Add new tool, lto, to do link time optimization. This tool installs
dynamic library that linker can use to optimize llvm byte codes at
link time.
llvm-svn: 29494
diff --git a/llvm/tools/lto/lto.cpp b/llvm/tools/lto/lto.cpp
new file mode 100644
index 0000000..3f3e8f9
--- /dev/null
+++ b/llvm/tools/lto/lto.cpp
@@ -0,0 +1,330 @@
+//===-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/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<const char *> &references) {
+
+ if (ConstantExpr *ce = dyn_cast<ConstantExpr>(value))
+ for (unsigned i = 0, e = ce->getNumOperands(); i != e; ++i)
+ findExternalRefs(ce->getOperand(i), references);
+ else if (GlobalValue *gv = dyn_cast<GlobalValue>(value)) {
+ LTOLinkageTypes lt = getLTOLinkageType(gv);
+ if (lt != LTOInternalLinkage && strncmp (gv->getName().c_str(), "llvm.", 5))
+ references.insert(addUnderscore(gv->getName().c_str()));
+ }
+}
+
+/// 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<const char *> &references)
+{
+ Module *m = ParseBytecodeFile(InputFilename);
+ if (!m)
+ return LTO_READ_FAILURE;
+
+ 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)) {
+ const char *name = addUnderscore(f->getName().c_str());
+ LLVMSymbol *newSymbol = new LLVMSymbol(lt, f);
+ symbols[name] = newSymbol;
+ allSymbols[name] = 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);
+ }
+
+ 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)) {
+ const char *name = addUnderscore(v->getName().c_str());
+ LLVMSymbol *newSymbol = new LLVMSymbol(lt,v);
+ symbols[name] = newSymbol;
+ }
+ }
+
+ 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 liner.
+ 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/");
+ tmpAsmFilePath.createTemporaryFileOnDisk();
+ 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);
+
+ int R1 = sys::Program::ExecuteAndWait(gcc, &args[0], 0, 0, 1);
+
+ tmpAsmFilePath.eraseFromDisk();
+
+ return LTO_OPT_SUCCESS;
+}