Config.h

Go to the documentation of this file.

//===-Config.h - LLVM Link Time Optimizer Configuration ---------*- C++ -*-===//
//
// 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 defines the lto::Config data structure, which allows clients to
// configure LTO.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_LTO_CONFIG_H
#define LLVM_LTO_CONFIG_H
 
#include "llvm/ADT/DenseSet.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/Passes/PassBuilder.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/LibraryOptionsContext.h"
#include "llvm/Target/TargetOptions.h"
 
#include <functional>
#include <optional>
 
namespace llvm {
 
class Error;
class Module;
class ModuleSummaryIndex;
class raw_pwrite_stream;
class PassPlugin;
 
namespace lto {
 
/// LTO configuration. A linker can configure LTO by setting fields in this data
/// structure and passing it to the lto::LTO constructor.
struct Config {
  enum VisScheme {
    FromPrevailing,
    ELF,
  };
  // The library options of every LLVMContext that LTO creates.
  // TODO: Make it non-null once every client sets it. Null means the defaults.
  const cl::LibraryOptionsContext *LibraryOptions = nullptr;
  // Note: when adding fields here, consider whether they need to be added to
  // computeLTOCacheKey in LTO.cpp.
  std::string CPU;
  TargetOptions Options;
  std::vector<std::string> MAttrs;
  std::vector<std::string> MllvmArgs;
  // LTO will register both lists of plugins, but
  // if an LTO client has already loaded a set of plugins,
  // they should register them via LoadedPassPlugins.
  // LoadedPassPlugins is currently used by distributed thin-lto.
  std::vector<llvm::PassPlugin *> LoadedPassPlugins;
  std::vector<std::string> PassPluginFilenames;
  /// For adding passes that run right before codegen.
  std::function<void(legacy::PassManager &)> PreCodeGenPassesHook;
  std::function<void(PassBuilder &)> PassBuilderCallback;
  std::optional<Reloc::Model> RelocModel = Reloc::PIC_;
  std::optional<CodeModel::Model> CodeModel;
  CodeGenOptLevel CGOptLevel = CodeGenOptLevel::Default;
  CodeGenFileType CGFileType = CodeGenFileType::ObjectFile;
  unsigned OptLevel = 2;
  bool VerifyEach = false;
  bool DisableVerify = false;
 
  /// Flag to indicate that the optimizer should not assume builtins are present
  /// on the target.
  bool Freestanding = false;
 
  /// Disable entirely the optimizer, including importing for ThinLTO
  bool CodeGenOnly = false;
 
  /// Run PGO context sensitive IR instrumentation.
  bool RunCSIRInstr = false;
 
  /// Turn on/off the warning about a hash mismatch in the PGO profile data.
  bool PGOWarnMismatch = true;
 
  /// Asserts whether we can assume whole program visibility during the LTO
  /// link.
  bool HasWholeProgramVisibility = false;
 
  /// We're validating that all native vtables have corresponding type infos.
  bool ValidateAllVtablesHaveTypeInfos = false;
  /// If all native vtables have corresponding type infos, allow
  /// usage of RTTI to block devirtualization on types used in native files.
  bool AllVtablesHaveTypeInfos = false;
 
  /// Always emit a Regular LTO object even when it is empty because no Regular
  /// LTO modules were linked. This option is useful for some build system which
  /// want to know a priori all possible output files.
  bool AlwaysEmitRegularLTOObj = false;
 
  /// If true, the LTO instance creates copies of the symbol names for LTO::run.
  /// The lld linker uses string saver to keep symbol names alive and doesn't
  /// need to create copies, so it can set this field to false.
  bool KeepSymbolNameCopies = true;
 
  /// This flag is used as one of parameters to calculate cache entries and to
  /// ensure that in-process cache and out-of-process (DTLTO) cache are
  /// distinguished.
  mutable bool Dtlto = 0;
 
  /// Allows non-imported definitions to get the potentially more constraining
  /// visibility from the prevailing definition. FromPrevailing is the default
  /// because it works for many binary formats. ELF can use the more optimized
  /// 'ELF' scheme.
  VisScheme VisibilityScheme = FromPrevailing;
 
  /// If this field is set, the set of passes run in the middle-end optimizer
  /// will be the one specified by the string. Only works with the new pass
  /// manager as the old one doesn't have this ability.
  std::string OptPipeline;
 
  // If this field is set, it has the same effect of specifying an AA pipeline
  // identified by the string. Only works with the new pass manager, in
  // conjunction OptPipeline.
  std::string AAPipeline;
 
  /// Setting this field will replace target triples in input files with this
  /// triple.
  std::string OverrideTriple;
 
  /// Setting this field will replace unspecified target triples in input files
  /// with this triple.
  std::string DefaultTriple;
 
  /// Context Sensitive PGO profile path.
  std::string CSIRProfile;
 
  /// Sample PGO profile path.
  std::string SampleProfile;
 
  /// Name remapping file for profile data.
  std::string ProfileRemapping;
 
  /// The directory to store .dwo files.
  std::string DwoDir;
 
  /// The name for the split debug info file used for the DW_AT_[GNU_]dwo_name
  /// attribute in the skeleton CU. This should generally only be used when
  /// running an individual backend directly via thinBackend(), as otherwise
  /// all objects would use the same .dwo file. Not used as output path.
  std::string SplitDwarfFile;
 
  /// The path to write a .dwo file to. This should generally only be used when
  /// running an individual backend directly via thinBackend(), as otherwise
  /// all .dwo files will be written to the same path. Not used in skeleton CU.
  std::string SplitDwarfOutput;
 
  /// Optimization remarks file path.
  std::string RemarksFilename;
 
  /// Optimization remarks pass filter.
  std::string RemarksPasses;
 
  /// Whether to emit optimization remarks with hotness informations.
  bool RemarksWithHotness = false;
 
  /// The minimum hotness value a diagnostic needs in order to be included in
  /// optimization diagnostics.
  ///
  /// The threshold is an Optional value, which maps to one of the 3 states:
  /// 1. 0            => threshold disabled. All emarks will be printed.
  /// 2. positive int => manual threshold by user. Remarks with hotness exceed
  ///                    threshold will be printed.
  /// 3. None         => 'auto' threshold by user. The actual value is not
  ///                    available at command line, but will be synced with
  ///                    hotness threhold from profile summary during
  ///                    compilation.
  ///
  /// If threshold option is not specified, it is disabled by default.
  std::optional<uint64_t> RemarksHotnessThreshold = 0;
 
  /// The format used for serializing remarks (default: YAML).
  std::string RemarksFormat;
 
  /// Whether to emit the pass manager debuggging informations.
  bool DebugPassManager = false;
 
  /// Statistics output file path.
  std::string StatsFile;
 
  /// Specific thinLTO modules to compile.
  std::vector<std::string> ThinLTOModulesToCompile;
 
  /// Time trace enabled.
  bool TimeTraceEnabled = false;
 
  /// Time trace granularity.
  unsigned TimeTraceGranularity = 500;
 
  bool ShouldDiscardValueNames = true;
  DiagnosticHandlerFunction DiagHandler;
 
  /// Add FSAFDO discriminators.
  bool AddFSDiscriminator = false;
 
  /// If this field is set, LTO will write input file paths and symbol
  /// resolutions here in llvm-lto2 command line flag format. This can be
  /// used for testing and for running the LTO pipeline outside of the linker
  /// with llvm-lto2.
  std::unique_ptr<raw_ostream> ResolutionFile;
 
  /// Tunable parameters for passes in the default pipelines.
  PipelineTuningOptions PTO;
 
  /// The following callbacks deal with tasks, which normally represent the
  /// entire optimization and code generation pipeline for what will become a
  /// single native object file. Each task has a unique identifier between 0 and
  /// getMaxTasks()-1, which is supplied to the callback via the Task parameter.
  /// A task represents the entire pipeline for ThinLTO and regular
  /// (non-parallel) LTO, but a parallel code generation task will be split into
  /// N tasks before code generation, where N is the parallelism level.
  ///
  /// LTO may decide to stop processing a task at any time, for example if the
  /// module is empty or if a module hook (see below) returns false. For this
  /// reason, the client should not expect to receive exactly getMaxTasks()
  /// native object files.
 
  /// A module hook may be used by a linker to perform actions during the LTO
  /// pipeline. For example, a linker may use this function to implement
  /// -save-temps. If this function returns false, any further processing for
  /// that task is aborted.
  ///
  /// Module hooks must be thread safe with respect to the linker's internal
  /// data structures. A module hook will never be called concurrently from
  /// multiple threads with the same task ID, or the same module.
  ///
  /// Note that in out-of-process backend scenarios, none of the hooks will be
  /// called for ThinLTO tasks.
  using ModuleHookFn = std::function<bool(unsigned Task, const Module &)>;
 
  /// This module hook is called after linking (regular LTO) or loading
  /// (ThinLTO) the module, before modifying it.
  ModuleHookFn PreOptModuleHook;
 
  /// This hook is called after promoting any internal functions
  /// (ThinLTO-specific).
  ModuleHookFn PostPromoteModuleHook;
 
  /// This hook is called after internalizing the module.
  ModuleHookFn PostInternalizeModuleHook;
 
  /// This hook is called after importing from other modules (ThinLTO-specific).
  ModuleHookFn PostImportModuleHook;
 
  /// This module hook is called after optimization is complete.
  ModuleHookFn PostOptModuleHook;
 
  /// This module hook is called before code generation. It is similar to the
  /// PostOptModuleHook, but for parallel code generation it is called after
  /// splitting the module.
  ModuleHookFn PreCodeGenModuleHook;
 
  /// A combined index hook is called after all per-module indexes have been
  /// combined (ThinLTO-specific). It can be used to implement -save-temps for
  /// the combined index.
  ///
  /// If this function returns false, any further processing for ThinLTO tasks
  /// is aborted.
  ///
  /// It is called regardless of whether the backend is in-process, although it
  /// is not called from individual backend processes.
  using CombinedIndexHookFn = std::function<bool(
      const ModuleSummaryIndex &Index,
      const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols)>;
  CombinedIndexHookFn CombinedIndexHook;
 
  /// This is a convenience function that configures this Config object to write
  /// temporary files named after the given OutputFileName for each of the LTO
  /// phases to disk. A client can use this function to implement -save-temps.
  ///
  /// FIXME: Temporary files derived from ThinLTO backends are currently named
  /// after the input file name, rather than the output file name, when
  /// UseInputModulePath is set to true.
  ///
  /// Specifically, it (1) sets each of the above module hooks and the combined
  /// index hook to a function that calls the hook function (if any) that was
  /// present in the appropriate field when the addSaveTemps function was
  /// called, and writes the module to a bitcode file with a name prefixed by
  /// the given output file name, and (2) creates a resolution file whose name
  /// is prefixed by the given output file name and sets ResolutionFile to its
  /// file handle.
  ///
  /// SaveTempsArgs can be specified to select which temps to save.
  /// If SaveTempsArgs is not provided, all temps are saved.
  LLVM_ABI Error addSaveTemps(std::string OutputFileName,
                              bool UseInputModulePath = false,
                              const DenseSet<StringRef> &SaveTempsArgs = {});
 
  /// Called by WriteIndexesThinBackend when it needs to write a bitcode
  /// module's summary index. The callback should return a stream to write
  /// the index into. If not set, the backend falls back
  /// to writing the summary index to a file.
  std::function<std::unique_ptr<raw_pwrite_stream>(size_t Task)>
      GetSummaryIndexOutputStream;
  /// Called by WriteIndexesThinBackend when it needs to store a bitcode
  /// module's imports list. The callback should return a vector that the
  /// backend will populate with the imported module paths. If not set, the
  /// backend writes the imports list to a file instead.
  std::function<std::vector<std::string> &(size_t Task)>
      GetImportsListOutputArray;
  /// Called by WriteIndexesThinBackend when it needs to store a bitcode
  /// module's cache key. The callback should return a string that the backend
  /// will fill with the computed cache key. If not set, the cache key is
  /// discarded.
  std::function<std::string &(size_t Task)> GetCacheKeyOutputString;
};
 
struct LTOLLVMDiagnosticHandler : public DiagnosticHandler {
  DiagnosticHandlerFunction *Fn;
  LTOLLVMDiagnosticHandler(DiagnosticHandlerFunction *DiagHandlerFn)
      : Fn(DiagHandlerFn) {}
  bool handleDiagnostics(const DiagnosticInfo &DI) override {
    (*Fn)(DI);
    return true;
  }
};
/// A derived class of LLVMContext that initializes itself according to a given
/// Config object. The purpose of this class is to tie ownership of the
/// diagnostic handler to the context, as opposed to the Config object (which
/// may be ephemeral).
// FIXME: This should not be required as diagnostic handler is not callback.
struct LTOLLVMContext : LLVMContext {
 
  LTOLLVMContext(const Config &C) : DiagHandler(C.DiagHandler) {
    setDiscardValueNames(C.ShouldDiscardValueNames);
    enableDebugTypeODRUniquing();
    setDiagnosticHandler(
        std::make_unique<LTOLLVMDiagnosticHandler>(&DiagHandler), true);
    if (C.LibraryOptions)
      getLibraryOptions().assign(*C.LibraryOptions);
  }
  DiagnosticHandlerFunction DiagHandler;
};
 
}
}
 
#endif