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
20 namespace llvm {
21
22 // Simple helper to load a module from bitcode
loadModuleFromBuffer(const MemoryBufferRef & Buffer,LLVMContext & Context,bool Lazy)23 std::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
thinLTOResolveWeakForLinkerGUID(GlobalValueSummaryList & GVSummaryList,GlobalValue::GUID GUID,DenseSet<GlobalValueSummary * > & GlobalInvolvedWithAlias,function_ref<bool (GlobalValue::GUID,const GlobalValueSummary *)> isPrevailing,function_ref<void (StringRef,GlobalValue::GUID,GlobalValue::LinkageTypes)> recordNewLinkage)43 static 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.
thinLTOResolveWeakForLinkerInIndex(ModuleSummaryIndex & Index,function_ref<bool (GlobalValue::GUID,const GlobalValueSummary *)> isPrevailing,function_ref<void (StringRef,GlobalValue::GUID,GlobalValue::LinkageTypes)> recordNewLinkage)79 void 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
thinLTOInternalizeAndPromoteGUID(GlobalValueSummaryList & GVSummaryList,GlobalValue::GUID GUID,function_ref<bool (StringRef,GlobalValue::GUID)> isExported)99 static 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.
thinLTOInternalizeAndPromoteInIndex(ModuleSummaryIndex & Index,function_ref<bool (StringRef,GlobalValue::GUID)> isExported)113 void 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