tools/lto/lto.cpp

//===-lto.cpp - LLVM Link Time Optimizer ----------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Devang Patel and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implementes link time optimization library. This library is
// intended to be used by linker to optimize code at link time.
//
//===----------------------------------------------------------------------===//

#include "llvm/Module.h"
#include "llvm/PassManager.h"
#include "llvm/Linker.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/SymbolTable.h"
#include "llvm/Bytecode/Reader.h"
#include "llvm/Bytecode/Writer.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/FileUtilities.h"
#include "llvm/Support/SystemUtils.h"
#include "llvm/Support/Mangler.h"
#include "llvm/System/Program.h"
#include "llvm/System/Signals.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/Verifier.h"
#include "llvm/Target/SubtargetFeature.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetMachineRegistry.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Analysis/LoadValueNumbering.h"
#include "llvm/LinkTimeOptimizer.h"
#include <fstream>
#include <iostream>

using namespace llvm;

extern "C"
llvm::LinkTimeOptimizer *createLLVMOptimizer()
{
  llvm::LinkTimeOptimizer *l = new llvm::LinkTimeOptimizer();
  return l;
}


/// If symbol is not used then make it internal and let optimizer takes
/// care of it.
void LLVMSymbol::mayBeNotUsed() {
  gv->setLinkage(GlobalValue::InternalLinkage);
}

// Helper routine
// FIXME : Take advantage of GlobalPrefix from AsmPrinter
static const char *addUnderscore(const char *name) {
  size_t namelen = strlen(name);
  char *symName = (char*)malloc(namelen+2);
  symName[0] = '_';
  strcpy(&symName[1], name);
  return symName;
}

// Map LLVM LinkageType to LTO LinakgeType
static LTOLinkageTypes
getLTOLinkageType(GlobalValue *v)
{
  LTOLinkageTypes lt;
  if (v->hasExternalLinkage())
    lt = LTOExternalLinkage;
  else if (v->hasLinkOnceLinkage())
    lt = LTOLinkOnceLinkage;
  else if (v->hasWeakLinkage())
    lt = LTOWeakLinkage;
  else
    // Otherwise it is internal linkage for link time optimizer
    lt = LTOInternalLinkage;
  return lt;
}

// Find exeternal symbols referenced by VALUE. This is a recursive function.
static void
findExternalRefs(Value *value, std::set<std::string> &references,
                 Mangler &mangler) {

  if (GlobalValue *gv = dyn_cast<GlobalValue>(value)) {
    LTOLinkageTypes lt = getLTOLinkageType(gv);
    if (lt != LTOInternalLinkage && strncmp (gv->getName().c_str(), "llvm.", 5))
      references.insert(mangler.getValueName(gv));
  }
  else if (Constant *c = dyn_cast<Constant>(value))
    // Handle ConstantExpr, ConstantStruct, ConstantArry etc..
    for (unsigned i = 0, e = c->getNumOperands(); i != e; ++i)
      findExternalRefs(c->getOperand(i), references, mangler);
}

/// InputFilename is a LLVM bytecode file. Read it using bytecode reader.
/// Collect global functions and symbol names in symbols vector.
/// Collect external references in references vector.
/// Return LTO_READ_SUCCESS if there is no error.
enum LTOStatus
LinkTimeOptimizer::readLLVMObjectFile(const std::string &InputFilename,
                                      NameToSymbolMap &symbols,
                                      std::set<std::string> &references)
{
  Module *m = ParseBytecodeFile(InputFilename);
  if (!m)
    return LTO_READ_FAILURE;

  // Use mangler to add GlobalPrefix to names to match linker names.
  // FIXME : Instead of hard coding "-" use GlobalPrefix.
  Mangler mangler(*m, "_");

  modules.push_back(m);

  for (Module::iterator f = m->begin(), e = m->end(); f != e; ++f) {

    LTOLinkageTypes lt = getLTOLinkageType(f);

    if (!f->isExternal() && lt != LTOInternalLinkage
        && strncmp (f->getName().c_str(), "llvm.", 5)) {
      LLVMSymbol *newSymbol = new LLVMSymbol(lt, f, f->getName(),
                                             mangler.getValueName(f));
      symbols[newSymbol->getMangledName()] = newSymbol;
      allSymbols[newSymbol->getMangledName()] = newSymbol;
    }

    // Collect external symbols referenced by this function.
    for (Function::iterator b = f->begin(), fe = f->end(); b != fe; ++b)
      for (BasicBlock::iterator i = b->begin(), be = b->end();
           i != be; ++i)
        for (unsigned count = 0, total = i->getNumOperands();
             count != total; ++count)
          findExternalRefs(i->getOperand(count), references, mangler);
  }

  for (Module::global_iterator v = m->global_begin(), e = m->global_end();
       v !=  e; ++v) {
    LTOLinkageTypes lt = getLTOLinkageType(v);
    if (!v->isExternal() && lt != LTOInternalLinkage
        && strncmp (v->getName().c_str(), "llvm.", 5)) {
      LLVMSymbol *newSymbol = new LLVMSymbol(lt, v, v->getName(),
                                             mangler.getValueName(v));
      symbols[newSymbol->getMangledName()] = newSymbol;

      for (unsigned count = 0, total = v->getNumOperands();
           count != total; ++count)
        findExternalRefs(v->getOperand(count), references, mangler);

    }
  }

  return LTO_READ_SUCCESS;
}

/// Optimize module M using various IPO passes. Use exportList to
/// internalize selected symbols. Target platform is selected
/// based on information available to module M. No new target
/// features are selected.
static enum LTOStatus lto_optimize(Module *M, std::ostream &Out,
                                   std::vector<const char *> &exportList)
{
  // Instantiate the pass manager to organize the passes.
  PassManager Passes;

  // Collect Target info
  std::string Err;
  const TargetMachineRegistry::Entry* March =
    TargetMachineRegistry::getClosestStaticTargetForModule(*M, Err);

  if (March == 0)
    return LTO_NO_TARGET;

  // Create target
  std::string Features;
  std::auto_ptr<TargetMachine> target(March->CtorFn(*M, Features));
  if (!target.get())
    return LTO_NO_TARGET;

  TargetMachine &Target = *target.get();

  // Start off with a verification pass.
  Passes.add(createVerifierPass());

  // Add an appropriate TargetData instance for this module...
  Passes.add(new TargetData(*Target.getTargetData()));

  // Often if the programmer does not specify proper prototypes for the
  // functions they are calling, they end up calling a vararg version of the
  // function that does not get a body filled in (the real function has typed
  // arguments).  This pass merges the two functions.
  Passes.add(createFunctionResolvingPass());

  // Internalize symbols if export list is nonemty
  if (!exportList.empty())
    Passes.add(createInternalizePass(exportList));

  // Now that we internalized some globals, see if we can hack on them!
  Passes.add(createGlobalOptimizerPass());

  // Linking modules together can lead to duplicated global constants, only
  // keep one copy of each constant...
  Passes.add(createConstantMergePass());

  // If the -s command line option was specified, strip the symbols out of the
  // resulting program to make it smaller.  -s is a GLD option that we are
  // supporting.
  Passes.add(createStripSymbolsPass());

  // Propagate constants at call sites into the functions they call.
  Passes.add(createIPConstantPropagationPass());

  // Remove unused arguments from functions...
  Passes.add(createDeadArgEliminationPass());

  Passes.add(createFunctionInliningPass()); // Inline small functions

  Passes.add(createPruneEHPass());            // Remove dead EH info

  Passes.add(createGlobalDCEPass());          // Remove dead functions

  // If we didn't decide to inline a function, check to see if we can
  // transform it to pass arguments by value instead of by reference.
  Passes.add(createArgumentPromotionPass());

  // The IPO passes may leave cruft around.  Clean up after them.
  Passes.add(createInstructionCombiningPass());

  Passes.add(createScalarReplAggregatesPass()); // Break up allocas

  // Run a few AA driven optimizations here and now, to cleanup the code.
  Passes.add(createGlobalsModRefPass());      // IP alias analysis

  Passes.add(createLICMPass());               // Hoist loop invariants
  Passes.add(createLoadValueNumberingPass()); // GVN for load instrs
  Passes.add(createGCSEPass());               // Remove common subexprs
  Passes.add(createDeadStoreEliminationPass()); // Nuke dead stores

  // Cleanup and simplify the code after the scalar optimizations.
  Passes.add(createInstructionCombiningPass());

  // Delete basic blocks, which optimization passes may have killed...
  Passes.add(createCFGSimplificationPass());

  // Now that we have optimized the program, discard unreachable functions...
  Passes.add(createGlobalDCEPass());

  // Make sure everything is still good.
  Passes.add(createVerifierPass());

  Target.addPassesToEmitFile(Passes, Out, TargetMachine::AssemblyFile, true);

  // Run our queue of passes all at once now, efficiently.
  Passes.run(*M);

  return LTO_OPT_SUCCESS;
}

///Link all modules together and optimize them using IPO. Generate
/// native object file using OutputFilename
/// Return appropriate LTOStatus.
enum LTOStatus
LinkTimeOptimizer::optimizeModules(const std::string &OutputFilename,
                                   std::vector<const char *> &exportList)
{
  if (modules.empty())
    return LTO_NO_WORK;

  std::ios::openmode io_mode =
    std::ios::out | std::ios::trunc | std::ios::binary;
  std::string *errMsg = NULL;
  Module *bigOne = modules[0];
  Linker theLinker("LinkTimeOptimizer", bigOne, false);
  for (unsigned i = 1, e = modules.size(); i != e; ++i)
    if (theLinker.LinkModules(bigOne, modules[i], errMsg))
      return LTO_MODULE_MERGE_FAILURE;

#if 0
  // Enable this when -save-temps is used
  std::ofstream Out("big.bc", io_mode);
  WriteBytecodeToFile(bigOne, Out, true);
#endif

  // Strip leading underscore because it was added to match names
  // seen by linker.
  for (unsigned i = 0, e = exportList.size(); i != e; ++i) {
    const char *name = exportList[i];
    if (strlen(name) > 2 && name[0] == '_')
      exportList[i] = &name[1];
  }

  sys::Path tmpAsmFilePath("/tmp/");
  std::string ErrMsg;
  if (tmpAsmFilePath.createTemporaryFileOnDisk(&ErrMsg)) {
    std::cerr << "lto: " << ErrMsg << "\n";
    return LTO_WRITE_FAILURE;
  }
  sys::RemoveFileOnSignal(tmpAsmFilePath);

  std::ofstream asmFile(tmpAsmFilePath.c_str(), io_mode);
  if (!asmFile.is_open() || asmFile.bad()) {
    if (tmpAsmFilePath.exists())
      tmpAsmFilePath.eraseFromDisk();
    return LTO_WRITE_FAILURE;
  }

  enum LTOStatus status = lto_optimize(bigOne, asmFile, exportList);
  asmFile.close();
  if (status != LTO_OPT_SUCCESS) {
    tmpAsmFilePath.eraseFromDisk();
    return status;
  }

  // Run GCC to assemble and link the program into native code.
  //
  // Note:
  //  We can't just assemble and link the file with the system assembler
  //  and linker because we don't know where to put the _start symbol.
  //  GCC mysteriously knows how to do it.
  const sys::Path gcc = FindExecutable("gcc", "/");
  if (gcc.isEmpty()) {
    tmpAsmFilePath.eraseFromDisk();
    return LTO_ASM_FAILURE;
  }

  std::vector<const char*> args;
  args.push_back(gcc.c_str());
  args.push_back("-c");
  args.push_back("-x");
  args.push_back("assembler");
  args.push_back("-o");
  args.push_back(OutputFilename.c_str());
  args.push_back(tmpAsmFilePath.c_str());
  args.push_back(0);

  sys::Program::ExecuteAndWait(gcc, &args[0], 0, 0, 1);

  tmpAsmFilePath.eraseFromDisk();

  return LTO_OPT_SUCCESS;
}