lto.cpp revision a89d47f54d1f83d328f6169151653bfc742607bf
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 (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())); 96 } 97} 98 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. 103enum LTOStatus 104LinkTimeOptimizer::readLLVMObjectFile(const std::string &InputFilename, 105 NameToSymbolMap &symbols, 106 std::set<const char *> &references) 107{ 108 Module *m = ParseBytecodeFile(InputFilename); 109 if (!m) 110 return LTO_READ_FAILURE; 111 112 modules.push_back(m); 113 114 for (Module::iterator f = m->begin(), e = m->end(); f != e; ++f) { 115 116 LTOLinkageTypes lt = getLTOLinkageType(f); 117 118 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; 124 } 125 126 // 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(); 129 i != be; ++i) 130 for (unsigned count = 0, total = i->getNumOperands(); 131 count != total; ++count) 132 findExternalRefs(i->getOperand(count), references); 133 } 134 135 for (Module::global_iterator v = m->global_begin(), e = m->global_end(); 136 v != e; ++v) { 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; 143 } 144 } 145 146 return LTO_READ_SUCCESS; 147} 148 149/// 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. 153static enum LTOStatus lto_optimize(Module *M, std::ostream &Out, 154 std::vector<const char *> &exportList) 155{ 156 // Instantiate the pass manager to organize the passes. 157 PassManager Passes; 158 159 // Collect Target info 160 std::string Err; 161 const TargetMachineRegistry::Entry* March = 162 TargetMachineRegistry::getClosestStaticTargetForModule(*M, Err); 163 164 if (March == 0) 165 return LTO_NO_TARGET; 166 167 // Create target 168 std::string Features; 169 std::auto_ptr<TargetMachine> target(March->CtorFn(*M, Features)); 170 if (!target.get()) 171 return LTO_NO_TARGET; 172 173 TargetMachine &Target = *target.get(); 174 175 // Start off with a verification pass. 176 Passes.add(createVerifierPass()); 177 178 // Add an appropriate TargetData instance for this module... 179 Passes.add(new TargetData(*Target.getTargetData())); 180 181 // 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()); 186 187 // Internalize symbols if export list is nonemty 188 if (!exportList.empty()) 189 Passes.add(createInternalizePass(exportList)); 190 191 // Now that we internalized some globals, see if we can hack on them! 192 Passes.add(createGlobalOptimizerPass()); 193 194 // Linking modules together can lead to duplicated global constants, only 195 // keep one copy of each constant... 196 Passes.add(createConstantMergePass()); 197 198 // 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 200 // supporting. 201 Passes.add(createStripSymbolsPass()); 202 203 // Propagate constants at call sites into the functions they call. 204 Passes.add(createIPConstantPropagationPass()); 205 206 // Remove unused arguments from functions... 207 Passes.add(createDeadArgEliminationPass()); 208 209 Passes.add(createFunctionInliningPass()); // Inline small functions 210 211 Passes.add(createPruneEHPass()); // Remove dead EH info 212 213 Passes.add(createGlobalDCEPass()); // Remove dead functions 214 215 // 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()); 218 219 // The IPO passes may leave cruft around. Clean up after them. 220 Passes.add(createInstructionCombiningPass()); 221 222 Passes.add(createScalarReplAggregatesPass()); // Break up allocas 223 224 // Run a few AA driven optimizations here and now, to cleanup the code. 225 Passes.add(createGlobalsModRefPass()); // IP alias analysis 226 227 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 231 232 // Cleanup and simplify the code after the scalar optimizations. 233 Passes.add(createInstructionCombiningPass()); 234 235 // Delete basic blocks, which optimization passes may have killed... 236 Passes.add(createCFGSimplificationPass()); 237 238 // Now that we have optimized the program, discard unreachable functions... 239 Passes.add(createGlobalDCEPass()); 240 241 // Make sure everything is still good. 242 Passes.add(createVerifierPass()); 243 244 Target.addPassesToEmitFile(Passes, Out, TargetMachine::AssemblyFile, true); 245 246 // Run our queue of passes all at once now, efficiently. 247 Passes.run(*M); 248 249 return LTO_OPT_SUCCESS; 250} 251 252///Link all modules together and optimize them using IPO. Generate 253/// native object file using OutputFilename 254/// Return appropriate LTOStatus. 255enum LTOStatus 256LinkTimeOptimizer::optimizeModules(const std::string &OutputFilename, 257 std::vector<const char *> &exportList) 258{ 259 if (modules.empty()) 260 return LTO_NO_WORK; 261 262 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; 270 271#if 0 272 // Enable this when -save-temps is used 273 std::ofstream Out("big.bc", io_mode); 274 WriteBytecodeToFile(bigOne, Out, true); 275#endif 276 277 // Strip leading underscore because it was added to match names 278 // seen by liner. 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]; 283 } 284 285 sys::Path tmpAsmFilePath("/tmp/"); 286 tmpAsmFilePath.createTemporaryFileOnDisk(); 287 sys::RemoveFileOnSignal(tmpAsmFilePath); 288 289 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; 294 } 295 296 enum LTOStatus status = lto_optimize(bigOne, asmFile, exportList); 297 asmFile.close(); 298 if (status != LTO_OPT_SUCCESS) { 299 tmpAsmFilePath.eraseFromDisk(); 300 return status; 301 } 302 303 // Run GCC to assemble and link the program into native code. 304 // 305 // Note: 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", "/"); 310 if (gcc.isEmpty()) { 311 tmpAsmFilePath.eraseFromDisk(); 312 return LTO_ASM_FAILURE; 313 } 314 315 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()); 323 args.push_back(0); 324 325 int R1 = sys::Program::ExecuteAndWait(gcc, &args[0], 0, 0, 1); 326 327 tmpAsmFilePath.eraseFromDisk(); 328 329 return LTO_OPT_SUCCESS; 330} 331