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/DenseSet.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   /// Client supplied callback to control wheter a symbol must be preserved.
38   const std::function<bool(const GlobalValue &)> MustPreserveGV;
39   /// Set of symbols private to the compiler that this pass should not touch.
40   StringSet<> AlwaysPreserved;
41 
42   /// Return false if we're allowed to internalize this GV.
43   bool shouldPreserveGV(const GlobalValue &GV);
44   /// Internalize GV if it is possible to do so, i.e. it is not externally
45   /// visible and is not a member of an externally visible comdat.
46   bool maybeInternalize(GlobalValue &GV,
47                         const DenseSet<const Comdat *> &ExternalComdats);
48   /// If GV is part of a comdat and is externally visible, keep track of its
49   /// comdat so that we don't internalize any of its members.
50   void checkComdatVisibility(GlobalValue &GV,
51                              DenseSet<const Comdat *> &ExternalComdats);
52 
53 public:
54   InternalizePass();
55   InternalizePass(std::function<bool(const GlobalValue &)> MustPreserveGV)
56       : MustPreserveGV(std::move(MustPreserveGV)) {}
57 
58   /// Run the internalizer on \p TheModule, returns true if any changes was
59   /// made.
60   ///
61   /// If the CallGraph \p CG is supplied, it will be updated when
62   /// internalizing a function (by removing any edge from the "external node")
63   bool internalizeModule(Module &TheModule, CallGraph *CG = nullptr);
64 
65   PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
66 };
67 
68 /// Helper function to internalize functions and variables in a Module.
69 inline bool
70 internalizeModule(Module &TheModule,
71                   std::function<bool(const GlobalValue &)> MustPreserveGV,
72                   CallGraph *CG = nullptr) {
73   return InternalizePass(std::move(MustPreserveGV))
74       .internalizeModule(TheModule, CG);
75 }
76 } // end namespace llvm
77 
78 #endif // LLVM_TRANSFORMS_IPO_INTERNALIZE_H
79