| //===- DeadArgumentElimination.h - Eliminate Dead Args ----------*- C++ -*-===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // 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 also deletes dead return values in a similar way. |
| // |
| // This pass is often useful as a cleanup pass to run after aggressive |
| // interprocedural passes, which add possibly-dead arguments or return values. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_TRANSFORMS_IPO_DEADARGUMENTELIMINATION_H |
| #define LLVM_TRANSFORMS_IPO_DEADARGUMENTELIMINATION_H |
| |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Twine.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/PassManager.h" |
| #include <map> |
| #include <set> |
| #include <string> |
| #include <tuple> |
| |
| namespace llvm { |
| |
| class Module; |
| class Use; |
| class Value; |
| |
| /// Eliminate dead arguments (and return values) from functions. |
| class DeadArgumentEliminationPass |
| : public PassInfoMixin<DeadArgumentEliminationPass> { |
| public: |
| /// Struct that represents (part of) either a return value or a function |
| /// argument. Used so that arguments and return values can be used |
| /// interchangeably. |
| struct RetOrArg { |
| const Function *F; |
| unsigned Idx; |
| bool IsArg; |
| |
| RetOrArg(const Function *F, unsigned Idx, bool IsArg) |
| : F(F), Idx(Idx), IsArg(IsArg) {} |
| |
| /// Make RetOrArg comparable, so we can put it into a map. |
| bool operator<(const RetOrArg &O) const { |
| return std::tie(F, Idx, IsArg) < std::tie(O.F, O.Idx, O.IsArg); |
| } |
| |
| /// Make RetOrArg comparable, so we can easily iterate the multimap. |
| bool operator==(const RetOrArg &O) const { |
| return F == O.F && Idx == O.Idx && IsArg == O.IsArg; |
| } |
| |
| std::string getDescription() const { |
| return (Twine(IsArg ? "Argument #" : "Return value #") + Twine(Idx) + |
| " of function " + F->getName()) |
| .str(); |
| } |
| }; |
| |
| /// Liveness enum - During our initial pass over the program, we determine |
| /// that things are either alive or maybe alive. We don't mark anything |
| /// explicitly dead (even if we know they are), since anything not alive |
| /// with no registered uses (in Uses) will never be marked alive and will |
| /// thus become dead in the end. |
| enum Liveness { Live, MaybeLive }; |
| |
| DeadArgumentEliminationPass(bool ShouldHackArguments_ = false) |
| : ShouldHackArguments(ShouldHackArguments_) {} |
| |
| PreservedAnalyses run(Module &M, ModuleAnalysisManager &); |
| |
| /// Convenience wrapper |
| RetOrArg CreateRet(const Function *F, unsigned Idx) { |
| return RetOrArg(F, Idx, false); |
| } |
| |
| /// Convenience wrapper |
| RetOrArg CreateArg(const Function *F, unsigned Idx) { |
| return RetOrArg(F, Idx, true); |
| } |
| |
| using UseMap = std::multimap<RetOrArg, RetOrArg>; |
| |
| /// This maps a return value or argument to any MaybeLive return values or |
| /// arguments it uses. This allows the MaybeLive values to be marked live |
| /// when any of its users is marked live. |
| /// For example (indices are left out for clarity): |
| /// - Uses[ret F] = ret G |
| /// This means that F calls G, and F returns the value returned by G. |
| /// - Uses[arg F] = ret G |
| /// This means that some function calls G and passes its result as an |
| /// argument to F. |
| /// - Uses[ret F] = arg F |
| /// This means that F returns one of its own arguments. |
| /// - Uses[arg F] = arg G |
| /// This means that G calls F and passes one of its own (G's) arguments |
| /// directly to F. |
| UseMap Uses; |
| |
| using LiveSet = std::set<RetOrArg>; |
| using LiveFuncSet = std::set<const Function *>; |
| |
| /// This set contains all values that have been determined to be live. |
| LiveSet LiveValues; |
| |
| /// This set contains all values that are cannot be changed in any way. |
| LiveFuncSet LiveFunctions; |
| |
| using UseVector = SmallVector<RetOrArg, 5>; |
| |
| /// This allows this pass to do double-duty as the dead arg hacking pass |
| /// (used only by bugpoint). |
| bool ShouldHackArguments = false; |
| |
| private: |
| Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses); |
| Liveness SurveyUse(const Use *U, UseVector &MaybeLiveUses, |
| unsigned RetValNum = -1U); |
| Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses); |
| |
| void SurveyFunction(const Function &F); |
| void MarkValue(const RetOrArg &RA, Liveness L, |
| const UseVector &MaybeLiveUses); |
| void MarkLive(const RetOrArg &RA); |
| void MarkLive(const Function &F); |
| void PropagateLiveness(const RetOrArg &RA); |
| bool RemoveDeadStuffFromFunction(Function *F); |
| bool DeleteDeadVarargs(Function &Fn); |
| bool RemoveDeadArgumentsFromCallers(Function &Fn); |
| }; |
| |
| } // end namespace llvm |
| |
| #endif // LLVM_TRANSFORMS_IPO_DEADARGUMENTELIMINATION_H |