1 //===-lto.cpp - LLVM Link Time Optimizer ----------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Devang Patel and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implementes link time optimization library. This library is
11 // intended to be used by linker to optimize code at link time.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Module.h"
16 #include "llvm/PassManager.h"
17 #include "llvm/Linker.h"
18 #include "llvm/Constants.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/SymbolTable.h"
21 #include "llvm/Bytecode/Reader.h"
22 #include "llvm/Bytecode/Writer.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/FileUtilities.h"
25 #include "llvm/Support/SystemUtils.h"
26 #include "llvm/System/Program.h"
27 #include "llvm/System/Signals.h"
28 #include "llvm/Analysis/Passes.h"
29 #include "llvm/Analysis/Verifier.h"
30 #include "llvm/Target/SubtargetFeature.h"
31 #include "llvm/Target/TargetData.h"
32 #include "llvm/Target/TargetMachine.h"
33 #include "llvm/Target/TargetMachineRegistry.h"
34 #include "llvm/Transforms/IPO.h"
35 #include "llvm/Transforms/Scalar.h"
36 #include "llvm/Analysis/LoadValueNumbering.h"
37 #include "llvm/LinkTimeOptimizer.h"
44 llvm::LinkTimeOptimizer *createLLVMOptimizer()
46 llvm::LinkTimeOptimizer *l = new llvm::LinkTimeOptimizer();
52 /// If symbol is not used then make it internal and let optimizer takes
54 void LLVMSymbol::mayBeNotUsed() {
55 gv->setLinkage(GlobalValue::InternalLinkage);
59 // FIXME : Take advantage of GlobalPrefix from AsmPrinter
60 static const char *addUnderscore(const char *name) {
61 size_t namelen = strlen(name);
62 char *symName = (char*)malloc(namelen+2);
64 strcpy(&symName[1], name);
68 // Map LLVM LinkageType to LTO LinakgeType
69 static LTOLinkageTypes
70 getLTOLinkageType(GlobalValue *v)
73 if (v->hasExternalLinkage())
74 lt = LTOExternalLinkage;
75 else if (v->hasLinkOnceLinkage())
76 lt = LTOLinkOnceLinkage;
77 else if (v->hasWeakLinkage())
80 // Otherwise it is internal linkage for link time optimizer
81 lt = LTOInternalLinkage;
85 // Find exeternal symbols referenced by VALUE. This is a recursive function.
87 findExternalRefs(Value *value, std::set<const char *> &references) {
89 if (ConstantExpr *ce = dyn_cast<ConstantExpr>(value))
90 for (unsigned i = 0, e = ce->getNumOperands(); i != e; ++i)
91 findExternalRefs(ce->getOperand(i), references);
92 else if (GlobalValue *gv = dyn_cast<GlobalValue>(value)) {
93 LTOLinkageTypes lt = getLTOLinkageType(gv);
94 if (lt != LTOInternalLinkage && strncmp (gv->getName().c_str(), "llvm.", 5))
95 references.insert(addUnderscore(gv->getName().c_str()));
99 /// InputFilename is a LLVM bytecode file. Read it using bytecode reader.
100 /// Collect global functions and symbol names in symbols vector.
101 /// Collect external references in references vector.
102 /// Return LTO_READ_SUCCESS if there is no error.
104 LinkTimeOptimizer::readLLVMObjectFile(const std::string &InputFilename,
105 NameToSymbolMap &symbols,
106 std::set<const char *> &references)
108 Module *m = ParseBytecodeFile(InputFilename);
110 return LTO_READ_FAILURE;
112 modules.push_back(m);
114 for (Module::iterator f = m->begin(), e = m->end(); f != e; ++f) {
116 LTOLinkageTypes lt = getLTOLinkageType(f);
118 if (!f->isExternal() && lt != LTOInternalLinkage
119 && strncmp (f->getName().c_str(), "llvm.", 5)) {
120 const char *name = addUnderscore(f->getName().c_str());
121 LLVMSymbol *newSymbol = new LLVMSymbol(lt, f);
122 symbols[name] = newSymbol;
123 allSymbols[name] = newSymbol;
126 // Collect external symbols referenced by this function.
127 for (Function::iterator b = f->begin(), fe = f->end(); b != fe; ++b)
128 for (BasicBlock::iterator i = b->begin(), be = b->end();
130 for (unsigned count = 0, total = i->getNumOperands();
131 count != total; ++count)
132 findExternalRefs(i->getOperand(count), references);
135 for (Module::global_iterator v = m->global_begin(), e = m->global_end();
137 LTOLinkageTypes lt = getLTOLinkageType(v);
138 if (!v->isExternal() && lt != LTOInternalLinkage
139 && strncmp (v->getName().c_str(), "llvm.", 5)) {
140 const char *name = addUnderscore(v->getName().c_str());
141 LLVMSymbol *newSymbol = new LLVMSymbol(lt,v);
142 symbols[name] = newSymbol;
146 return LTO_READ_SUCCESS;
149 /// Optimize module M using various IPO passes. Use exportList to
150 /// internalize selected symbols. Target platform is selected
151 /// based on information available to module M. No new target
152 /// features are selected.
153 static enum LTOStatus lto_optimize(Module *M, std::ostream &Out,
154 std::vector<const char *> &exportList)
156 // Instantiate the pass manager to organize the passes.
159 // Collect Target info
161 const TargetMachineRegistry::Entry* March =
162 TargetMachineRegistry::getClosestStaticTargetForModule(*M, Err);
165 return LTO_NO_TARGET;
168 std::string Features;
169 std::auto_ptr<TargetMachine> target(March->CtorFn(*M, Features));
171 return LTO_NO_TARGET;
173 TargetMachine &Target = *target.get();
175 // Start off with a verification pass.
176 Passes.add(createVerifierPass());
178 // Add an appropriate TargetData instance for this module...
179 Passes.add(new TargetData(*Target.getTargetData()));
181 // Often if the programmer does not specify proper prototypes for the
182 // functions they are calling, they end up calling a vararg version of the
183 // function that does not get a body filled in (the real function has typed
184 // arguments). This pass merges the two functions.
185 Passes.add(createFunctionResolvingPass());
187 // Internalize symbols if export list is nonemty
188 if (!exportList.empty())
189 Passes.add(createInternalizePass(exportList));
191 // Now that we internalized some globals, see if we can hack on them!
192 Passes.add(createGlobalOptimizerPass());
194 // Linking modules together can lead to duplicated global constants, only
195 // keep one copy of each constant...
196 Passes.add(createConstantMergePass());
198 // If the -s command line option was specified, strip the symbols out of the
199 // resulting program to make it smaller. -s is a GLD option that we are
201 Passes.add(createStripSymbolsPass());
203 // Propagate constants at call sites into the functions they call.
204 Passes.add(createIPConstantPropagationPass());
206 // Remove unused arguments from functions...
207 Passes.add(createDeadArgEliminationPass());
209 Passes.add(createFunctionInliningPass()); // Inline small functions
211 Passes.add(createPruneEHPass()); // Remove dead EH info
213 Passes.add(createGlobalDCEPass()); // Remove dead functions
215 // If we didn't decide to inline a function, check to see if we can
216 // transform it to pass arguments by value instead of by reference.
217 Passes.add(createArgumentPromotionPass());
219 // The IPO passes may leave cruft around. Clean up after them.
220 Passes.add(createInstructionCombiningPass());
222 Passes.add(createScalarReplAggregatesPass()); // Break up allocas
224 // Run a few AA driven optimizations here and now, to cleanup the code.
225 Passes.add(createGlobalsModRefPass()); // IP alias analysis
227 Passes.add(createLICMPass()); // Hoist loop invariants
228 Passes.add(createLoadValueNumberingPass()); // GVN for load instrs
229 Passes.add(createGCSEPass()); // Remove common subexprs
230 Passes.add(createDeadStoreEliminationPass()); // Nuke dead stores
232 // Cleanup and simplify the code after the scalar optimizations.
233 Passes.add(createInstructionCombiningPass());
235 // Delete basic blocks, which optimization passes may have killed...
236 Passes.add(createCFGSimplificationPass());
238 // Now that we have optimized the program, discard unreachable functions...
239 Passes.add(createGlobalDCEPass());
241 // Make sure everything is still good.
242 Passes.add(createVerifierPass());
244 Target.addPassesToEmitFile(Passes, Out, TargetMachine::AssemblyFile, true);
246 // Run our queue of passes all at once now, efficiently.
249 return LTO_OPT_SUCCESS;
252 ///Link all modules together and optimize them using IPO. Generate
253 /// native object file using OutputFilename
254 /// Return appropriate LTOStatus.
256 LinkTimeOptimizer::optimizeModules(const std::string &OutputFilename,
257 std::vector<const char *> &exportList)
262 std::ios::openmode io_mode =
263 std::ios::out | std::ios::trunc | std::ios::binary;
264 std::string *errMsg = NULL;
265 Module *bigOne = modules[0];
266 Linker theLinker("LinkTimeOptimizer", bigOne, false);
267 for (unsigned i = 1, e = modules.size(); i != e; ++i)
268 if (theLinker.LinkModules(bigOne, modules[i], errMsg))
269 return LTO_MODULE_MERGE_FAILURE;
272 // Enable this when -save-temps is used
273 std::ofstream Out("big.bc", io_mode);
274 WriteBytecodeToFile(bigOne, Out, true);
277 // Strip leading underscore because it was added to match names
279 for (unsigned i = 0, e = exportList.size(); i != e; ++i) {
280 const char *name = exportList[i];
281 if (strlen(name) > 2 && name[0] == '_')
282 exportList[i] = &name[1];
285 sys::Path tmpAsmFilePath("/tmp/");
286 tmpAsmFilePath.createTemporaryFileOnDisk();
287 sys::RemoveFileOnSignal(tmpAsmFilePath);
289 std::ofstream asmFile(tmpAsmFilePath.c_str(), io_mode);
290 if (!asmFile.is_open() || asmFile.bad()) {
291 if (tmpAsmFilePath.exists())
292 tmpAsmFilePath.eraseFromDisk();
293 return LTO_WRITE_FAILURE;
296 enum LTOStatus status = lto_optimize(bigOne, asmFile, exportList);
298 if (status != LTO_OPT_SUCCESS) {
299 tmpAsmFilePath.eraseFromDisk();
303 // Run GCC to assemble and link the program into native code.
306 // We can't just assemble and link the file with the system assembler
307 // and linker because we don't know where to put the _start symbol.
308 // GCC mysteriously knows how to do it.
309 const sys::Path gcc = FindExecutable("gcc", "/");
311 tmpAsmFilePath.eraseFromDisk();
312 return LTO_ASM_FAILURE;
315 std::vector<const char*> args;
316 args.push_back(gcc.c_str());
317 args.push_back("-c");
318 args.push_back("-x");
319 args.push_back("assembler");
320 args.push_back("-o");
321 args.push_back(OutputFilename.c_str());
322 args.push_back(tmpAsmFilePath.c_str());
325 int R1 = sys::Program::ExecuteAndWait(gcc, &args[0], 0, 0, 1);
327 tmpAsmFilePath.eraseFromDisk();
329 return LTO_OPT_SUCCESS;