1//===-LTO.cpp - LLVM Link Time Optimizer ----------------------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements functions and classes used to support LTO.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/LTO/LTO.h"
15#include "llvm/Bitcode/ReaderWriter.h"
16#include "llvm/Support/MemoryBuffer.h"
17#include "llvm/Support/SourceMgr.h"
18#include "llvm/Support/raw_ostream.h"
19
20namespace llvm {
21
22// Simple helper to load a module from bitcode
23std::unique_ptr<Module> loadModuleFromBuffer(const MemoryBufferRef &Buffer,
24                                             LLVMContext &Context, bool Lazy) {
25  SMDiagnostic Err;
26  ErrorOr<std::unique_ptr<Module>> ModuleOrErr(nullptr);
27  if (Lazy) {
28    ModuleOrErr =
29        getLazyBitcodeModule(MemoryBuffer::getMemBuffer(Buffer, false), Context,
30                             /* ShouldLazyLoadMetadata */ Lazy);
31  } else {
32    ModuleOrErr = parseBitcodeFile(Buffer, Context);
33  }
34  if (std::error_code EC = ModuleOrErr.getError()) {
35    Err = SMDiagnostic(Buffer.getBufferIdentifier(), SourceMgr::DK_Error,
36                       EC.message());
37    Err.print("ThinLTO", errs());
38    report_fatal_error("Can't load module, abort.");
39  }
40  return std::move(ModuleOrErr.get());
41}
42
43static void thinLTOResolveWeakForLinkerGUID(
44    GlobalValueSummaryList &GVSummaryList, GlobalValue::GUID GUID,
45    DenseSet<GlobalValueSummary *> &GlobalInvolvedWithAlias,
46    function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
47        isPrevailing,
48    function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
49        recordNewLinkage) {
50  for (auto &S : GVSummaryList) {
51    if (GlobalInvolvedWithAlias.count(S.get()))
52      continue;
53    GlobalValue::LinkageTypes OriginalLinkage = S->linkage();
54    if (!GlobalValue::isWeakForLinker(OriginalLinkage))
55      continue;
56    // We need to emit only one of these. The prevailing module will keep it,
57    // but turned into a weak, while the others will drop it when possible.
58    if (isPrevailing(GUID, S.get())) {
59      if (GlobalValue::isLinkOnceLinkage(OriginalLinkage))
60        S->setLinkage(GlobalValue::getWeakLinkage(
61            GlobalValue::isLinkOnceODRLinkage(OriginalLinkage)));
62    }
63    // Alias can't be turned into available_externally.
64    else if (!isa<AliasSummary>(S.get()) &&
65             (GlobalValue::isLinkOnceODRLinkage(OriginalLinkage) ||
66              GlobalValue::isWeakODRLinkage(OriginalLinkage)))
67      S->setLinkage(GlobalValue::AvailableExternallyLinkage);
68    if (S->linkage() != OriginalLinkage)
69      recordNewLinkage(S->modulePath(), GUID, S->linkage());
70  }
71}
72
73// Resolve Weak and LinkOnce values in the \p Index.
74//
75// We'd like to drop these functions if they are no longer referenced in the
76// current module. However there is a chance that another module is still
77// referencing them because of the import. We make sure we always emit at least
78// one copy.
79void thinLTOResolveWeakForLinkerInIndex(
80    ModuleSummaryIndex &Index,
81    function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
82        isPrevailing,
83    function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
84        recordNewLinkage) {
85  // We won't optimize the globals that are referenced by an alias for now
86  // Ideally we should turn the alias into a global and duplicate the definition
87  // when needed.
88  DenseSet<GlobalValueSummary *> GlobalInvolvedWithAlias;
89  for (auto &I : Index)
90    for (auto &S : I.second)
91      if (auto AS = dyn_cast<AliasSummary>(S.get()))
92        GlobalInvolvedWithAlias.insert(&AS->getAliasee());
93
94  for (auto &I : Index)
95    thinLTOResolveWeakForLinkerGUID(I.second, I.first, GlobalInvolvedWithAlias,
96                                    isPrevailing, recordNewLinkage);
97}
98
99static void thinLTOInternalizeAndPromoteGUID(
100    GlobalValueSummaryList &GVSummaryList, GlobalValue::GUID GUID,
101    function_ref<bool(StringRef, GlobalValue::GUID)> isExported) {
102  for (auto &S : GVSummaryList) {
103    if (isExported(S->modulePath(), GUID)) {
104      if (GlobalValue::isLocalLinkage(S->linkage()))
105        S->setLinkage(GlobalValue::ExternalLinkage);
106    } else if (!GlobalValue::isLocalLinkage(S->linkage()))
107      S->setLinkage(GlobalValue::InternalLinkage);
108  }
109}
110
111// Update the linkages in the given \p Index to mark exported values
112// as external and non-exported values as internal.
113void thinLTOInternalizeAndPromoteInIndex(
114    ModuleSummaryIndex &Index,
115    function_ref<bool(StringRef, GlobalValue::GUID)> isExported) {
116  for (auto &I : Index)
117    thinLTOInternalizeAndPromoteGUID(I.second, I.first, isExported);
118}
119}
120