|
|
// We assume all arguments are dead unless proven otherwise (allowing us to
|
|
// determine that dead arguments passed into recursive functions are dead).
|
|
//
|
|
DEBUG(dbgs() << "DAE - Determining liveness\n");
|
|
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
|
|
SurveyFunction(*I);
|
|
|
|
// Now, remove all dead arguments and return values from each function in
|
|
// turn.
|
|
for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
|
|
// Increment now, because the function will probably get removed (ie.
|
|
// replaced by a new one).
|
|
Function *F = I++;
|
|
Changed |= RemoveDeadStuffFromFunction(F);
|
|
}
|
|
return Changed;
|
|
}
|