//===- FunctionImportUtils.h - Importing support utilities -----*- 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 FunctionImportGlobalProcessing class which is used
// to perform the necessary global value handling for function importing.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_UTILS_FUNCTIONIMPORTUTILS_H
#define LLVM_TRANSFORMS_UTILS_FUNCTIONIMPORTUTILS_H
#include "llvm/ADT/SetVector.h"
#include "llvm/IR/ModuleSummaryIndex.h"
namespace llvm {
class Module;
/// Class to handle necessary GlobalValue changes required by ThinLTO
/// function importing, including linkage changes and any necessary renaming.
class FunctionImportGlobalProcessing {
/// The Module which we are exporting or importing functions from.
Module &M;
/// Module summary index passed in for function importing/exporting handling.
const ModuleSummaryIndex &ImportIndex;
/// Globals to import from this module, all other functions will be
/// imported as declarations instead of definitions.
SetVector<GlobalValue *> *GlobalsToImport;
/// Set to true if the given ModuleSummaryIndex contains any functions
/// from this source module, in which case we must conservatively assume
/// that any of its functions may be imported into another module
/// as part of a different backend compilation process.
bool HasExportedFunctions = false;
/// Set to true (only applicatable to ELF -fpic) if dso_local should be
/// dropped for a declaration.
///
/// On ELF, the assembler is conservative and assumes a global default
/// visibility symbol can be interposable. No direct access relocation is
/// allowed, if the definition is not in the translation unit, even if the
/// definition is available in the linkage unit. Thus we need to clear
/// dso_local to disable direct access.
///
/// This flag should not be set for -fno-pic or -fpie, which would
/// unnecessarily disable direct access.
bool ClearDSOLocalOnDeclarations;
/// Set of llvm.*used values, in order to validate that we don't try
/// to promote any non-renamable values.
SmallPtrSet<GlobalValue *, 4> Used;
/// Keep track of any COMDATs that require renaming (because COMDAT
/// leader was promoted and renamed). Maps from original COMDAT to one
/// with new name.
DenseMap<const Comdat *, Comdat *> RenamedComdats;
/// Check if we should promote the given local value to global scope.
bool shouldPromoteLocalToGlobal(const GlobalValue *SGV, ValueInfo VI);
#ifndef NDEBUG
/// Check if the given value is a local that can't be renamed (promoted).
/// Only used in assertion checking, and disabled under NDEBUG since the Used
/// set will not be populated.
bool isNonRenamableLocal(const GlobalValue &GV) const;
#endif
/// Helper methods to check if we are importing from or potentially
/// exporting from the current source module.
bool isPerformingImport() const { return GlobalsToImport != nullptr; }
bool isModuleExporting() const { return HasExportedFunctions; }
/// If we are importing from the source module, checks if we should
/// import SGV as a definition, otherwise import as a declaration.
bool doImportAsDefinition(const GlobalValue *SGV);
/// Get the name for a local SGV that should be promoted and renamed to global
/// scope in the linked destination module.
std::string getPromotedName(const GlobalValue *SGV);
/// Process globals so that they can be used in ThinLTO. This includes
/// promoting local variables so that they can be reference externally by
/// thin lto imported globals and converting strong external globals to
/// available_externally.
void processGlobalsForThinLTO();
void processGlobalForThinLTO(GlobalValue &GV);
/// Get the new linkage for SGV that should be used in the linked destination
/// module. Specifically, for ThinLTO importing or exporting it may need
/// to be adjusted. When \p DoPromote is true then we must adjust the
/// linkage for a required promotion of a local to global scope.
GlobalValue::LinkageTypes getLinkage(const GlobalValue *SGV, bool DoPromote);
public:
FunctionImportGlobalProcessing(Module &M, const ModuleSummaryIndex &Index,
SetVector<GlobalValue *> *GlobalsToImport,
bool ClearDSOLocalOnDeclarations)
: M(M), ImportIndex(Index), GlobalsToImport(GlobalsToImport),
ClearDSOLocalOnDeclarations(ClearDSOLocalOnDeclarations) {
// If we have a ModuleSummaryIndex but no function to import,
// then this is the primary module being compiled in a ThinLTO
// backend compilation, and we need to see if it has functions that
// may be exported to another backend compilation.
if (!GlobalsToImport)
HasExportedFunctions = ImportIndex.hasExportedFunctions(M);
#ifndef NDEBUG
SmallVector<GlobalValue *, 4> Vec;
// First collect those in the llvm.used set.
collectUsedGlobalVariables(M, Vec, /*CompilerUsed=*/false);
// Next collect those in the llvm.compiler.used set.
collectUsedGlobalVariables(M, Vec, /*CompilerUsed=*/true);
Used = {Vec.begin(), Vec.end()};
#endif
}
bool run();
};
/// Perform in-place global value handling on the given Module for
/// exported local functions renamed and promoted for ThinLTO.
bool renameModuleForThinLTO(
Module &M, const ModuleSummaryIndex &Index,
bool ClearDSOLocalOnDeclarations,
SetVector<GlobalValue *> *GlobalsToImport = nullptr);
} // End llvm namespace
#endif