LCOV - code coverage report
Current view: top level - include/llvm/Transforms/IPO - DeadArgumentElimination.h (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 4 4 100.0 %
Date: 2018-02-23 15:42:53 Functions: 2 2 100.0 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===- DeadArgumentElimination.h - Eliminate Dead Args ----------*- C++ -*-===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : //
      10             : // This pass deletes dead arguments from internal functions.  Dead argument
      11             : // elimination removes arguments which are directly dead, as well as arguments
      12             : // only passed into function calls as dead arguments of other functions.  This
      13             : // pass also deletes dead return values in a similar way.
      14             : //
      15             : // This pass is often useful as a cleanup pass to run after aggressive
      16             : // interprocedural passes, which add possibly-dead arguments or return values.
      17             : //
      18             : //===----------------------------------------------------------------------===//
      19             : 
      20             : #ifndef LLVM_TRANSFORMS_IPO_DEADARGUMENTELIMINATION_H
      21             : #define LLVM_TRANSFORMS_IPO_DEADARGUMENTELIMINATION_H
      22             : 
      23             : #include "llvm/ADT/SmallVector.h"
      24             : #include "llvm/ADT/Twine.h"
      25             : #include "llvm/IR/Function.h"
      26             : #include "llvm/IR/PassManager.h"
      27             : #include <map>
      28             : #include <set>
      29             : #include <string>
      30             : #include <tuple>
      31             : 
      32             : namespace llvm {
      33             : 
      34             : class Module;
      35             : class Use;
      36             : class Value;
      37             : 
      38             : /// Eliminate dead arguments (and return values) from functions.
      39        3388 : class DeadArgumentEliminationPass
      40             :     : public PassInfoMixin<DeadArgumentEliminationPass> {
      41             : public:
      42             :   /// Struct that represents (part of) either a return value or a function
      43             :   /// argument.  Used so that arguments and return values can be used
      44             :   /// interchangeably.
      45             :   struct RetOrArg {
      46             :     const Function *F;
      47             :     unsigned Idx;
      48             :     bool IsArg;
      49             : 
      50             :     RetOrArg(const Function *F, unsigned Idx, bool IsArg)
      51             :         : F(F), Idx(Idx), IsArg(IsArg) {}
      52             : 
      53             :     /// Make RetOrArg comparable, so we can put it into a map.
      54             :     bool operator<(const RetOrArg &O) const {
      55      949588 :       return std::tie(F, Idx, IsArg) < std::tie(O.F, O.Idx, O.IsArg);
      56             :     }
      57             : 
      58             :     /// Make RetOrArg comparable, so we can easily iterate the multimap.
      59             :     bool operator==(const RetOrArg &O) const {
      60       24064 :       return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
      61             :     }
      62             : 
      63             :     std::string getDescription() const {
      64             :       return (Twine(IsArg ? "Argument #" : "Return value #") + Twine(Idx) +
      65             :               " of function " + F->getName())
      66             :           .str();
      67             :     }
      68             :   };
      69             : 
      70             :   /// Liveness enum - During our initial pass over the program, we determine
      71             :   /// that things are either alive or maybe alive. We don't mark anything
      72             :   /// explicitly dead (even if we know they are), since anything not alive
      73             :   /// with no registered uses (in Uses) will never be marked alive and will
      74             :   /// thus become dead in the end.
      75             :   enum Liveness { Live, MaybeLive };
      76             : 
      77             :   DeadArgumentEliminationPass(bool ShouldHackArguments_ = false)
      78        2828 :       : ShouldHackArguments(ShouldHackArguments_) {}
      79             : 
      80             :   PreservedAnalyses run(Module &M, ModuleAnalysisManager &);
      81             : 
      82             :   /// Convenience wrapper
      83             :   RetOrArg CreateRet(const Function *F, unsigned Idx) {
      84             :     return RetOrArg(F, Idx, false);
      85             :   }
      86             : 
      87             :   /// Convenience wrapper
      88             :   RetOrArg CreateArg(const Function *F, unsigned Idx) {
      89             :     return RetOrArg(F, Idx, true);
      90             :   }
      91             : 
      92             :   using UseMap = std::multimap<RetOrArg, RetOrArg>;
      93             : 
      94             :   /// This maps a return value or argument to any MaybeLive return values or
      95             :   /// arguments it uses. This allows the MaybeLive values to be marked live
      96             :   /// when any of its users is marked live.
      97             :   /// For example (indices are left out for clarity):
      98             :   ///  - Uses[ret F] = ret G
      99             :   ///    This means that F calls G, and F returns the value returned by G.
     100             :   ///  - Uses[arg F] = ret G
     101             :   ///    This means that some function calls G and passes its result as an
     102             :   ///    argument to F.
     103             :   ///  - Uses[ret F] = arg F
     104             :   ///    This means that F returns one of its own arguments.
     105             :   ///  - Uses[arg F] = arg G
     106             :   ///    This means that G calls F and passes one of its own (G's) arguments
     107             :   ///    directly to F.
     108             :   UseMap Uses;
     109             : 
     110             :   using LiveSet = std::set<RetOrArg>;
     111             :   using LiveFuncSet = std::set<const Function *>;
     112             : 
     113             :   /// This set contains all values that have been determined to be live.
     114             :   LiveSet LiveValues;
     115             : 
     116             :   /// This set contains all values that are cannot be changed in any way.
     117             :   LiveFuncSet LiveFunctions;
     118             : 
     119             :   using UseVector = SmallVector<RetOrArg, 5>;
     120             : 
     121             :   /// This allows this pass to do double-duty as the dead arg hacking pass
     122             :   /// (used only by bugpoint).
     123             :   bool ShouldHackArguments = false;
     124             : 
     125             : private:
     126             :   Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
     127             :   Liveness SurveyUse(const Use *U, UseVector &MaybeLiveUses,
     128             :                      unsigned RetValNum = -1U);
     129             :   Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses);
     130             : 
     131             :   void SurveyFunction(const Function &F);
     132             :   void MarkValue(const RetOrArg &RA, Liveness L,
     133             :                  const UseVector &MaybeLiveUses);
     134             :   void MarkLive(const RetOrArg &RA);
     135             :   void MarkLive(const Function &F);
     136             :   void PropagateLiveness(const RetOrArg &RA);
     137             :   bool RemoveDeadStuffFromFunction(Function *F);
     138             :   bool DeleteDeadVarargs(Function &Fn);
     139             :   bool RemoveDeadArgumentsFromCallers(Function &Fn);
     140             : };
     141             : 
     142             : } // end namespace llvm
     143             : 
     144             : #endif // LLVM_TRANSFORMS_IPO_DEADARGUMENTELIMINATION_H

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