1 //===- LTO.cpp ------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "LTO.h"
10 #include "Config.h"
11 #include "InputFiles.h"
12 #include "Symbols.h"
13 #include "lld/Common/Args.h"
14 #include "lld/Common/ErrorHandler.h"
15 #include "lld/Common/Strings.h"
16 #include "lld/Common/TargetOptionsCommandFlags.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/ADT/SmallString.h"
19 #include "llvm/ADT/StringRef.h"
20 #include "llvm/ADT/Twine.h"
21 #include "llvm/IR/DiagnosticPrinter.h"
22 #include "llvm/LTO/Config.h"
23 #include "llvm/LTO/LTO.h"
24 #include "llvm/Object/SymbolicFile.h"
25 #include "llvm/Support/Caching.h"
26 #include "llvm/Support/CodeGen.h"
27 #include "llvm/Support/Error.h"
28 #include "llvm/Support/FileSystem.h"
29 #include "llvm/Support/MemoryBuffer.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include <algorithm>
32 #include <cstddef>
33 #include <memory>
34 #include <string>
35 #include <system_error>
36 #include <vector>
37
38 using namespace llvm;
39
40 namespace lld {
41 namespace wasm {
createLTO()42 static std::unique_ptr<lto::LTO> createLTO() {
43 lto::Config c;
44 c.Options = initTargetOptionsFromCodeGenFlags();
45
46 // Always emit a section per function/data with LTO.
47 c.Options.FunctionSections = true;
48 c.Options.DataSections = true;
49
50 c.DisableVerify = config->disableVerify;
51 c.DiagHandler = diagnosticHandler;
52 c.OptLevel = config->ltoo;
53 c.MAttrs = getMAttrs();
54 c.CGOptLevel = args::getCGOptLevel(config->ltoo);
55 c.DebugPassManager = config->ltoDebugPassManager;
56
57 if (config->relocatable)
58 c.RelocModel = None;
59 else if (config->isPic)
60 c.RelocModel = Reloc::PIC_;
61 else
62 c.RelocModel = Reloc::Static;
63
64 if (config->saveTemps)
65 checkError(c.addSaveTemps(config->outputFile.str() + ".",
66 /*UseInputModulePath*/ true));
67 lto::ThinBackend backend = lto::createInProcessThinBackend(
68 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs));
69 return std::make_unique<lto::LTO>(std::move(c), backend,
70 config->ltoPartitions);
71 }
72
BitcodeCompiler()73 BitcodeCompiler::BitcodeCompiler() : ltoObj(createLTO()) {}
74
75 BitcodeCompiler::~BitcodeCompiler() = default;
76
undefine(Symbol * s)77 static void undefine(Symbol *s) {
78 if (auto f = dyn_cast<DefinedFunction>(s))
79 replaceSymbol<UndefinedFunction>(f, f->getName(), None, None, 0,
80 f->getFile(), f->signature);
81 else if (isa<DefinedData>(s))
82 replaceSymbol<UndefinedData>(s, s->getName(), 0, s->getFile());
83 else
84 llvm_unreachable("unexpected symbol kind");
85 }
86
add(BitcodeFile & f)87 void BitcodeCompiler::add(BitcodeFile &f) {
88 lto::InputFile &obj = *f.obj;
89 unsigned symNum = 0;
90 ArrayRef<Symbol *> syms = f.getSymbols();
91 std::vector<lto::SymbolResolution> resols(syms.size());
92
93 // Provide a resolution to the LTO API for each symbol.
94 for (const lto::InputFile::Symbol &objSym : obj.symbols()) {
95 Symbol *sym = syms[symNum];
96 lto::SymbolResolution &r = resols[symNum];
97 ++symNum;
98
99 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
100 // reports two symbols for module ASM defined. Without this check, lld
101 // flags an undefined in IR with a definition in ASM as prevailing.
102 // Once IRObjectFile is fixed to report only one symbol this hack can
103 // be removed.
104 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f;
105 r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj ||
106 sym->isNoStrip() ||
107 (r.Prevailing && sym->isExported());
108 if (r.Prevailing)
109 undefine(sym);
110
111 // We tell LTO to not apply interprocedural optimization for wrapped
112 // (with --wrap) symbols because otherwise LTO would inline them while
113 // their values are still not final.
114 r.LinkerRedefined = !sym->canInline;
115 }
116 checkError(ltoObj->add(std::move(f.obj), resols));
117 }
118
119 // Merge all the bitcode files we have seen, codegen the result
120 // and return the resulting objects.
compile()121 std::vector<StringRef> BitcodeCompiler::compile() {
122 unsigned maxTasks = ltoObj->getMaxTasks();
123 buf.resize(maxTasks);
124 files.resize(maxTasks);
125
126 // The --thinlto-cache-dir option specifies the path to a directory in which
127 // to cache native object files for ThinLTO incremental builds. If a path was
128 // specified, configure LTO to use it as the cache directory.
129 FileCache cache;
130 if (!config->thinLTOCacheDir.empty())
131 cache =
132 check(localCache("ThinLTO", "Thin", config->thinLTOCacheDir,
133 [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
134 files[task] = std::move(mb);
135 }));
136
137 checkError(ltoObj->run(
138 [&](size_t task) {
139 return std::make_unique<CachedFileStream>(
140 std::make_unique<raw_svector_ostream>(buf[task]));
141 },
142 cache));
143
144 if (!config->thinLTOCacheDir.empty())
145 pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy);
146
147 std::vector<StringRef> ret;
148 for (unsigned i = 0; i != maxTasks; ++i) {
149 if (buf[i].empty())
150 continue;
151 if (config->saveTemps) {
152 if (i == 0)
153 saveBuffer(buf[i], config->outputFile + ".lto.o");
154 else
155 saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o");
156 }
157 ret.emplace_back(buf[i].data(), buf[i].size());
158 }
159
160 for (std::unique_ptr<MemoryBuffer> &file : files)
161 if (file)
162 ret.push_back(file->getBuffer());
163
164 return ret;
165 }
166
167 } // namespace wasm
168 } // namespace lld
169