120 lines
4.8 KiB
C++
120 lines
4.8 KiB
C++
//===-LTO.cpp - LLVM Link Time Optimizer ----------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements functions and classes used to support LTO.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/LTO/LTO.h"
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#include "llvm/Bitcode/ReaderWriter.h"
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#include "llvm/Support/MemoryBuffer.h"
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#include "llvm/Support/SourceMgr.h"
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#include "llvm/Support/raw_ostream.h"
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namespace llvm {
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// Simple helper to load a module from bitcode
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std::unique_ptr<Module> loadModuleFromBuffer(const MemoryBufferRef &Buffer,
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LLVMContext &Context, bool Lazy) {
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SMDiagnostic Err;
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ErrorOr<std::unique_ptr<Module>> ModuleOrErr(nullptr);
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if (Lazy) {
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ModuleOrErr =
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getLazyBitcodeModule(MemoryBuffer::getMemBuffer(Buffer, false), Context,
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/* ShouldLazyLoadMetadata */ Lazy);
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} else {
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ModuleOrErr = parseBitcodeFile(Buffer, Context);
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}
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if (std::error_code EC = ModuleOrErr.getError()) {
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Err = SMDiagnostic(Buffer.getBufferIdentifier(), SourceMgr::DK_Error,
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EC.message());
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Err.print("ThinLTO", errs());
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report_fatal_error("Can't load module, abort.");
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}
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return std::move(ModuleOrErr.get());
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}
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static void thinLTOResolveWeakForLinkerGUID(
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GlobalValueSummaryList &GVSummaryList, GlobalValue::GUID GUID,
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DenseSet<GlobalValueSummary *> &GlobalInvolvedWithAlias,
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function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
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isPrevailing,
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function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
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recordNewLinkage) {
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for (auto &S : GVSummaryList) {
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if (GlobalInvolvedWithAlias.count(S.get()))
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continue;
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GlobalValue::LinkageTypes OriginalLinkage = S->linkage();
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if (!GlobalValue::isWeakForLinker(OriginalLinkage))
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continue;
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// We need to emit only one of these. The prevailing module will keep it,
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// but turned into a weak, while the others will drop it when possible.
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if (isPrevailing(GUID, S.get())) {
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if (GlobalValue::isLinkOnceLinkage(OriginalLinkage))
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S->setLinkage(GlobalValue::getWeakLinkage(
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GlobalValue::isLinkOnceODRLinkage(OriginalLinkage)));
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}
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// Alias can't be turned into available_externally.
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else if (!isa<AliasSummary>(S.get()) &&
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(GlobalValue::isLinkOnceODRLinkage(OriginalLinkage) ||
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GlobalValue::isWeakODRLinkage(OriginalLinkage)))
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S->setLinkage(GlobalValue::AvailableExternallyLinkage);
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if (S->linkage() != OriginalLinkage)
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recordNewLinkage(S->modulePath(), GUID, S->linkage());
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}
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}
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// Resolve Weak and LinkOnce values in the \p Index.
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//
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// We'd like to drop these functions if they are no longer referenced in the
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// current module. However there is a chance that another module is still
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// referencing them because of the import. We make sure we always emit at least
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// one copy.
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void thinLTOResolveWeakForLinkerInIndex(
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ModuleSummaryIndex &Index,
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function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
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isPrevailing,
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function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
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recordNewLinkage) {
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// We won't optimize the globals that are referenced by an alias for now
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// Ideally we should turn the alias into a global and duplicate the definition
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// when needed.
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DenseSet<GlobalValueSummary *> GlobalInvolvedWithAlias;
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for (auto &I : Index)
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for (auto &S : I.second)
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if (auto AS = dyn_cast<AliasSummary>(S.get()))
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GlobalInvolvedWithAlias.insert(&AS->getAliasee());
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for (auto &I : Index)
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thinLTOResolveWeakForLinkerGUID(I.second, I.first, GlobalInvolvedWithAlias,
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isPrevailing, recordNewLinkage);
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}
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static void thinLTOInternalizeAndPromoteGUID(
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GlobalValueSummaryList &GVSummaryList, GlobalValue::GUID GUID,
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function_ref<bool(StringRef, GlobalValue::GUID)> isExported) {
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for (auto &S : GVSummaryList) {
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if (isExported(S->modulePath(), GUID)) {
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if (GlobalValue::isLocalLinkage(S->linkage()))
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S->setLinkage(GlobalValue::ExternalLinkage);
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} else if (!GlobalValue::isLocalLinkage(S->linkage()))
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S->setLinkage(GlobalValue::InternalLinkage);
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}
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}
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// Update the linkages in the given \p Index to mark exported values
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// as external and non-exported values as internal.
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void thinLTOInternalizeAndPromoteInIndex(
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ModuleSummaryIndex &Index,
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function_ref<bool(StringRef, GlobalValue::GUID)> isExported) {
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for (auto &I : Index)
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thinLTOInternalizeAndPromoteGUID(I.second, I.first, isExported);
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}
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}
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