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