1 //====- Internalize.h - Internalization API ---------------------*- C++ -*-===//
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 pass loops over all of the functions and variables in the input module.
10 // If the function or variable does not need to be preserved according to the
11 // client supplied callback, it is marked as internal.
12 //
13 // This transformation would not be legal in a regular compilation, but it gets
14 // extra information from the linker about what is safe.
15 //
16 // For example: Internalizing a function with external linkage. Only if we are
17 // told it is only used from within this module, it is safe to do it.
18 //
19 //===----------------------------------------------------------------------===//
20 
21 #ifndef LLVM_TRANSFORMS_IPO_INTERNALIZE_H
22 #define LLVM_TRANSFORMS_IPO_INTERNALIZE_H
23 
24 #include "llvm/ADT/DenseMap.h"
25 #include "llvm/ADT/StringSet.h"
26 #include "llvm/IR/GlobalValue.h"
27 #include "llvm/IR/PassManager.h"
28 #include <functional>
29 
30 namespace llvm {
31 class Module;
32 class CallGraph;
33 
34 /// A pass that internalizes all functions and variables other than those that
35 /// must be preserved according to \c MustPreserveGV.
36 class InternalizePass : public PassInfoMixin<InternalizePass> {
37   struct ComdatInfo {
38     // The number of members. A comdat with one member which is not externally
39     // visible can be freely dropped.
40     size_t Size = 0;
41     // Whether the comdat has an externally visible member.
42     bool External = false;
43   };
44 
45   bool IsWasm = false;
46 
47   /// Client supplied callback to control wheter a symbol must be preserved.
48   const std::function<bool(const GlobalValue &)> MustPreserveGV;
49   /// Set of symbols private to the compiler that this pass should not touch.
50   StringSet<> AlwaysPreserved;
51 
52   /// Return false if we're allowed to internalize this GV.
53   bool shouldPreserveGV(const GlobalValue &GV);
54   /// Internalize GV if it is possible to do so, i.e. it is not externally
55   /// visible and is not a member of an externally visible comdat.
56   bool maybeInternalize(GlobalValue &GV,
57                         DenseMap<const Comdat *, ComdatInfo> &ComdatMap);
58   /// If GV is part of a comdat and is externally visible, keep track of its
59   /// comdat so that we don't internalize any of its members.
60   void checkComdat(GlobalValue &GV,
61                    DenseMap<const Comdat *, ComdatInfo> &ComdatMap);
62 
63 public:
64   InternalizePass();
65   InternalizePass(std::function<bool(const GlobalValue &)> MustPreserveGV)
66       : MustPreserveGV(std::move(MustPreserveGV)) {}
67 
68   /// Run the internalizer on \p TheModule, returns true if any changes was
69   /// made.
70   ///
71   /// If the CallGraph \p CG is supplied, it will be updated when
72   /// internalizing a function (by removing any edge from the "external node")
73   bool internalizeModule(Module &TheModule, CallGraph *CG = nullptr);
74 
75   PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
76 };
77 
78 /// Helper function to internalize functions and variables in a Module.
79 inline bool
80 internalizeModule(Module &TheModule,
81                   std::function<bool(const GlobalValue &)> MustPreserveGV,
82                   CallGraph *CG = nullptr) {
83   return InternalizePass(std::move(MustPreserveGV))
84       .internalizeModule(TheModule, CG);
85 }
86 } // end namespace llvm
87 
88 #endif // LLVM_TRANSFORMS_IPO_INTERNALIZE_H
89