1//==-LTOInternalize.cpp - LLVM Link Time Optimizer Internalization Utility -==//
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 file defines a helper to run the internalization part of LTO.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/LTO/legacy/UpdateCompilerUsed.h"
14#include "llvm/Analysis/TargetLibraryInfo.h"
15#include "llvm/CodeGen/TargetLowering.h"
16#include "llvm/CodeGen/TargetSubtargetInfo.h"
17#include "llvm/IR/Mangler.h"
18#include "llvm/Transforms/Utils/ModuleUtils.h"
19#include "llvm/Target/TargetMachine.h"
20
21using namespace llvm;
22
23namespace {
24
25// Helper class that collects AsmUsed and user supplied libcalls.
26class PreserveLibCallsAndAsmUsed {
27public:
28 PreserveLibCallsAndAsmUsed(const StringSet<> &AsmUndefinedRefs,
29 const TargetMachine &TM,
30 std::vector<GlobalValue *> &LLVMUsed)
31 : AsmUndefinedRefs(AsmUndefinedRefs), TM(TM), LLVMUsed(LLVMUsed) {}
32
33 void findInModule(Module &TheModule) {
34 initializeLibCalls(TheModule);
35 for (Function &F : TheModule)
36 findLibCallsAndAsm(GV&: F);
37 for (GlobalVariable &GV : TheModule.globals())
38 findLibCallsAndAsm(GV);
39 for (GlobalAlias &GA : TheModule.aliases())
40 findLibCallsAndAsm(GV&: GA);
41 }
42
43private:
44 // Inputs
45 const StringSet<> &AsmUndefinedRefs;
46 const TargetMachine &TM;
47
48 // Temps
49 llvm::Mangler Mangler;
50 StringSet<> Libcalls;
51
52 // Output
53 std::vector<GlobalValue *> &LLVMUsed;
54
55 // Collect names of runtime library functions. User-defined functions with the
56 // same names are added to llvm.compiler.used to prevent them from being
57 // deleted by optimizations.
58 void initializeLibCalls(const Module &TheModule) {
59 TargetLibraryInfoImpl TLII(Triple(TM.getTargetTriple()));
60 TargetLibraryInfo TLI(TLII);
61
62 // TargetLibraryInfo has info on C runtime library calls on the current
63 // target.
64 for (unsigned I = 0, E = static_cast<unsigned>(LibFunc::NumLibFuncs);
65 I != E; ++I) {
66 LibFunc F = static_cast<LibFunc>(I);
67 if (TLI.has(F))
68 Libcalls.insert(key: TLI.getName(F));
69 }
70
71 SmallPtrSet<const TargetLowering *, 1> TLSet;
72
73 for (const Function &F : TheModule) {
74 const TargetLowering *Lowering =
75 TM.getSubtargetImpl(F)->getTargetLowering();
76
77 if (Lowering && TLSet.insert(Ptr: Lowering).second)
78 // TargetLowering has info on library calls that CodeGen expects to be
79 // available, both from the C runtime and compiler-rt.
80 for (unsigned I = 0, E = static_cast<unsigned>(RTLIB::UNKNOWN_LIBCALL);
81 I != E; ++I)
82 if (const char *Name =
83 Lowering->getLibcallName(Call: static_cast<RTLIB::Libcall>(I)))
84 Libcalls.insert(key: Name);
85 }
86 }
87
88 void findLibCallsAndAsm(GlobalValue &GV) {
89 // There are no restrictions to apply to declarations.
90 if (GV.isDeclaration())
91 return;
92
93 // There is nothing more restrictive than private linkage.
94 if (GV.hasPrivateLinkage())
95 return;
96
97 // Conservatively append user-supplied runtime library functions (supplied
98 // either directly, or via a function alias) to llvm.compiler.used. These
99 // could be internalized and deleted by optimizations like -globalopt,
100 // causing problems when later optimizations add new library calls (e.g.,
101 // llvm.memset => memset and printf => puts).
102 // Leave it to the linker to remove any dead code (e.g. with -dead_strip).
103 GlobalValue *FuncAliasee = nullptr;
104 if (isa<GlobalAlias>(Val: GV)) {
105 auto *A = cast<GlobalAlias>(Val: &GV);
106 FuncAliasee = dyn_cast<Function>(Val: A->getAliasee());
107 }
108 if ((isa<Function>(Val: GV) || FuncAliasee) && Libcalls.count(Key: GV.getName())) {
109 LLVMUsed.push_back(x: &GV);
110 return;
111 }
112
113 SmallString<64> Buffer;
114 TM.getNameWithPrefix(Name&: Buffer, GV: &GV, Mang&: Mangler);
115 if (AsmUndefinedRefs.count(Key: Buffer))
116 LLVMUsed.push_back(x: &GV);
117 }
118};
119
120} // namespace anonymous
121
122void llvm::updateCompilerUsed(Module &TheModule, const TargetMachine &TM,
123 const StringSet<> &AsmUndefinedRefs) {
124 std::vector<GlobalValue *> UsedValues;
125 PreserveLibCallsAndAsmUsed(AsmUndefinedRefs, TM, UsedValues)
126 .findInModule(TheModule);
127
128 if (UsedValues.empty())
129 return;
130
131 appendToCompilerUsed(M&: TheModule, Values: UsedValues);
132}
133

source code of llvm/lib/LTO/UpdateCompilerUsed.cpp