lto.cpp revision 0701a2f70df66134ead84d4fe86b20b8f28c4fc3
1//===-lto.cpp - LLVM Link Time Optimizer ----------------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 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. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implementes link time optimization library. This library is 11// intended to be used by linker to optimize code at link time. 12// 13//===----------------------------------------------------------------------===// 14 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/Support/Mangler.h" 27#include "llvm/System/Program.h" 28#include "llvm/System/Signals.h" 29#include "llvm/Analysis/Passes.h" 30#include "llvm/Analysis/Verifier.h" 31#include "llvm/Target/SubtargetFeature.h" 32#include "llvm/Target/TargetData.h" 33#include "llvm/Target/TargetMachine.h" 34#include "llvm/Target/TargetMachineRegistry.h" 35#include "llvm/Transforms/IPO.h" 36#include "llvm/Transforms/Scalar.h" 37#include "llvm/Analysis/LoadValueNumbering.h" 38#include "llvm/LinkTimeOptimizer.h" 39#include <fstream> 40#include <iostream> 41 42using namespace llvm; 43 44extern "C" 45llvm::LinkTimeOptimizer *createLLVMOptimizer() 46{ 47 llvm::LinkTimeOptimizer *l = new llvm::LinkTimeOptimizer(); 48 return l; 49} 50 51 52 53/// If symbol is not used then make it internal and let optimizer takes 54/// care of it. 55void LLVMSymbol::mayBeNotUsed() { 56 gv->setLinkage(GlobalValue::InternalLinkage); 57} 58 59// Helper routine 60// FIXME : Take advantage of GlobalPrefix from AsmPrinter 61static const char *addUnderscore(const char *name) { 62 size_t namelen = strlen(name); 63 char *symName = (char*)malloc(namelen+2); 64 symName[0] = '_'; 65 strcpy(&symName[1], name); 66 return symName; 67} 68 69// Map LLVM LinkageType to LTO LinakgeType 70static LTOLinkageTypes 71getLTOLinkageType(GlobalValue *v) 72{ 73 LTOLinkageTypes lt; 74 if (v->hasExternalLinkage()) 75 lt = LTOExternalLinkage; 76 else if (v->hasLinkOnceLinkage()) 77 lt = LTOLinkOnceLinkage; 78 else if (v->hasWeakLinkage()) 79 lt = LTOWeakLinkage; 80 else 81 // Otherwise it is internal linkage for link time optimizer 82 lt = LTOInternalLinkage; 83 return lt; 84} 85 86// Find exeternal symbols referenced by VALUE. This is a recursive function. 87static void 88findExternalRefs(Value *value, std::set<std::string> &references, 89 Mangler &mangler) { 90 91 if (GlobalValue *gv = dyn_cast<GlobalValue>(value)) { 92 LTOLinkageTypes lt = getLTOLinkageType(gv); 93 if (lt != LTOInternalLinkage && strncmp (gv->getName().c_str(), "llvm.", 5)) 94 references.insert(mangler.getValueName(gv)); 95 } 96 else if (Constant *c = dyn_cast<Constant>(value)) 97 // Handle ConstantExpr, ConstantStruct, ConstantArry etc.. 98 for (unsigned i = 0, e = c->getNumOperands(); i != e; ++i) 99 findExternalRefs(c->getOperand(i), references, mangler); 100} 101 102/// InputFilename is a LLVM bytecode file. If Module with InputFilename is 103/// available then return it. Otherwise parseInputFilename. 104Module * 105LinkTimeOptimizer::getModule(const std::string &InputFilename) 106{ 107 Module *m = NULL; 108 109 NameToModuleMap::iterator pos = allModules.find(InputFilename.c_str()); 110 if (pos != allModules.end()) 111 m = allModules[InputFilename.c_str()]; 112 else { 113 m = ParseBytecodeFile(InputFilename); 114 allModules[InputFilename.c_str()] = m; 115 } 116 return m; 117} 118 119/// InputFilename is a LLVM bytecode file. Read it using bytecode reader. 120/// Collect global functions and symbol names in symbols vector. 121/// Collect external references in references vector. 122/// Return LTO_READ_SUCCESS if there is no error. 123enum LTOStatus 124LinkTimeOptimizer::readLLVMObjectFile(const std::string &InputFilename, 125 NameToSymbolMap &symbols, 126 std::set<std::string> &references) 127{ 128 Module *m = getModule(InputFilename); 129 if (!m) 130 return LTO_READ_FAILURE; 131 132 // Use mangler to add GlobalPrefix to names to match linker names. 133 // FIXME : Instead of hard coding "-" use GlobalPrefix. 134 Mangler mangler(*m, "_"); 135 136 modules.push_back(m); 137 138 for (Module::iterator f = m->begin(), e = m->end(); f != e; ++f) { 139 140 LTOLinkageTypes lt = getLTOLinkageType(f); 141 142 if (!f->isExternal() && lt != LTOInternalLinkage 143 && strncmp (f->getName().c_str(), "llvm.", 5)) { 144 LLVMSymbol *newSymbol = new LLVMSymbol(lt, f, f->getName(), 145 mangler.getValueName(f)); 146 symbols[newSymbol->getMangledName()] = newSymbol; 147 allSymbols[newSymbol->getMangledName()] = newSymbol; 148 } 149 150 // Collect external symbols referenced by this function. 151 for (Function::iterator b = f->begin(), fe = f->end(); b != fe; ++b) 152 for (BasicBlock::iterator i = b->begin(), be = b->end(); 153 i != be; ++i) 154 for (unsigned count = 0, total = i->getNumOperands(); 155 count != total; ++count) 156 findExternalRefs(i->getOperand(count), references, mangler); 157 } 158 159 for (Module::global_iterator v = m->global_begin(), e = m->global_end(); 160 v != e; ++v) { 161 LTOLinkageTypes lt = getLTOLinkageType(v); 162 if (!v->isExternal() && lt != LTOInternalLinkage 163 && strncmp (v->getName().c_str(), "llvm.", 5)) { 164 LLVMSymbol *newSymbol = new LLVMSymbol(lt, v, v->getName(), 165 mangler.getValueName(v)); 166 symbols[newSymbol->getMangledName()] = newSymbol; 167 allSymbols[newSymbol->getMangledName()] = newSymbol; 168 169 for (unsigned count = 0, total = v->getNumOperands(); 170 count != total; ++count) 171 findExternalRefs(v->getOperand(count), references, mangler); 172 173 } 174 } 175 176 return LTO_READ_SUCCESS; 177} 178 179/// Optimize module M using various IPO passes. Use exportList to 180/// internalize selected symbols. Target platform is selected 181/// based on information available to module M. No new target 182/// features are selected. 183static enum LTOStatus lto_optimize(Module *M, std::ostream &Out, 184 std::vector<const char *> &exportList) 185{ 186 // Instantiate the pass manager to organize the passes. 187 PassManager Passes; 188 189 // Collect Target info 190 std::string Err; 191 const TargetMachineRegistry::Entry* March = 192 TargetMachineRegistry::getClosestStaticTargetForModule(*M, Err); 193 194 if (March == 0) 195 return LTO_NO_TARGET; 196 197 // Create target 198 std::string Features; 199 std::auto_ptr<TargetMachine> target(March->CtorFn(*M, Features)); 200 if (!target.get()) 201 return LTO_NO_TARGET; 202 203 TargetMachine &Target = *target.get(); 204 205 // Start off with a verification pass. 206 Passes.add(createVerifierPass()); 207 208 // Add an appropriate TargetData instance for this module... 209 Passes.add(new TargetData(*Target.getTargetData())); 210 211 // Often if the programmer does not specify proper prototypes for the 212 // functions they are calling, they end up calling a vararg version of the 213 // function that does not get a body filled in (the real function has typed 214 // arguments). This pass merges the two functions. 215 Passes.add(createFunctionResolvingPass()); 216 217 // Internalize symbols if export list is nonemty 218 if (!exportList.empty()) 219 Passes.add(createInternalizePass(exportList)); 220 221 // Now that we internalized some globals, see if we can hack on them! 222 Passes.add(createGlobalOptimizerPass()); 223 224 // Linking modules together can lead to duplicated global constants, only 225 // keep one copy of each constant... 226 Passes.add(createConstantMergePass()); 227 228 // If the -s command line option was specified, strip the symbols out of the 229 // resulting program to make it smaller. -s is a GLD option that we are 230 // supporting. 231 Passes.add(createStripSymbolsPass()); 232 233 // Propagate constants at call sites into the functions they call. 234 Passes.add(createIPConstantPropagationPass()); 235 236 // Remove unused arguments from functions... 237 Passes.add(createDeadArgEliminationPass()); 238 239 Passes.add(createFunctionInliningPass()); // Inline small functions 240 241 Passes.add(createPruneEHPass()); // Remove dead EH info 242 243 Passes.add(createGlobalDCEPass()); // Remove dead functions 244 245 // If we didn't decide to inline a function, check to see if we can 246 // transform it to pass arguments by value instead of by reference. 247 Passes.add(createArgumentPromotionPass()); 248 249 // The IPO passes may leave cruft around. Clean up after them. 250 Passes.add(createInstructionCombiningPass()); 251 252 Passes.add(createScalarReplAggregatesPass()); // Break up allocas 253 254 // Run a few AA driven optimizations here and now, to cleanup the code. 255 Passes.add(createGlobalsModRefPass()); // IP alias analysis 256 257 Passes.add(createLICMPass()); // Hoist loop invariants 258 Passes.add(createLoadValueNumberingPass()); // GVN for load instrs 259 Passes.add(createGCSEPass()); // Remove common subexprs 260 Passes.add(createDeadStoreEliminationPass()); // Nuke dead stores 261 262 // Cleanup and simplify the code after the scalar optimizations. 263 Passes.add(createInstructionCombiningPass()); 264 265 // Delete basic blocks, which optimization passes may have killed... 266 Passes.add(createCFGSimplificationPass()); 267 268 // Now that we have optimized the program, discard unreachable functions... 269 Passes.add(createGlobalDCEPass()); 270 271 // Make sure everything is still good. 272 Passes.add(createVerifierPass()); 273 274 Target.addPassesToEmitFile(Passes, Out, TargetMachine::AssemblyFile, true); 275 276 // Run our queue of passes all at once now, efficiently. 277 Passes.run(*M); 278 279 return LTO_OPT_SUCCESS; 280} 281 282///Link all modules together and optimize them using IPO. Generate 283/// native object file using OutputFilename 284/// Return appropriate LTOStatus. 285enum LTOStatus 286LinkTimeOptimizer::optimizeModules(const std::string &OutputFilename, 287 std::vector<const char *> &exportList, 288 std::string &targetTriple) 289{ 290 if (modules.empty()) 291 return LTO_NO_WORK; 292 293 std::ios::openmode io_mode = 294 std::ios::out | std::ios::trunc | std::ios::binary; 295 std::string *errMsg = NULL; 296 Module *bigOne = modules[0]; 297 Linker theLinker("LinkTimeOptimizer", bigOne, false); 298 for (unsigned i = 1, e = modules.size(); i != e; ++i) 299 if (theLinker.LinkModules(bigOne, modules[i], errMsg)) 300 return LTO_MODULE_MERGE_FAILURE; 301 302#if 0 303 // Enable this when -save-temps is used 304 std::ofstream Out("big.bc", io_mode); 305 WriteBytecodeToFile(bigOne, Out, true); 306#endif 307 308 // Strip leading underscore because it was added to match names 309 // seen by linker. 310 for (unsigned i = 0, e = exportList.size(); i != e; ++i) { 311 const char *name = exportList[i]; 312 NameToSymbolMap::iterator itr = allSymbols.find(name); 313 if (itr != allSymbols.end()) 314 exportList[i] = allSymbols[name]->getName(); 315 } 316 317 sys::Path tmpAsmFilePath("/tmp/"); 318 std::string ErrMsg; 319 if (tmpAsmFilePath.createTemporaryFileOnDisk(&ErrMsg)) { 320 std::cerr << "lto: " << ErrMsg << "\n"; 321 return LTO_WRITE_FAILURE; 322 } 323 sys::RemoveFileOnSignal(tmpAsmFilePath); 324 325 std::ofstream asmFile(tmpAsmFilePath.c_str(), io_mode); 326 if (!asmFile.is_open() || asmFile.bad()) { 327 if (tmpAsmFilePath.exists()) 328 tmpAsmFilePath.eraseFromDisk(); 329 return LTO_WRITE_FAILURE; 330 } 331 332 enum LTOStatus status = lto_optimize(bigOne, asmFile, exportList); 333 asmFile.close(); 334 if (status != LTO_OPT_SUCCESS) { 335 tmpAsmFilePath.eraseFromDisk(); 336 return status; 337 } 338 339 targetTriple = bigOne->getTargetTriple(); 340 341 // Run GCC to assemble and link the program into native code. 342 // 343 // Note: 344 // We can't just assemble and link the file with the system assembler 345 // and linker because we don't know where to put the _start symbol. 346 // GCC mysteriously knows how to do it. 347 const sys::Path gcc = FindExecutable("gcc", "/"); 348 if (gcc.isEmpty()) { 349 tmpAsmFilePath.eraseFromDisk(); 350 return LTO_ASM_FAILURE; 351 } 352 353 std::vector<const char*> args; 354 args.push_back(gcc.c_str()); 355 args.push_back("-c"); 356 args.push_back("-x"); 357 args.push_back("assembler"); 358 args.push_back("-o"); 359 args.push_back(OutputFilename.c_str()); 360 args.push_back(tmpAsmFilePath.c_str()); 361 args.push_back(0); 362 363 sys::Program::ExecuteAndWait(gcc, &args[0], 0, 0, 1); 364 365 tmpAsmFilePath.eraseFromDisk(); 366 367 return LTO_OPT_SUCCESS; 368} 369