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diff --git a/llvm/include/llvm/LTO/Config.h b/llvm/include/llvm/LTO/Config.h
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+//===-Config.h - LLVM Link Time Optimizer Configuration -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// 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/IR/DiagnosticInfo.h"
+#include "llvm/Support/CodeGen.h"
+#include "llvm/Target/TargetOptions.h"
+
+#include <functional>
+
+namespace llvm {
+
+class Error;
+class Module;
+class ModuleSummaryIndex;
+class raw_pwrite_stream;
+
+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 {
+  std::string CPU;
+  std::string Features;
+  TargetOptions Options;
+  std::vector<std::string> MAttrs;
+  Reloc::Model RelocModel = Reloc::PIC_;
+  CodeModel::Model CodeModel = CodeModel::Default;
+  CodeGenOpt::Level CGOptLevel = CodeGenOpt::Default;
+  unsigned OptLevel = 2;
+  bool DisableVerify = false;
+
+  /// 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;
+
+  bool ShouldDiscardValueNames = true;
+  DiagnosticHandlerFunction DiagHandler;
+
+  /// 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;
+
+  /// 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, or to add its own resolved symbols to the module. 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.
+  typedef std::function<bool(size_t Task, Module &)> ModuleHookFn;
+
+  /// 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.
+  typedef std::function<bool(const ModuleSummaryIndex &Index)>
+      CombinedIndexHookFn;
+  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.
+  Error addSaveTemps(std::string OutputFileName,
+                     bool UseInputModulePath = false);
+};
+
+/// This type defines a stream callback. A stream callback is used to add a
+/// native object that is generated on the fly. The callee must set up and
+/// return a output stream to write the native object to.
+///
+/// Stream callbacks must be thread safe.
+typedef std::function<std::unique_ptr<raw_pwrite_stream>(size_t Task)>
+    AddStreamFn;
+
+/// 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).
+struct LTOLLVMContext : LLVMContext {
+  static void funcDiagHandler(const DiagnosticInfo &DI, void *Context) {
+    auto *Fn = static_cast<DiagnosticHandlerFunction *>(Context);
+    (*Fn)(DI);
+  }
+
+  LTOLLVMContext(const Config &C) : DiagHandler(C.DiagHandler) {
+    setDiscardValueNames(C.ShouldDiscardValueNames);
+    enableDebugTypeODRUniquing();
+    setDiagnosticHandler(funcDiagHandler, &DiagHandler, true);
+  }
+  DiagnosticHandlerFunction DiagHandler;
+};
+
+}
+}
+
+#endif