1 //===-- Internalize.cpp - Mark functions internal -------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass loops over all of the functions and variables in the input module.
11 // If the function or variable is not in the list of external names given to
12 // the pass it is marked as internal.
14 // This transformation would not be legal in a regular compilation, but it gets
15 // extra information from the linker about what is safe.
17 // For example: Internalizing a function with external linkage. Only if we are
18 // told it is only used from within this module, it is safe to do it.
20 //===----------------------------------------------------------------------===//
22 #include "llvm/Transforms/IPO.h"
23 #include "llvm/ADT/SmallPtrSet.h"
24 #include "llvm/ADT/Statistic.h"
25 #include "llvm/Analysis/CallGraph.h"
26 #include "llvm/IR/Module.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Support/CommandLine.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/Transforms/Utils/GlobalStatus.h"
32 #include "llvm/Transforms/Utils/ModuleUtils.h"
37 #define DEBUG_TYPE "internalize"
39 STATISTIC(NumAliases , "Number of aliases internalized");
40 STATISTIC(NumFunctions, "Number of functions internalized");
41 STATISTIC(NumGlobals , "Number of global vars internalized");
43 // APIFile - A file which contains a list of symbols that should not be marked
45 static cl::opt<std::string>
46 APIFile("internalize-public-api-file", cl::value_desc("filename"),
47 cl::desc("A file containing list of symbol names to preserve"));
49 // APIList - A list of symbols that should not be marked internal.
50 static cl::list<std::string>
51 APIList("internalize-public-api-list", cl::value_desc("list"),
52 cl::desc("A list of symbol names to preserve"),
56 class InternalizePass : public ModulePass {
57 std::set<std::string> ExternalNames;
59 static char ID; // Pass identification, replacement for typeid
60 explicit InternalizePass();
61 explicit InternalizePass(ArrayRef<const char *> ExportList);
62 void LoadFile(const char *Filename);
63 bool maybeInternalize(GlobalValue &GV,
64 const std::set<const Comdat *> &ExternalComdats);
65 void checkComdatVisibility(GlobalValue &GV,
66 std::set<const Comdat *> &ExternalComdats);
67 bool runOnModule(Module &M) override;
69 void getAnalysisUsage(AnalysisUsage &AU) const override {
71 AU.addPreserved<CallGraphWrapperPass>();
74 } // end anonymous namespace
76 char InternalizePass::ID = 0;
77 INITIALIZE_PASS(InternalizePass, "internalize",
78 "Internalize Global Symbols", false, false)
80 InternalizePass::InternalizePass() : ModulePass(ID) {
81 initializeInternalizePassPass(*PassRegistry::getPassRegistry());
82 if (!APIFile.empty()) // If a filename is specified, use it.
83 LoadFile(APIFile.c_str());
84 ExternalNames.insert(APIList.begin(), APIList.end());
87 InternalizePass::InternalizePass(ArrayRef<const char *> ExportList)
89 initializeInternalizePassPass(*PassRegistry::getPassRegistry());
90 for(ArrayRef<const char *>::const_iterator itr = ExportList.begin();
91 itr != ExportList.end(); itr++) {
92 ExternalNames.insert(*itr);
96 void InternalizePass::LoadFile(const char *Filename) {
97 // Load the APIFile...
98 std::ifstream In(Filename);
100 errs() << "WARNING: Internalize couldn't load file '" << Filename
101 << "'! Continuing as if it's empty.\n";
102 return; // Just continue as if the file were empty
108 ExternalNames.insert(Symbol);
112 static bool isExternallyVisible(const GlobalValue &GV,
113 const std::set<std::string> &ExternalNames) {
114 // Function must be defined here
115 if (GV.isDeclaration())
118 // Available externally is really just a "declaration with a body".
119 if (GV.hasAvailableExternallyLinkage())
122 // Assume that dllexported symbols are referenced elsewhere
123 if (GV.hasDLLExportStorageClass())
126 // Marked to keep external?
127 if (!GV.hasLocalLinkage() && ExternalNames.count(GV.getName()))
133 // Internalize GV if it is possible to do so, i.e. it is not externally visible
134 // and is not a member of an externally visible comdat.
135 bool InternalizePass::maybeInternalize(
136 GlobalValue &GV, const std::set<const Comdat *> &ExternalComdats) {
137 if (Comdat *C = GV.getComdat()) {
138 if (ExternalComdats.count(C))
141 // If a comdat is not externally visible we can drop it.
142 if (auto GO = dyn_cast<GlobalObject>(&GV))
143 GO->setComdat(nullptr);
145 if (GV.hasLocalLinkage())
148 if (GV.hasLocalLinkage())
151 if (isExternallyVisible(GV, ExternalNames))
155 GV.setVisibility(GlobalValue::DefaultVisibility);
156 GV.setLinkage(GlobalValue::InternalLinkage);
160 // If GV is part of a comdat and is externally visible, keep track of its
161 // comdat so that we don't internalize any of its members.
162 void InternalizePass::checkComdatVisibility(
163 GlobalValue &GV, std::set<const Comdat *> &ExternalComdats) {
164 Comdat *C = GV.getComdat();
168 if (isExternallyVisible(GV, ExternalNames))
169 ExternalComdats.insert(C);
172 bool InternalizePass::runOnModule(Module &M) {
173 CallGraphWrapperPass *CGPass = getAnalysisIfAvailable<CallGraphWrapperPass>();
174 CallGraph *CG = CGPass ? &CGPass->getCallGraph() : nullptr;
175 CallGraphNode *ExternalNode = CG ? CG->getExternalCallingNode() : nullptr;
177 SmallPtrSet<GlobalValue *, 8> Used;
178 collectUsedGlobalVariables(M, Used, false);
180 // Collect comdat visiblity information for the module.
181 std::set<const Comdat *> ExternalComdats;
182 if (!M.getComdatSymbolTable().empty()) {
183 for (Function &F : M)
184 checkComdatVisibility(F, ExternalComdats);
185 for (GlobalVariable &GV : M.globals())
186 checkComdatVisibility(GV, ExternalComdats);
187 for (GlobalAlias &GA : M.aliases())
188 checkComdatVisibility(GA, ExternalComdats);
191 // We must assume that globals in llvm.used have a reference that not even
192 // the linker can see, so we don't internalize them.
193 // For llvm.compiler.used the situation is a bit fuzzy. The assembler and
194 // linker can drop those symbols. If this pass is running as part of LTO,
195 // one might think that it could just drop llvm.compiler.used. The problem
196 // is that even in LTO llvm doesn't see every reference. For example,
197 // we don't see references from function local inline assembly. To be
198 // conservative, we internalize symbols in llvm.compiler.used, but we
199 // keep llvm.compiler.used so that the symbol is not deleted by llvm.
200 for (GlobalValue *V : Used) {
201 ExternalNames.insert(V->getName());
204 // Mark all functions not in the api as internal.
205 for (Function &I : M) {
206 if (!maybeInternalize(I, ExternalComdats))
210 // Remove a callgraph edge from the external node to this function.
211 ExternalNode->removeOneAbstractEdgeTo((*CG)[&I]);
214 DEBUG(dbgs() << "Internalizing func " << I.getName() << "\n");
217 // Never internalize the llvm.used symbol. It is used to implement
218 // attribute((used)).
219 // FIXME: Shouldn't this just filter on llvm.metadata section??
220 ExternalNames.insert("llvm.used");
221 ExternalNames.insert("llvm.compiler.used");
223 // Never internalize anchors used by the machine module info, else the info
224 // won't find them. (see MachineModuleInfo.)
225 ExternalNames.insert("llvm.global_ctors");
226 ExternalNames.insert("llvm.global_dtors");
227 ExternalNames.insert("llvm.global.annotations");
229 // Never internalize symbols code-gen inserts.
230 // FIXME: We should probably add this (and the __stack_chk_guard) via some
231 // type of call-back in CodeGen.
232 ExternalNames.insert("__stack_chk_fail");
233 ExternalNames.insert("__stack_chk_guard");
235 // Mark all global variables with initializers that are not in the api as
237 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
239 if (!maybeInternalize(*I, ExternalComdats))
243 DEBUG(dbgs() << "Internalized gvar " << I->getName() << "\n");
246 // Mark all aliases that are not in the api as internal as well.
247 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
249 if (!maybeInternalize(*I, ExternalComdats))
253 DEBUG(dbgs() << "Internalized alias " << I->getName() << "\n");
256 // We do not keep track of whether this pass changed the module because
257 // it adds unnecessary complexity:
258 // 1) This pass will generally be near the start of the pass pipeline, so
259 // there will be no analyses to invalidate.
260 // 2) This pass will most likely end up changing the module and it isn't worth
261 // worrying about optimizing the case where the module is unchanged.
265 ModulePass *llvm::createInternalizePass() { return new InternalizePass(); }
267 ModulePass *llvm::createInternalizePass(ArrayRef<const char *> ExportList) {
268 return new InternalizePass(ExportList);