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/AliasAnalysis.h"
19 #include "llvm/Analysis/CGSCCPassManager.h"
20 #include "llvm/Analysis/TargetLibraryInfo.h"
21 #include "llvm/Analysis/TargetTransformInfo.h"
22 #include "llvm/Bitcode/BitcodeReader.h"
23 #include "llvm/Bitcode/BitcodeWriter.h"
24 #include "llvm/IR/LegacyPassManager.h"
25 #include "llvm/IR/PassManager.h"
26 #include "llvm/IR/Verifier.h"
27 #include "llvm/LTO/LTO.h"
28 #include "llvm/MC/SubtargetFeature.h"
29 #include "llvm/Object/ModuleSymbolTable.h"
30 #include "llvm/Passes/PassBuilder.h"
31 #include "llvm/Support/Error.h"
32 #include "llvm/Support/FileSystem.h"
33 #include "llvm/Support/TargetRegistry.h"
34 #include "llvm/Support/ThreadPool.h"
35 #include "llvm/Target/TargetMachine.h"
36 #include "llvm/Transforms/IPO.h"
37 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
38 #include "llvm/Transforms/Scalar/LoopPassManager.h"
39 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
40 #include "llvm/Transforms/Utils/SplitModule.h"
41 
42 using namespace llvm;
43 using namespace lto;
44 
45 LLVM_ATTRIBUTE_NORETURN static void reportOpenError(StringRef Path, Twine Msg) {
46   errs() << "failed to open " << Path << ": " << Msg << '\n';
47   errs().flush();
48   exit(1);
49 }
50 
51 Error Config::addSaveTemps(std::string OutputFileName,
52                            bool UseInputModulePath) {
53   ShouldDiscardValueNames = false;
54 
55   std::error_code EC;
56   ResolutionFile = llvm::make_unique<raw_fd_ostream>(
57       OutputFileName + "resolution.txt", EC, sys::fs::OpenFlags::F_Text);
58   if (EC)
59     return errorCodeToError(EC);
60 
61   auto setHook = [&](std::string PathSuffix, ModuleHookFn &Hook) {
62     // Keep track of the hook provided by the linker, which also needs to run.
63     ModuleHookFn LinkerHook = Hook;
64     Hook = [=](unsigned Task, const Module &M) {
65       // If the linker's hook returned false, we need to pass that result
66       // through.
67       if (LinkerHook && !LinkerHook(Task, M))
68         return false;
69 
70       std::string PathPrefix;
71       // If this is the combined module (not a ThinLTO backend compile) or the
72       // user hasn't requested using the input module's path, emit to a file
73       // named from the provided OutputFileName with the Task ID appended.
74       if (M.getModuleIdentifier() == "ld-temp.o" || !UseInputModulePath) {
75         PathPrefix = OutputFileName + utostr(Task);
76       } else
77         PathPrefix = M.getModuleIdentifier();
78       std::string Path = PathPrefix + "." + PathSuffix + ".bc";
79       std::error_code EC;
80       raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
81       // Because -save-temps is a debugging feature, we report the error
82       // directly and exit.
83       if (EC)
84         reportOpenError(Path, EC.message());
85       WriteBitcodeToFile(&M, OS, /*ShouldPreserveUseListOrder=*/false);
86       return true;
87     };
88   };
89 
90   setHook("0.preopt", PreOptModuleHook);
91   setHook("1.promote", PostPromoteModuleHook);
92   setHook("2.internalize", PostInternalizeModuleHook);
93   setHook("3.import", PostImportModuleHook);
94   setHook("4.opt", PostOptModuleHook);
95   setHook("5.precodegen", PreCodeGenModuleHook);
96 
97   CombinedIndexHook = [=](const ModuleSummaryIndex &Index) {
98     std::string Path = OutputFileName + "index.bc";
99     std::error_code EC;
100     raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
101     // Because -save-temps is a debugging feature, we report the error
102     // directly and exit.
103     if (EC)
104       reportOpenError(Path, EC.message());
105     WriteIndexToFile(Index, OS);
106 
107     Path = OutputFileName + "index.dot";
108     raw_fd_ostream OSDot(Path, EC, sys::fs::OpenFlags::F_None);
109     if (EC)
110       reportOpenError(Path, EC.message());
111     Index.exportToDot(OSDot);
112     return true;
113   };
114 
115   return Error::success();
116 }
117 
118 namespace {
119 
120 std::unique_ptr<TargetMachine>
121 createTargetMachine(Config &Conf, const Target *TheTarget, Module &M) {
122   StringRef TheTriple = M.getTargetTriple();
123   SubtargetFeatures Features;
124   Features.getDefaultSubtargetFeatures(Triple(TheTriple));
125   for (const std::string &A : Conf.MAttrs)
126     Features.AddFeature(A);
127 
128   Reloc::Model RelocModel;
129   if (Conf.RelocModel)
130     RelocModel = *Conf.RelocModel;
131   else
132     RelocModel =
133         M.getPICLevel() == PICLevel::NotPIC ? Reloc::Static : Reloc::PIC_;
134 
135   return std::unique_ptr<TargetMachine>(TheTarget->createTargetMachine(
136       TheTriple, Conf.CPU, Features.getString(), Conf.Options, RelocModel,
137       Conf.CodeModel, Conf.CGOptLevel));
138 }
139 
140 static void runNewPMPasses(Config &Conf, Module &Mod, TargetMachine *TM,
141                            unsigned OptLevel, bool IsThinLTO) {
142   Optional<PGOOptions> PGOOpt;
143   if (!Conf.SampleProfile.empty())
144     PGOOpt = PGOOptions("", "", Conf.SampleProfile, false, true);
145 
146   PassBuilder PB(TM, PGOOpt);
147   AAManager AA;
148 
149   // Parse a custom AA pipeline if asked to.
150   if (!PB.parseAAPipeline(AA, "default"))
151     report_fatal_error("Error parsing default AA pipeline");
152 
153   LoopAnalysisManager LAM(Conf.DebugPassManager);
154   FunctionAnalysisManager FAM(Conf.DebugPassManager);
155   CGSCCAnalysisManager CGAM(Conf.DebugPassManager);
156   ModuleAnalysisManager MAM(Conf.DebugPassManager);
157 
158   // Register the AA manager first so that our version is the one used.
159   FAM.registerPass([&] { return std::move(AA); });
160 
161   // Register all the basic analyses with the managers.
162   PB.registerModuleAnalyses(MAM);
163   PB.registerCGSCCAnalyses(CGAM);
164   PB.registerFunctionAnalyses(FAM);
165   PB.registerLoopAnalyses(LAM);
166   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
167 
168   ModulePassManager MPM(Conf.DebugPassManager);
169   // FIXME (davide): verify the input.
170 
171   PassBuilder::OptimizationLevel OL;
172 
173   switch (OptLevel) {
174   default:
175     llvm_unreachable("Invalid optimization level");
176   case 0:
177     OL = PassBuilder::O0;
178     break;
179   case 1:
180     OL = PassBuilder::O1;
181     break;
182   case 2:
183     OL = PassBuilder::O2;
184     break;
185   case 3:
186     OL = PassBuilder::O3;
187     break;
188   }
189 
190   if (IsThinLTO)
191     MPM = PB.buildThinLTODefaultPipeline(OL, Conf.DebugPassManager);
192   else
193     MPM = PB.buildLTODefaultPipeline(OL, Conf.DebugPassManager);
194   MPM.run(Mod, MAM);
195 
196   // FIXME (davide): verify the output.
197 }
198 
199 static void runNewPMCustomPasses(Module &Mod, TargetMachine *TM,
200                                  std::string PipelineDesc,
201                                  std::string AAPipelineDesc,
202                                  bool DisableVerify) {
203   PassBuilder PB(TM);
204   AAManager AA;
205 
206   // Parse a custom AA pipeline if asked to.
207   if (!AAPipelineDesc.empty())
208     if (!PB.parseAAPipeline(AA, AAPipelineDesc))
209       report_fatal_error("unable to parse AA pipeline description: " +
210                          AAPipelineDesc);
211 
212   LoopAnalysisManager LAM;
213   FunctionAnalysisManager FAM;
214   CGSCCAnalysisManager CGAM;
215   ModuleAnalysisManager MAM;
216 
217   // Register the AA manager first so that our version is the one used.
218   FAM.registerPass([&] { return std::move(AA); });
219 
220   // Register all the basic analyses with the managers.
221   PB.registerModuleAnalyses(MAM);
222   PB.registerCGSCCAnalyses(CGAM);
223   PB.registerFunctionAnalyses(FAM);
224   PB.registerLoopAnalyses(LAM);
225   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
226 
227   ModulePassManager MPM;
228 
229   // Always verify the input.
230   MPM.addPass(VerifierPass());
231 
232   // Now, add all the passes we've been requested to.
233   if (!PB.parsePassPipeline(MPM, PipelineDesc))
234     report_fatal_error("unable to parse pass pipeline description: " +
235                        PipelineDesc);
236 
237   if (!DisableVerify)
238     MPM.addPass(VerifierPass());
239   MPM.run(Mod, MAM);
240 }
241 
242 static void runOldPMPasses(Config &Conf, Module &Mod, TargetMachine *TM,
243                            bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
244                            const ModuleSummaryIndex *ImportSummary) {
245   legacy::PassManager passes;
246   passes.add(createTargetTransformInfoWrapperPass(TM->getTargetIRAnalysis()));
247 
248   PassManagerBuilder PMB;
249   PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM->getTargetTriple()));
250   PMB.Inliner = createFunctionInliningPass();
251   PMB.ExportSummary = ExportSummary;
252   PMB.ImportSummary = ImportSummary;
253   // Unconditionally verify input since it is not verified before this
254   // point and has unknown origin.
255   PMB.VerifyInput = true;
256   PMB.VerifyOutput = !Conf.DisableVerify;
257   PMB.LoopVectorize = true;
258   PMB.SLPVectorize = true;
259   PMB.OptLevel = Conf.OptLevel;
260   PMB.PGOSampleUse = Conf.SampleProfile;
261   if (IsThinLTO)
262     PMB.populateThinLTOPassManager(passes);
263   else
264     PMB.populateLTOPassManager(passes);
265   passes.run(Mod);
266 }
267 
268 bool opt(Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
269          bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
270          const ModuleSummaryIndex *ImportSummary) {
271   // FIXME: Plumb the combined index into the new pass manager.
272   if (!Conf.OptPipeline.empty())
273     runNewPMCustomPasses(Mod, TM, Conf.OptPipeline, Conf.AAPipeline,
274                          Conf.DisableVerify);
275   else if (Conf.UseNewPM)
276     runNewPMPasses(Conf, Mod, TM, Conf.OptLevel, IsThinLTO);
277   else
278     runOldPMPasses(Conf, Mod, TM, IsThinLTO, ExportSummary, ImportSummary);
279   return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
280 }
281 
282 void codegen(Config &Conf, TargetMachine *TM, AddStreamFn AddStream,
283              unsigned Task, Module &Mod) {
284   if (Conf.PreCodeGenModuleHook && !Conf.PreCodeGenModuleHook(Task, Mod))
285     return;
286 
287   auto Stream = AddStream(Task);
288   legacy::PassManager CodeGenPasses;
289   if (TM->addPassesToEmitFile(CodeGenPasses, *Stream->OS, Conf.CGFileType))
290     report_fatal_error("Failed to setup codegen");
291   CodeGenPasses.run(Mod);
292 }
293 
294 void splitCodeGen(Config &C, TargetMachine *TM, AddStreamFn AddStream,
295                   unsigned ParallelCodeGenParallelismLevel,
296                   std::unique_ptr<Module> Mod) {
297   ThreadPool CodegenThreadPool(ParallelCodeGenParallelismLevel);
298   unsigned ThreadCount = 0;
299   const Target *T = &TM->getTarget();
300 
301   SplitModule(
302       std::move(Mod), ParallelCodeGenParallelismLevel,
303       [&](std::unique_ptr<Module> MPart) {
304         // We want to clone the module in a new context to multi-thread the
305         // codegen. We do it by serializing partition modules to bitcode
306         // (while still on the main thread, in order to avoid data races) and
307         // spinning up new threads which deserialize the partitions into
308         // separate contexts.
309         // FIXME: Provide a more direct way to do this in LLVM.
310         SmallString<0> BC;
311         raw_svector_ostream BCOS(BC);
312         WriteBitcodeToFile(MPart.get(), BCOS);
313 
314         // Enqueue the task
315         CodegenThreadPool.async(
316             [&](const SmallString<0> &BC, unsigned ThreadId) {
317               LTOLLVMContext Ctx(C);
318               Expected<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
319                   MemoryBufferRef(StringRef(BC.data(), BC.size()), "ld-temp.o"),
320                   Ctx);
321               if (!MOrErr)
322                 report_fatal_error("Failed to read bitcode");
323               std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
324 
325               std::unique_ptr<TargetMachine> TM =
326                   createTargetMachine(C, T, *MPartInCtx);
327 
328               codegen(C, TM.get(), AddStream, ThreadId, *MPartInCtx);
329             },
330             // Pass BC using std::move to ensure that it get moved rather than
331             // copied into the thread's context.
332             std::move(BC), ThreadCount++);
333       },
334       false);
335 
336   // Because the inner lambda (which runs in a worker thread) captures our local
337   // variables, we need to wait for the worker threads to terminate before we
338   // can leave the function scope.
339   CodegenThreadPool.wait();
340 }
341 
342 Expected<const Target *> initAndLookupTarget(Config &C, Module &Mod) {
343   if (!C.OverrideTriple.empty())
344     Mod.setTargetTriple(C.OverrideTriple);
345   else if (Mod.getTargetTriple().empty())
346     Mod.setTargetTriple(C.DefaultTriple);
347 
348   std::string Msg;
349   const Target *T = TargetRegistry::lookupTarget(Mod.getTargetTriple(), Msg);
350   if (!T)
351     return make_error<StringError>(Msg, inconvertibleErrorCode());
352   return T;
353 }
354 
355 }
356 
357 static void
358 finalizeOptimizationRemarks(std::unique_ptr<ToolOutputFile> DiagOutputFile) {
359   // Make sure we flush the diagnostic remarks file in case the linker doesn't
360   // call the global destructors before exiting.
361   if (!DiagOutputFile)
362     return;
363   DiagOutputFile->keep();
364   DiagOutputFile->os().flush();
365 }
366 
367 Error lto::backend(Config &C, AddStreamFn AddStream,
368                    unsigned ParallelCodeGenParallelismLevel,
369                    std::unique_ptr<Module> Mod,
370                    ModuleSummaryIndex &CombinedIndex) {
371   Expected<const Target *> TOrErr = initAndLookupTarget(C, *Mod);
372   if (!TOrErr)
373     return TOrErr.takeError();
374 
375   std::unique_ptr<TargetMachine> TM = createTargetMachine(C, *TOrErr, *Mod);
376 
377   // Setup optimization remarks.
378   auto DiagFileOrErr = lto::setupOptimizationRemarks(
379       Mod->getContext(), C.RemarksFilename, C.RemarksWithHotness);
380   if (!DiagFileOrErr)
381     return DiagFileOrErr.takeError();
382   auto DiagnosticOutputFile = std::move(*DiagFileOrErr);
383 
384   if (!C.CodeGenOnly) {
385     if (!opt(C, TM.get(), 0, *Mod, /*IsThinLTO=*/false,
386              /*ExportSummary=*/&CombinedIndex, /*ImportSummary=*/nullptr)) {
387       finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
388       return Error::success();
389     }
390   }
391 
392   if (ParallelCodeGenParallelismLevel == 1) {
393     codegen(C, TM.get(), AddStream, 0, *Mod);
394   } else {
395     splitCodeGen(C, TM.get(), AddStream, ParallelCodeGenParallelismLevel,
396                  std::move(Mod));
397   }
398   finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
399   return Error::success();
400 }
401 
402 Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,
403                        Module &Mod, const ModuleSummaryIndex &CombinedIndex,
404                        const FunctionImporter::ImportMapTy &ImportList,
405                        const GVSummaryMapTy &DefinedGlobals,
406                        MapVector<StringRef, BitcodeModule> &ModuleMap) {
407   Expected<const Target *> TOrErr = initAndLookupTarget(Conf, Mod);
408   if (!TOrErr)
409     return TOrErr.takeError();
410 
411   std::unique_ptr<TargetMachine> TM = createTargetMachine(Conf, *TOrErr, Mod);
412 
413   if (Conf.CodeGenOnly) {
414     codegen(Conf, TM.get(), AddStream, Task, Mod);
415     return Error::success();
416   }
417 
418   if (Conf.PreOptModuleHook && !Conf.PreOptModuleHook(Task, Mod))
419     return Error::success();
420 
421   renameModuleForThinLTO(Mod, CombinedIndex);
422 
423   thinLTOResolveWeakForLinkerModule(Mod, DefinedGlobals);
424 
425   if (Conf.PostPromoteModuleHook && !Conf.PostPromoteModuleHook(Task, Mod))
426     return Error::success();
427 
428   if (!DefinedGlobals.empty())
429     thinLTOInternalizeModule(Mod, DefinedGlobals);
430 
431   if (Conf.PostInternalizeModuleHook &&
432       !Conf.PostInternalizeModuleHook(Task, Mod))
433     return Error::success();
434 
435   auto ModuleLoader = [&](StringRef Identifier) {
436     assert(Mod.getContext().isODRUniquingDebugTypes() &&
437            "ODR Type uniquing should be enabled on the context");
438     auto I = ModuleMap.find(Identifier);
439     assert(I != ModuleMap.end());
440     return I->second.getLazyModule(Mod.getContext(),
441                                    /*ShouldLazyLoadMetadata=*/true,
442                                    /*IsImporting*/ true);
443   };
444 
445   FunctionImporter Importer(CombinedIndex, ModuleLoader);
446   if (Error Err = Importer.importFunctions(Mod, ImportList).takeError())
447     return Err;
448 
449   if (Conf.PostImportModuleHook && !Conf.PostImportModuleHook(Task, Mod))
450     return Error::success();
451 
452   if (!opt(Conf, TM.get(), Task, Mod, /*IsThinLTO=*/true,
453            /*ExportSummary=*/nullptr, /*ImportSummary=*/&CombinedIndex))
454     return Error::success();
455 
456   codegen(Conf, TM.get(), AddStream, Task, Mod);
457   return Error::success();
458 }
459