llvm/llvm/include/llvm/Transforms/IPO/FunctionImport.h

//===- llvm/Transforms/IPO/FunctionImport.h - ThinLTO importing -*- 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
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_TRANSFORMS_IPO_FUNCTIONIMPORT_H
#define LLVM_TRANSFORMS_IPO_FUNCTIONIMPORT_H

#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/ModuleSummaryIndex.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Support/Error.h"
#include <functional>
#include <map>
#include <memory>
#include <string>
#include <system_error>
#include <unordered_map>
#include <unordered_set>
#include <utility>

namespace llvm {

class Module;

/// The function importer is automatically importing function from other modules
/// based on the provided summary informations.
class FunctionImporter { … };

/// The function importing pass
class FunctionImportPass : public PassInfoMixin<FunctionImportPass> { … };

/// Compute all the imports and exports for every module in the Index.
///
/// \p ModuleToDefinedGVSummaries contains for each Module a map
/// (GUID -> Summary) for every global defined in the module.
///
/// \p isPrevailing is a callback that will be called with a global value's GUID
/// and summary and should return whether the module corresponding to the
/// summary contains the linker-prevailing copy of that value.
///
/// \p ImportLists will be populated with an entry for every Module we are
/// importing into. This entry is itself a map that can be passed to
/// FunctionImporter::importFunctions() above (see description there).
///
/// \p ExportLists contains for each Module the set of globals (GUID) that will
/// be imported by another module, or referenced by such a function. I.e. this
/// is the set of globals that need to be promoted/renamed appropriately.
///
/// The module identifier strings that are the keys of the above two maps
/// are owned by the in-memory ModuleSummaryIndex the importing decisions
/// are made from (the module path for each summary is owned by the index's
/// module path string table).
void ComputeCrossModuleImport(
    const ModuleSummaryIndex &Index,
    const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
    function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
        isPrevailing,
    FunctionImporter::ImportListsTy &ImportLists,
    DenseMap<StringRef, FunctionImporter::ExportSetTy> &ExportLists);

/// PrevailingType enum used as a return type of callback passed
/// to computeDeadSymbolsAndUpdateIndirectCalls. Yes and No values used when
/// status explicitly set by symbols resolution, otherwise status is Unknown.
enum class PrevailingType { … };

/// Update call edges for indirect calls to local functions added from
/// SamplePGO when needed. Normally this is done during
/// computeDeadSymbolsAndUpdateIndirectCalls, but can be called standalone
/// when that is not called (e.g. during testing).
void updateIndirectCalls(ModuleSummaryIndex &Index);

/// Compute all the symbols that are "dead": i.e these that can't be reached
/// in the graph from any of the given symbols listed in
/// \p GUIDPreservedSymbols. Non-prevailing symbols are symbols without a
/// prevailing copy anywhere in IR and are normally dead, \p isPrevailing
/// predicate returns status of symbol.
/// Also update call edges for indirect calls to local functions added from
/// SamplePGO when needed.
void computeDeadSymbolsAndUpdateIndirectCalls(
    ModuleSummaryIndex &Index,
    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
    function_ref<PrevailingType(GlobalValue::GUID)> isPrevailing);

/// Compute dead symbols and run constant propagation in combined index
/// after that.
void computeDeadSymbolsWithConstProp(
    ModuleSummaryIndex &Index,
    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
    function_ref<PrevailingType(GlobalValue::GUID)> isPrevailing,
    bool ImportEnabled);

/// Converts value \p GV to declaration, or replaces with a declaration if
/// it is an alias. Returns true if converted, false if replaced.
bool convertToDeclaration(GlobalValue &GV);

/// Compute the set of summaries needed for a ThinLTO backend compilation of
/// \p ModulePath.
//
/// This includes summaries from that module (in case any global summary based
/// optimizations were recorded) and from any definitions in other modules that
/// should be imported.
//
/// \p ModuleToSummariesForIndex will be populated with the needed summaries
/// from each required module path. Use a std::map instead of StringMap to get
/// stable order for bitcode emission.
///
/// \p DecSummaries will be popluated with the subset of of summary pointers
/// that have 'declaration' import type among all summaries the module need.
void gatherImportedSummariesForModule(
    StringRef ModulePath,
    const DenseMap<StringRef, GVSummaryMapTy> &ModuleToDefinedGVSummaries,
    const FunctionImporter::ImportMapTy &ImportList,
    ModuleToSummariesForIndexTy &ModuleToSummariesForIndex,
    GVSummaryPtrSet &DecSummaries);

/// Emit into \p OutputFilename the files module \p ModulePath will import from.
std::error_code
EmitImportsFiles(StringRef ModulePath, StringRef OutputFilename,
                 const ModuleToSummariesForIndexTy &ModuleToSummariesForIndex);

/// Based on the information recorded in the summaries during global
/// summary-based analysis:
/// 1. Resolve prevailing symbol linkages and constrain visibility (CanAutoHide
///    and consider visibility from other definitions for ELF) in \p TheModule
/// 2. (optional) Apply propagated function attributes to \p TheModule if
///    PropagateAttrs is true
void thinLTOFinalizeInModule(Module &TheModule,
                             const GVSummaryMapTy &DefinedGlobals,
                             bool PropagateAttrs);

/// Internalize \p TheModule based on the information recorded in the summaries
/// during global summary-based analysis.
void thinLTOInternalizeModule(Module &TheModule,
                              const GVSummaryMapTy &DefinedGlobals);

} // end namespace llvm

#endif // LLVM_TRANSFORMS_IPO_FUNCTIONIMPORT_H