include/llvm/Transforms/IPO/GlobalDCE.h

   1 //===-- GlobalDCE.h - DCE unreachable internal functions ------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This transform is designed to eliminate unreachable internal globals from the
  10 // program.  It uses an aggressive algorithm, searching out globals that are
  11 // known to be alive.  After it finds all of the globals which are needed, it
  12 // deletes whatever is left over.  This allows it to delete recursive chunks of
  13 // the program which are unreachable.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #ifndef LLVM_TRANSFORMS_IPO_GLOBALDCE_H
  18 #define LLVM_TRANSFORMS_IPO_GLOBALDCE_H
  19
  20 #include "llvm/ADT/DenseMap.h"
  21 #include "llvm/ADT/SmallSet.h"
  22 #include "llvm/IR/Module.h"
  23 #include "llvm/IR/PassManager.h"
  24 #include <unordered_map>
  25
  26 namespace llvm {
  27
  28 /// Pass to remove unused function declarations.
  29 class GlobalDCEPass : public PassInfoMixin<GlobalDCEPass> {
  30 public:
  31   PreservedAnalyses run(Module &M, ModuleAnalysisManager &);
  32
  33 private:
  34   SmallPtrSet<GlobalValue*, 32> AliveGlobals;
  35
  36   /// Global -> Global that uses this global.
  37   DenseMap<GlobalValue *, SmallPtrSet<GlobalValue *, 4>> GVDependencies;
  38
  39   /// Constant -> Globals that use this global cache.
  40   std::unordered_map<Constant *, SmallPtrSet<GlobalValue *, 8>>
  41       ConstantDependenciesCache;
  42
  43   /// Comdat -> Globals in that Comdat section.
  44   std::unordered_multimap<Comdat *, GlobalValue *> ComdatMembers;
  45
  46   /// !type metadata -> set of (vtable, offset) pairs
  47   DenseMap<Metadata *, SmallSet<std::pair<GlobalVariable *, uint64_t>, 4>>
  48       TypeIdMap;
  49
  50   // Global variables which are vtables, and which we have enough information
  51   // about to safely do dead virtual function elimination.
  52   SmallPtrSet<GlobalValue *, 32> VFESafeVTables;
  53
  54   void UpdateGVDependencies(GlobalValue &GV);
  55   void MarkLive(GlobalValue &GV,
  56                 SmallVectorImpl<GlobalValue *> *Updates = nullptr);
  57   bool RemoveUnusedGlobalValue(GlobalValue &GV);
  58
  59   // Dead virtual function elimination.
  60   void AddVirtualFunctionDependencies(Module &M);
  61   void ScanVTables(Module &M);
  62   void ScanTypeCheckedLoadIntrinsics(Module &M);
  63   void ScanVTableLoad(Function *Caller, Metadata *TypeId, uint64_t CallOffset);
  64
  65   void ComputeDependencies(Value *V, SmallPtrSetImpl<GlobalValue *> &U);
  66 };
  67
  68 }
  69
  70 #endif // LLVM_TRANSFORMS_IPO_GLOBALDCE_H