lto.cpp revision 304d5f2edc954a3ef9904ea6d8f9421f40c9abe4
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/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" 38#include <fstream> 39#include <iostream> 40 41using namespace llvm; 42 43extern "C" 44llvm::LinkTimeOptimizer *createLLVMOptimizer() 45{ 46 llvm::LinkTimeOptimizer *l = new llvm::LinkTimeOptimizer(); 47 return l; 48} 49 50 51 52/// If symbol is not used then make it internal and let optimizer takes 53/// care of it. 54void LLVMSymbol::mayBeNotUsed() { 55 gv->setLinkage(GlobalValue::InternalLinkage); 56} 57 58// Helper routine 59// FIXME : Take advantage of GlobalPrefix from AsmPrinter 60static const char *addUnderscore(const char *name) { 61 size_t namelen = strlen(name); 62 char *symName = (char*)malloc(namelen+2); 63 symName[0] = '_'; 64 strcpy(&symName[1], name); 65 return symName; 66} 67 68// Map LLVM LinkageType to LTO LinakgeType 69static LTOLinkageTypes 70getLTOLinkageType(GlobalValue *v) 71{ 72 LTOLinkageTypes lt; 73 if (v->hasExternalLinkage()) 74 lt = LTOExternalLinkage; 75 else if (v->hasLinkOnceLinkage()) 76 lt = LTOLinkOnceLinkage; 77 else if (v->hasWeakLinkage()) 78 lt = LTOWeakLinkage; 79 else 80 // Otherwise it is internal linkage for link time optimizer 81 lt = LTOInternalLinkage; 82 return lt; 83} 84 85// Find exeternal symbols referenced by VALUE. This is a recursive function. 86static void 87findExternalRefs(Value *value, std::set<const char *> &references) { 88 89 if (GlobalValue *gv = dyn_cast<GlobalValue>(value)) { 90 LTOLinkageTypes lt = getLTOLinkageType(gv); 91 if (lt != LTOInternalLinkage && strncmp (gv->getName().c_str(), "llvm.", 5)) 92 references.insert(addUnderscore(gv->getName().c_str())); 93 } 94 else if (Constant *c = dyn_cast<Constant>(value)) 95 // Handle ConstantExpr, ConstantStruct, ConstantArry etc.. 96 for (unsigned i = 0, e = c->getNumOperands(); i != e; ++i) 97 findExternalRefs(c->getOperand(i), references); 98} 99 100/// InputFilename is a LLVM bytecode file. Read it using bytecode reader. 101/// Collect global functions and symbol names in symbols vector. 102/// Collect external references in references vector. 103/// Return LTO_READ_SUCCESS if there is no error. 104enum LTOStatus 105LinkTimeOptimizer::readLLVMObjectFile(const std::string &InputFilename, 106 NameToSymbolMap &symbols, 107 std::set<const char *> &references) 108{ 109 Module *m = ParseBytecodeFile(InputFilename); 110 if (!m) 111 return LTO_READ_FAILURE; 112 113 modules.push_back(m); 114 115 for (Module::iterator f = m->begin(), e = m->end(); f != e; ++f) { 116 117 LTOLinkageTypes lt = getLTOLinkageType(f); 118 119 if (!f->isExternal() && lt != LTOInternalLinkage 120 && strncmp (f->getName().c_str(), "llvm.", 5)) { 121 const char *name = addUnderscore(f->getName().c_str()); 122 LLVMSymbol *newSymbol = new LLVMSymbol(lt, f); 123 symbols[name] = newSymbol; 124 allSymbols[name] = newSymbol; 125 } 126 127 // Collect external symbols referenced by this function. 128 for (Function::iterator b = f->begin(), fe = f->end(); b != fe; ++b) 129 for (BasicBlock::iterator i = b->begin(), be = b->end(); 130 i != be; ++i) 131 for (unsigned count = 0, total = i->getNumOperands(); 132 count != total; ++count) 133 findExternalRefs(i->getOperand(count), references); 134 } 135 136 for (Module::global_iterator v = m->global_begin(), e = m->global_end(); 137 v != e; ++v) { 138 LTOLinkageTypes lt = getLTOLinkageType(v); 139 if (!v->isExternal() && lt != LTOInternalLinkage 140 && strncmp (v->getName().c_str(), "llvm.", 5)) { 141 const char *name = addUnderscore(v->getName().c_str()); 142 LLVMSymbol *newSymbol = new LLVMSymbol(lt,v); 143 symbols[name] = newSymbol; 144 145 for (unsigned count = 0, total = v->getNumOperands(); 146 count != total; ++count) 147 findExternalRefs(v->getOperand(count), references); 148 149 } 150 } 151 152 return LTO_READ_SUCCESS; 153} 154 155/// Optimize module M using various IPO passes. Use exportList to 156/// internalize selected symbols. Target platform is selected 157/// based on information available to module M. No new target 158/// features are selected. 159static enum LTOStatus lto_optimize(Module *M, std::ostream &Out, 160 std::vector<const char *> &exportList) 161{ 162 // Instantiate the pass manager to organize the passes. 163 PassManager Passes; 164 165 // Collect Target info 166 std::string Err; 167 const TargetMachineRegistry::Entry* March = 168 TargetMachineRegistry::getClosestStaticTargetForModule(*M, Err); 169 170 if (March == 0) 171 return LTO_NO_TARGET; 172 173 // Create target 174 std::string Features; 175 std::auto_ptr<TargetMachine> target(March->CtorFn(*M, Features)); 176 if (!target.get()) 177 return LTO_NO_TARGET; 178 179 TargetMachine &Target = *target.get(); 180 181 // Start off with a verification pass. 182 Passes.add(createVerifierPass()); 183 184 // Add an appropriate TargetData instance for this module... 185 Passes.add(new TargetData(*Target.getTargetData())); 186 187 // Often if the programmer does not specify proper prototypes for the 188 // functions they are calling, they end up calling a vararg version of the 189 // function that does not get a body filled in (the real function has typed 190 // arguments). This pass merges the two functions. 191 Passes.add(createFunctionResolvingPass()); 192 193 // Internalize symbols if export list is nonemty 194 if (!exportList.empty()) 195 Passes.add(createInternalizePass(exportList)); 196 197 // Now that we internalized some globals, see if we can hack on them! 198 Passes.add(createGlobalOptimizerPass()); 199 200 // Linking modules together can lead to duplicated global constants, only 201 // keep one copy of each constant... 202 Passes.add(createConstantMergePass()); 203 204 // If the -s command line option was specified, strip the symbols out of the 205 // resulting program to make it smaller. -s is a GLD option that we are 206 // supporting. 207 Passes.add(createStripSymbolsPass()); 208 209 // Propagate constants at call sites into the functions they call. 210 Passes.add(createIPConstantPropagationPass()); 211 212 // Remove unused arguments from functions... 213 Passes.add(createDeadArgEliminationPass()); 214 215 Passes.add(createFunctionInliningPass()); // Inline small functions 216 217 Passes.add(createPruneEHPass()); // Remove dead EH info 218 219 Passes.add(createGlobalDCEPass()); // Remove dead functions 220 221 // If we didn't decide to inline a function, check to see if we can 222 // transform it to pass arguments by value instead of by reference. 223 Passes.add(createArgumentPromotionPass()); 224 225 // The IPO passes may leave cruft around. Clean up after them. 226 Passes.add(createInstructionCombiningPass()); 227 228 Passes.add(createScalarReplAggregatesPass()); // Break up allocas 229 230 // Run a few AA driven optimizations here and now, to cleanup the code. 231 Passes.add(createGlobalsModRefPass()); // IP alias analysis 232 233 Passes.add(createLICMPass()); // Hoist loop invariants 234 Passes.add(createLoadValueNumberingPass()); // GVN for load instrs 235 Passes.add(createGCSEPass()); // Remove common subexprs 236 Passes.add(createDeadStoreEliminationPass()); // Nuke dead stores 237 238 // Cleanup and simplify the code after the scalar optimizations. 239 Passes.add(createInstructionCombiningPass()); 240 241 // Delete basic blocks, which optimization passes may have killed... 242 Passes.add(createCFGSimplificationPass()); 243 244 // Now that we have optimized the program, discard unreachable functions... 245 Passes.add(createGlobalDCEPass()); 246 247 // Make sure everything is still good. 248 Passes.add(createVerifierPass()); 249 250 Target.addPassesToEmitFile(Passes, Out, TargetMachine::AssemblyFile, true); 251 252 // Run our queue of passes all at once now, efficiently. 253 Passes.run(*M); 254 255 return LTO_OPT_SUCCESS; 256} 257 258///Link all modules together and optimize them using IPO. Generate 259/// native object file using OutputFilename 260/// Return appropriate LTOStatus. 261enum LTOStatus 262LinkTimeOptimizer::optimizeModules(const std::string &OutputFilename, 263 std::vector<const char *> &exportList) 264{ 265 if (modules.empty()) 266 return LTO_NO_WORK; 267 268 std::ios::openmode io_mode = 269 std::ios::out | std::ios::trunc | std::ios::binary; 270 std::string *errMsg = NULL; 271 Module *bigOne = modules[0]; 272 Linker theLinker("LinkTimeOptimizer", bigOne, false); 273 for (unsigned i = 1, e = modules.size(); i != e; ++i) 274 if (theLinker.LinkModules(bigOne, modules[i], errMsg)) 275 return LTO_MODULE_MERGE_FAILURE; 276 277#if 0 278 // Enable this when -save-temps is used 279 std::ofstream Out("big.bc", io_mode); 280 WriteBytecodeToFile(bigOne, Out, true); 281#endif 282 283 // Strip leading underscore because it was added to match names 284 // seen by linker. 285 for (unsigned i = 0, e = exportList.size(); i != e; ++i) { 286 const char *name = exportList[i]; 287 if (strlen(name) > 2 && name[0] == '_') 288 exportList[i] = &name[1]; 289 } 290 291 sys::Path tmpAsmFilePath("/tmp/"); 292 tmpAsmFilePath.createTemporaryFileOnDisk(); 293 sys::RemoveFileOnSignal(tmpAsmFilePath); 294 295 std::ofstream asmFile(tmpAsmFilePath.c_str(), io_mode); 296 if (!asmFile.is_open() || asmFile.bad()) { 297 if (tmpAsmFilePath.exists()) 298 tmpAsmFilePath.eraseFromDisk(); 299 return LTO_WRITE_FAILURE; 300 } 301 302 enum LTOStatus status = lto_optimize(bigOne, asmFile, exportList); 303 asmFile.close(); 304 if (status != LTO_OPT_SUCCESS) { 305 tmpAsmFilePath.eraseFromDisk(); 306 return status; 307 } 308 309 // Run GCC to assemble and link the program into native code. 310 // 311 // Note: 312 // We can't just assemble and link the file with the system assembler 313 // and linker because we don't know where to put the _start symbol. 314 // GCC mysteriously knows how to do it. 315 const sys::Path gcc = FindExecutable("gcc", "/"); 316 if (gcc.isEmpty()) { 317 tmpAsmFilePath.eraseFromDisk(); 318 return LTO_ASM_FAILURE; 319 } 320 321 std::vector<const char*> args; 322 args.push_back(gcc.c_str()); 323 args.push_back("-c"); 324 args.push_back("-x"); 325 args.push_back("assembler"); 326 args.push_back("-o"); 327 args.push_back(OutputFilename.c_str()); 328 args.push_back(tmpAsmFilePath.c_str()); 329 args.push_back(0); 330 331 int R1 = sys::Program::ExecuteAndWait(gcc, &args[0], 0, 0, 1); 332 333 tmpAsmFilePath.eraseFromDisk(); 334 335 return LTO_OPT_SUCCESS; 336} 337