DeadArgumentElimination.h revision 303231
1303231Sdim//===- DeadArgumentElimination.h - Eliminate Dead Args ----------*- C++ -*-===// 2303231Sdim// 3303231Sdim// The LLVM Compiler Infrastructure 4303231Sdim// 5303231Sdim// This file is distributed under the University of Illinois Open Source 6303231Sdim// License. See LICENSE.TXT for details. 7303231Sdim// 8303231Sdim//===----------------------------------------------------------------------===// 9303231Sdim// 10303231Sdim// This pass deletes dead arguments from internal functions. Dead argument 11303231Sdim// elimination removes arguments which are directly dead, as well as arguments 12303231Sdim// only passed into function calls as dead arguments of other functions. This 13303231Sdim// pass also deletes dead return values in a similar way. 14303231Sdim// 15303231Sdim// This pass is often useful as a cleanup pass to run after aggressive 16303231Sdim// interprocedural passes, which add possibly-dead arguments or return values. 17303231Sdim// 18303231Sdim//===----------------------------------------------------------------------===// 19303231Sdim 20303231Sdim#ifndef LLVM_TRANSFORMS_IPO_DEADARGUMENTELIMINATION_H 21303231Sdim#define LLVM_TRANSFORMS_IPO_DEADARGUMENTELIMINATION_H 22303231Sdim 23303231Sdim#include "llvm/IR/Module.h" 24303231Sdim#include "llvm/IR/PassManager.h" 25303231Sdim 26303231Sdim#include <map> 27303231Sdim#include <set> 28303231Sdim#include <string> 29303231Sdim 30303231Sdimnamespace llvm { 31303231Sdim 32303231Sdim/// Eliminate dead arguments (and return values) from functions. 33303231Sdimclass DeadArgumentEliminationPass 34303231Sdim : public PassInfoMixin<DeadArgumentEliminationPass> { 35303231Sdimpublic: 36303231Sdim /// Struct that represents (part of) either a return value or a function 37303231Sdim /// argument. Used so that arguments and return values can be used 38303231Sdim /// interchangeably. 39303231Sdim struct RetOrArg { 40303231Sdim RetOrArg(const Function *F, unsigned Idx, bool IsArg) 41303231Sdim : F(F), Idx(Idx), IsArg(IsArg) {} 42303231Sdim const Function *F; 43303231Sdim unsigned Idx; 44303231Sdim bool IsArg; 45303231Sdim 46303231Sdim /// Make RetOrArg comparable, so we can put it into a map. 47303231Sdim bool operator<(const RetOrArg &O) const { 48303231Sdim return std::tie(F, Idx, IsArg) < std::tie(O.F, O.Idx, O.IsArg); 49303231Sdim } 50303231Sdim 51303231Sdim /// Make RetOrArg comparable, so we can easily iterate the multimap. 52303231Sdim bool operator==(const RetOrArg &O) const { 53303231Sdim return F == O.F && Idx == O.Idx && IsArg == O.IsArg; 54303231Sdim } 55303231Sdim 56303231Sdim std::string getDescription() const { 57303231Sdim return (Twine(IsArg ? "Argument #" : "Return value #") + Twine(Idx) + 58303231Sdim " of function " + F->getName()) 59303231Sdim .str(); 60303231Sdim } 61303231Sdim }; 62303231Sdim 63303231Sdim /// Liveness enum - During our initial pass over the program, we determine 64303231Sdim /// that things are either alive or maybe alive. We don't mark anything 65303231Sdim /// explicitly dead (even if we know they are), since anything not alive 66303231Sdim /// with no registered uses (in Uses) will never be marked alive and will 67303231Sdim /// thus become dead in the end. 68303231Sdim enum Liveness { Live, MaybeLive }; 69303231Sdim 70303231Sdim /// Convenience wrapper 71303231Sdim RetOrArg CreateRet(const Function *F, unsigned Idx) { 72303231Sdim return RetOrArg(F, Idx, false); 73303231Sdim } 74303231Sdim /// Convenience wrapper 75303231Sdim RetOrArg CreateArg(const Function *F, unsigned Idx) { 76303231Sdim return RetOrArg(F, Idx, true); 77303231Sdim } 78303231Sdim 79303231Sdim typedef std::multimap<RetOrArg, RetOrArg> UseMap; 80303231Sdim /// This maps a return value or argument to any MaybeLive return values or 81303231Sdim /// arguments it uses. This allows the MaybeLive values to be marked live 82303231Sdim /// when any of its users is marked live. 83303231Sdim /// For example (indices are left out for clarity): 84303231Sdim /// - Uses[ret F] = ret G 85303231Sdim /// This means that F calls G, and F returns the value returned by G. 86303231Sdim /// - Uses[arg F] = ret G 87303231Sdim /// This means that some function calls G and passes its result as an 88303231Sdim /// argument to F. 89303231Sdim /// - Uses[ret F] = arg F 90303231Sdim /// This means that F returns one of its own arguments. 91303231Sdim /// - Uses[arg F] = arg G 92303231Sdim /// This means that G calls F and passes one of its own (G's) arguments 93303231Sdim /// directly to F. 94303231Sdim UseMap Uses; 95303231Sdim 96303231Sdim typedef std::set<RetOrArg> LiveSet; 97303231Sdim typedef std::set<const Function *> LiveFuncSet; 98303231Sdim 99303231Sdim /// This set contains all values that have been determined to be live. 100303231Sdim LiveSet LiveValues; 101303231Sdim /// This set contains all values that are cannot be changed in any way. 102303231Sdim LiveFuncSet LiveFunctions; 103303231Sdim 104303231Sdim typedef SmallVector<RetOrArg, 5> UseVector; 105303231Sdim 106303231Sdim /// This allows this pass to do double-duty as the dead arg hacking pass 107303231Sdim /// (used only by bugpoint). 108303231Sdim bool ShouldHackArguments = false; 109303231Sdim 110303231Sdimpublic: 111303231Sdim DeadArgumentEliminationPass(bool ShouldHackArguments_ = false) 112303231Sdim : ShouldHackArguments(ShouldHackArguments_) {} 113303231Sdim PreservedAnalyses run(Module &M, ModuleAnalysisManager &); 114303231Sdim 115303231Sdimprivate: 116303231Sdim Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); 117303231Sdim Liveness SurveyUse(const Use *U, UseVector &MaybeLiveUses, 118303231Sdim unsigned RetValNum = -1U); 119303231Sdim Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses); 120303231Sdim 121303231Sdim void SurveyFunction(const Function &F); 122303231Sdim void MarkValue(const RetOrArg &RA, Liveness L, 123303231Sdim const UseVector &MaybeLiveUses); 124303231Sdim void MarkLive(const RetOrArg &RA); 125303231Sdim void MarkLive(const Function &F); 126303231Sdim void PropagateLiveness(const RetOrArg &RA); 127303231Sdim bool RemoveDeadStuffFromFunction(Function *F); 128303231Sdim bool DeleteDeadVarargs(Function &Fn); 129303231Sdim bool RemoveDeadArgumentsFromCallers(Function &Fn); 130303231Sdim}; 131303231Sdim} 132303231Sdim 133303231Sdim#endif // LLVM_TRANSFORMS_IPO_DEADARGUMENTELIMINATION_H 134