1 //===-LTOBackend.cpp - LLVM Link Time Optimizer Backend -------------------===//
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 the "backend" phase of LTO, i.e. it performs
11 // optimization and code generation on a loaded module. It is generally used
12 // internally by the LTO class but can also be used independently, for example
13 // to implement a standalone ThinLTO backend.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "llvm/LTO/LTOBackend.h"
18 #include "llvm/Analysis/TargetLibraryInfo.h"
19 #include "llvm/Analysis/TargetTransformInfo.h"
20 #include "llvm/Bitcode/ReaderWriter.h"
21 #include "llvm/IR/LegacyPassManager.h"
22 #include "llvm/LTO/LTO.h"
23 #include "llvm/MC/SubtargetFeature.h"
24 #include "llvm/Support/Error.h"
25 #include "llvm/Support/FileSystem.h"
26 #include "llvm/Support/TargetRegistry.h"
27 #include "llvm/Support/ThreadPool.h"
28 #include "llvm/Target/TargetMachine.h"
29 #include "llvm/Transforms/IPO.h"
30 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
31 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
32 #include "llvm/Transforms/Utils/SplitModule.h"
33 
34 using namespace llvm;
35 using namespace lto;
36 
37 Error Config::addSaveTemps(std::string OutputFileName,
38                            bool UseInputModulePath) {
39   ShouldDiscardValueNames = false;
40 
41   std::error_code EC;
42   ResolutionFile = llvm::make_unique<raw_fd_ostream>(
43       OutputFileName + ".resolution.txt", EC, sys::fs::OpenFlags::F_Text);
44   if (EC)
45     return errorCodeToError(EC);
46 
47   auto setHook = [&](std::string PathSuffix, ModuleHookFn &Hook) {
48     // Keep track of the hook provided by the linker, which also needs to run.
49     ModuleHookFn LinkerHook = Hook;
50     Hook = [=](unsigned Task, Module &M) {
51       // If the linker's hook returned false, we need to pass that result
52       // through.
53       if (LinkerHook && !LinkerHook(Task, M))
54         return false;
55 
56       std::string PathPrefix;
57       // If this is the combined module (not a ThinLTO backend compile) or the
58       // user hasn't requested using the input module's path, emit to a file
59       // named from the provided OutputFileName with the Task ID appended.
60       if (M.getModuleIdentifier() == "ld-temp.o" || !UseInputModulePath) {
61         PathPrefix = OutputFileName;
62         if (Task != 0)
63           PathPrefix += "." + utostr(Task);
64       } else
65         PathPrefix = M.getModuleIdentifier();
66       std::string Path = PathPrefix + "." + PathSuffix + ".bc";
67       std::error_code EC;
68       raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
69       if (EC) {
70         // Because -save-temps is a debugging feature, we report the error
71         // directly and exit.
72         llvm::errs() << "failed to open " << Path << ": " << EC.message()
73                      << '\n';
74         exit(1);
75       }
76       WriteBitcodeToFile(&M, OS, /*ShouldPreserveUseListOrder=*/false);
77       return true;
78     };
79   };
80 
81   setHook("0.preopt", PreOptModuleHook);
82   setHook("1.promote", PostPromoteModuleHook);
83   setHook("2.internalize", PostInternalizeModuleHook);
84   setHook("3.import", PostImportModuleHook);
85   setHook("4.opt", PostOptModuleHook);
86   setHook("5.precodegen", PreCodeGenModuleHook);
87 
88   CombinedIndexHook = [=](const ModuleSummaryIndex &Index) {
89     std::string Path = OutputFileName + ".index.bc";
90     std::error_code EC;
91     raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
92     if (EC) {
93       // Because -save-temps is a debugging feature, we report the error
94       // directly and exit.
95       llvm::errs() << "failed to open " << Path << ": " << EC.message() << '\n';
96       exit(1);
97     }
98     WriteIndexToFile(Index, OS);
99     return true;
100   };
101 
102   return Error();
103 }
104 
105 namespace {
106 
107 std::unique_ptr<TargetMachine>
108 createTargetMachine(Config &C, StringRef TheTriple, const Target *TheTarget) {
109   SubtargetFeatures Features;
110   Features.getDefaultSubtargetFeatures(Triple(TheTriple));
111   for (const std::string &A : C.MAttrs)
112     Features.AddFeature(A);
113 
114   return std::unique_ptr<TargetMachine>(TheTarget->createTargetMachine(
115       TheTriple, C.CPU, Features.getString(), C.Options, C.RelocModel,
116       C.CodeModel, C.CGOptLevel));
117 }
118 
119 bool opt(Config &C, TargetMachine *TM, unsigned Task, Module &M,
120          bool IsThinLto) {
121   M.setDataLayout(TM->createDataLayout());
122 
123   legacy::PassManager passes;
124   passes.add(createTargetTransformInfoWrapperPass(TM->getTargetIRAnalysis()));
125 
126   PassManagerBuilder PMB;
127   PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM->getTargetTriple()));
128   PMB.Inliner = createFunctionInliningPass();
129   // Unconditionally verify input since it is not verified before this
130   // point and has unknown origin.
131   PMB.VerifyInput = true;
132   PMB.VerifyOutput = !C.DisableVerify;
133   PMB.LoopVectorize = true;
134   PMB.SLPVectorize = true;
135   PMB.OptLevel = C.OptLevel;
136   if (IsThinLto)
137     PMB.populateThinLTOPassManager(passes);
138   else
139     PMB.populateLTOPassManager(passes);
140   passes.run(M);
141 
142   if (C.PostOptModuleHook && !C.PostOptModuleHook(Task, M))
143     return false;
144 
145   return true;
146 }
147 
148 void codegen(Config &C, TargetMachine *TM, AddOutputFn AddOutput, unsigned Task,
149              Module &M) {
150   if (C.PreCodeGenModuleHook && !C.PreCodeGenModuleHook(Task, M))
151     return;
152 
153   auto Output = AddOutput(Task);
154   std::unique_ptr<raw_pwrite_stream> OS = Output->getStream();
155   legacy::PassManager CodeGenPasses;
156   if (TM->addPassesToEmitFile(CodeGenPasses, *OS,
157                               TargetMachine::CGFT_ObjectFile))
158     report_fatal_error("Failed to setup codegen");
159   CodeGenPasses.run(M);
160 }
161 
162 void splitCodeGen(Config &C, TargetMachine *TM, AddOutputFn AddOutput,
163                   unsigned ParallelCodeGenParallelismLevel,
164                   std::unique_ptr<Module> M) {
165   ThreadPool CodegenThreadPool(ParallelCodeGenParallelismLevel);
166   unsigned ThreadCount = 0;
167   const Target *T = &TM->getTarget();
168 
169   SplitModule(
170       std::move(M), ParallelCodeGenParallelismLevel,
171       [&](std::unique_ptr<Module> MPart) {
172         // We want to clone the module in a new context to multi-thread the
173         // codegen. We do it by serializing partition modules to bitcode
174         // (while still on the main thread, in order to avoid data races) and
175         // spinning up new threads which deserialize the partitions into
176         // separate contexts.
177         // FIXME: Provide a more direct way to do this in LLVM.
178         SmallString<0> BC;
179         raw_svector_ostream BCOS(BC);
180         WriteBitcodeToFile(MPart.get(), BCOS);
181 
182         // Enqueue the task
183         CodegenThreadPool.async(
184             [&](const SmallString<0> &BC, unsigned ThreadId) {
185               LTOLLVMContext Ctx(C);
186               ErrorOr<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
187                   MemoryBufferRef(StringRef(BC.data(), BC.size()), "ld-temp.o"),
188                   Ctx);
189               if (!MOrErr)
190                 report_fatal_error("Failed to read bitcode");
191               std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
192 
193               std::unique_ptr<TargetMachine> TM =
194                   createTargetMachine(C, MPartInCtx->getTargetTriple(), T);
195               codegen(C, TM.get(), AddOutput, ThreadId, *MPartInCtx);
196             },
197             // Pass BC using std::move to ensure that it get moved rather than
198             // copied into the thread's context.
199             std::move(BC), ThreadCount++);
200       },
201       false);
202 }
203 
204 Expected<const Target *> initAndLookupTarget(Config &C, Module &M) {
205   if (!C.OverrideTriple.empty())
206     M.setTargetTriple(C.OverrideTriple);
207   else if (M.getTargetTriple().empty())
208     M.setTargetTriple(C.DefaultTriple);
209 
210   std::string Msg;
211   const Target *T = TargetRegistry::lookupTarget(M.getTargetTriple(), Msg);
212   if (!T)
213     return make_error<StringError>(Msg, inconvertibleErrorCode());
214   return T;
215 }
216 
217 }
218 
219 Error lto::backend(Config &C, AddOutputFn AddOutput,
220                    unsigned ParallelCodeGenParallelismLevel,
221                    std::unique_ptr<Module> M) {
222   Expected<const Target *> TOrErr = initAndLookupTarget(C, *M);
223   if (!TOrErr)
224     return TOrErr.takeError();
225 
226   std::unique_ptr<TargetMachine> TM =
227       createTargetMachine(C, M->getTargetTriple(), *TOrErr);
228 
229   if (!opt(C, TM.get(), 0, *M, /*IsThinLto=*/false))
230     return Error();
231 
232   if (ParallelCodeGenParallelismLevel == 1)
233     codegen(C, TM.get(), AddOutput, 0, *M);
234   else
235     splitCodeGen(C, TM.get(), AddOutput, ParallelCodeGenParallelismLevel,
236                  std::move(M));
237   return Error();
238 }
239 
240 Error lto::thinBackend(Config &Conf, unsigned Task, AddOutputFn AddOutput,
241                        Module &Mod, ModuleSummaryIndex &CombinedIndex,
242                        const FunctionImporter::ImportMapTy &ImportList,
243                        const GVSummaryMapTy &DefinedGlobals,
244                        MapVector<StringRef, MemoryBufferRef> &ModuleMap) {
245   Expected<const Target *> TOrErr = initAndLookupTarget(Conf, Mod);
246   if (!TOrErr)
247     return TOrErr.takeError();
248 
249   std::unique_ptr<TargetMachine> TM =
250       createTargetMachine(Conf, Mod.getTargetTriple(), *TOrErr);
251 
252   if (Conf.PreOptModuleHook && !Conf.PreOptModuleHook(Task, Mod))
253     return Error();
254 
255   thinLTOResolveWeakForLinkerModule(Mod, DefinedGlobals);
256 
257   renameModuleForThinLTO(Mod, CombinedIndex);
258 
259   if (Conf.PostPromoteModuleHook && !Conf.PostPromoteModuleHook(Task, Mod))
260     return Error();
261 
262   if (!DefinedGlobals.empty())
263     thinLTOInternalizeModule(Mod, DefinedGlobals);
264 
265   if (Conf.PostInternalizeModuleHook &&
266       !Conf.PostInternalizeModuleHook(Task, Mod))
267     return Error();
268 
269   auto ModuleLoader = [&](StringRef Identifier) {
270     return std::move(getLazyBitcodeModule(MemoryBuffer::getMemBuffer(
271                                               ModuleMap[Identifier], false),
272                                           Mod.getContext(),
273                                           /*ShouldLazyLoadMetadata=*/true)
274                          .get());
275   };
276 
277   FunctionImporter Importer(CombinedIndex, ModuleLoader);
278   Importer.importFunctions(Mod, ImportList);
279 
280   if (Conf.PostImportModuleHook && !Conf.PostImportModuleHook(Task, Mod))
281     return Error();
282 
283   if (!opt(Conf, TM.get(), Task, Mod, /*IsThinLto=*/true))
284     return Error();
285 
286   codegen(Conf, TM.get(), AddOutput, Task, Mod);
287   return Error();
288 }
289