LTO.h | Explore in Territory

//===-LTO.h - LLVM Link Time Optimizer ------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file declares functions and classes used to support LTO. It is intended
// to be used both by LTO classes as well as by clients (gold-plugin) that
// don't utilize the LTO code generator interfaces.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LTO_LTO_H
#define LLVM_LTO_LTO_H

#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Bitcode/BitcodeReader.h"
#include "llvm/IR/ModuleSummaryIndex.h"
#include "llvm/LTO/Config.h"
#include "llvm/Object/IRSymtab.h"
#include "llvm/Support/Caching.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/thread.h"
#include "llvm/Transforms/IPO/FunctionAttrs.h"
#include "llvm/Transforms/IPO/FunctionImport.h"

namespace llvm {

class Error;
class IRMover;
class LLVMContext;
class MemoryBufferRef;
class Module;
class raw_pwrite_stream;
class ToolOutputFile;

/// Resolve linkage for prevailing symbols in the \p Index. Linkage changes
/// recorded in the index and the ThinLTO backends must apply the changes to
/// the module via thinLTOFinalizeInModule.
///
/// This is done for correctness (if value exported, ensure we always
/// emit a copy), and compile-time optimization (allow drop of duplicates).
void thinLTOResolvePrevailingInIndex(
    const lto::Config &C, ModuleSummaryIndex &Index,
    function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
        isPrevailing,
    function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
        recordNewLinkage,
    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols);

/// Update the linkages in the given \p Index to mark exported values
/// as external and non-exported values as internal. The ThinLTO backends
/// must apply the changes to the Module via thinLTOInternalizeModule.
void thinLTOInternalizeAndPromoteInIndex(
    ModuleSummaryIndex &Index,
    function_ref<bool(StringRef, ValueInfo)> isExported,
    function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
        isPrevailing);

/// Computes a unique hash for the Module considering the current list of
/// export/import and other global analysis results.
std::string computeLTOCacheKey(
    const lto::Config &Conf, const ModuleSummaryIndex &Index,
    StringRef ModuleID, const FunctionImporter::ImportMapTy &ImportList,
    const FunctionImporter::ExportSetTy &ExportList,
    const std::map<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR,
    const GVSummaryMapTy &DefinedGlobals,
    const DenseSet<GlobalValue::GUID> &CfiFunctionDefs = { … };

namespace lto {

StringLiteral getThinLTODefaultCPU(const Triple &TheTriple);

/// Given the original \p Path to an output file, replace any path
/// prefix matching \p OldPrefix with \p NewPrefix. Also, create the
/// resulting directory if it does not yet exist.
std::string getThinLTOOutputFile(StringRef Path, StringRef OldPrefix,
                                 StringRef NewPrefix);

/// Setup optimization remarks.
Expected<std::unique_ptr<ToolOutputFile>> setupLLVMOptimizationRemarks(
    LLVMContext &Context, StringRef RemarksFilename, StringRef RemarksPasses,
    StringRef RemarksFormat, bool RemarksWithHotness,
    std::optional<uint64_t> RemarksHotnessThreshold = 0, int Count = -1);

/// Setups the output file for saving statistics.
Expected<std::unique_ptr<ToolOutputFile>>
setupStatsFile(StringRef StatsFilename);

/// Produces a container ordering for optimal multi-threaded processing. Returns
/// ordered indices to elements in the input array.
std::vector<int> generateModulesOrdering(ArrayRef<BitcodeModule *> R);

/// Updates MemProf attributes (and metadata) based on whether the index
/// has recorded that we are linking with allocation libraries containing
/// the necessary APIs for downstream transformations.
void updateMemProfAttributes(Module &Mod, const ModuleSummaryIndex &Index);

class LTO;
struct SymbolResolution;
class ThinBackendProc;

/// An input file. This is a symbol table wrapper that only exposes the
/// information that an LTO client should need in order to do symbol resolution.
class InputFile { … };

/// A ThinBackend defines what happens after the thin-link phase during ThinLTO.
/// The details of this type definition aren't important; clients can only
/// create a ThinBackend using one of the create*ThinBackend() functions below.
ThinBackend;

/// This ThinBackend runs the individual backend jobs in-process.
/// The default value means to use one job per hardware core (not hyper-thread).
/// OnWrite is callback which receives module identifier and notifies LTO user
/// that index file for the module (and optionally imports file) was created.
/// ShouldEmitIndexFiles being true will write sharded ThinLTO index files
/// to the same path as the input module, with suffix ".thinlto.bc"
/// ShouldEmitImportsFiles is true it also writes a list of imported files to a
/// similar path with ".imports" appended instead.
IndexWriteCallback;
ThinBackend createInProcessThinBackend(ThreadPoolStrategy Parallelism,
                                       IndexWriteCallback OnWrite = nullptr,
                                       bool ShouldEmitIndexFiles = false,
                                       bool ShouldEmitImportsFiles = false);

/// This ThinBackend writes individual module indexes to files, instead of
/// running the individual backend jobs. This backend is for distributed builds
/// where separate processes will invoke the real backends.
///
/// To find the path to write the index to, the backend checks if the path has a
/// prefix of OldPrefix; if so, it replaces that prefix with NewPrefix. It then
/// appends ".thinlto.bc" and writes the index to that path. If
/// ShouldEmitImportsFiles is true it also writes a list of imported files to a
/// similar path with ".imports" appended instead.
/// LinkedObjectsFile is an output stream to write the list of object files for
/// the final ThinLTO linking. Can be nullptr.  If LinkedObjectsFile is not
/// nullptr and NativeObjectPrefix is not empty then it replaces the prefix of
/// the objects with NativeObjectPrefix instead of NewPrefix. OnWrite is
/// callback which receives module identifier and notifies LTO user that index
/// file for the module (and optionally imports file) was created.
ThinBackend createWriteIndexesThinBackend(std::string OldPrefix,
                                          std::string NewPrefix,
                                          std::string NativeObjectPrefix,
                                          bool ShouldEmitImportsFiles,
                                          raw_fd_ostream *LinkedObjectsFile,
                                          IndexWriteCallback OnWrite);

/// This class implements a resolution-based interface to LLVM's LTO
/// functionality. It supports regular LTO, parallel LTO code generation and
/// ThinLTO. You can use it from a linker in the following way:
/// - Set hooks and code generation options (see lto::Config struct defined in
///   Config.h), and use the lto::Config object to create an lto::LTO object.
/// - Create lto::InputFile objects using lto::InputFile::create(), then use
///   the symbols() function to enumerate its symbols and compute a resolution
///   for each symbol (see SymbolResolution below).
/// - After the linker has visited each input file (and each regular object
///   file) and computed a resolution for each symbol, take each lto::InputFile
///   and pass it and an array of symbol resolutions to the add() function.
/// - Call the getMaxTasks() function to get an upper bound on the number of
///   native object files that LTO may add to the link.
/// - Call the run() function. This function will use the supplied AddStream
///   and Cache functions to add up to getMaxTasks() native object files to
///   the link.
class LTO { … };

/// The resolution for a symbol. The linker must provide a SymbolResolution for
/// each global symbol based on its internal resolution of that symbol.
struct SymbolResolution { … };

} // namespace lto
} // namespace llvm

#endif
llvm/llvm/include/llvm/LTO/LTO.h
