1 //===- Delta.cpp - Delta Debugging Algorithm Implementation ---------------===//
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 // This file contains the implementation for the Delta Debugging Algorithm:
10 // it splits a given set of Targets (i.e. Functions, Instructions, BBs, etc.)
11 // into chunks and tries to reduce the number chunks that are interesting.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "Delta.h"
16 #include "ReducerWorkItem.h"
17 #include "TestRunner.h"
18 #include "Utils.h"
19 #include "llvm/ADT/STLExtras.h"
20 #include "llvm/Analysis/ModuleSummaryAnalysis.h"
21 #include "llvm/Analysis/ProfileSummaryInfo.h"
22 #include "llvm/Bitcode/BitcodeReader.h"
23 #include "llvm/Bitcode/BitcodeWriter.h"
24 #include "llvm/CodeGen/MachineFunction.h"
25 #include "llvm/IR/Module.h"
26 #include "llvm/IR/Verifier.h"
27 #include "llvm/MC/TargetRegistry.h"
28 #include "llvm/Support/CommandLine.h"
29 #include "llvm/Support/MemoryBufferRef.h"
30 #include "llvm/Support/ThreadPool.h"
31 #include <fstream>
32 #include <set>
33
34 using namespace llvm;
35
36 extern cl::OptionCategory LLVMReduceOptions;
37
38 static cl::opt<bool> AbortOnInvalidReduction(
39 "abort-on-invalid-reduction",
40 cl::desc("Abort if any reduction results in invalid IR"),
41 cl::cat(LLVMReduceOptions));
42
43 static cl::opt<unsigned int> StartingGranularityLevel(
44 "starting-granularity-level",
45 cl::desc("Number of times to divide chunks prior to first test"),
46 cl::cat(LLVMReduceOptions));
47
48 #ifdef LLVM_ENABLE_THREADS
49 static cl::opt<unsigned> NumJobs(
50 "j",
51 cl::desc("Maximum number of threads to use to process chunks. Set to 1 to "
52 "disable parallelism."),
53 cl::init(1), cl::cat(LLVMReduceOptions));
54 #else
55 unsigned NumJobs = 1;
56 #endif
57
58 /// Splits Chunks in half and prints them.
59 /// If unable to split (when chunk size is 1) returns false.
increaseGranularity(std::vector<Chunk> & Chunks)60 static bool increaseGranularity(std::vector<Chunk> &Chunks) {
61 if (Verbose)
62 errs() << "Increasing granularity...";
63 std::vector<Chunk> NewChunks;
64 bool SplitAny = false;
65
66 for (Chunk C : Chunks) {
67 if (C.End - C.Begin == 0)
68 NewChunks.push_back(C);
69 else {
70 int Half = (C.Begin + C.End) / 2;
71 NewChunks.push_back({C.Begin, Half});
72 NewChunks.push_back({Half + 1, C.End});
73 SplitAny = true;
74 }
75 }
76 if (SplitAny) {
77 Chunks = NewChunks;
78 if (Verbose) {
79 errs() << "Success! " << NewChunks.size() << " New Chunks:\n";
80 for (auto C : Chunks) {
81 errs() << '\t';
82 C.print();
83 errs() << '\n';
84 }
85 }
86 }
87 return SplitAny;
88 }
89
90 // Check if \p ChunkToCheckForUninterestingness is interesting. Returns the
91 // modified module if the chunk resulted in a reduction.
92 static std::unique_ptr<ReducerWorkItem>
CheckChunk(const Chunk ChunkToCheckForUninterestingness,std::unique_ptr<ReducerWorkItem> Clone,const TestRunner & Test,ReductionFunc ExtractChunksFromModule,const DenseSet<Chunk> & UninterestingChunks,const std::vector<Chunk> & ChunksStillConsideredInteresting)93 CheckChunk(const Chunk ChunkToCheckForUninterestingness,
94 std::unique_ptr<ReducerWorkItem> Clone, const TestRunner &Test,
95 ReductionFunc ExtractChunksFromModule,
96 const DenseSet<Chunk> &UninterestingChunks,
97 const std::vector<Chunk> &ChunksStillConsideredInteresting) {
98 // Take all of ChunksStillConsideredInteresting chunks, except those we've
99 // already deemed uninteresting (UninterestingChunks) but didn't remove
100 // from ChunksStillConsideredInteresting yet, and additionally ignore
101 // ChunkToCheckForUninterestingness chunk.
102 std::vector<Chunk> CurrentChunks;
103 CurrentChunks.reserve(ChunksStillConsideredInteresting.size() -
104 UninterestingChunks.size() - 1);
105 copy_if(ChunksStillConsideredInteresting, std::back_inserter(CurrentChunks),
106 [&](const Chunk &C) {
107 return C != ChunkToCheckForUninterestingness &&
108 !UninterestingChunks.count(C);
109 });
110
111 // Generate Module with only Targets inside Current Chunks
112 Oracle O(CurrentChunks);
113 ExtractChunksFromModule(O, *Clone);
114
115 // Some reductions may result in invalid IR. Skip such reductions.
116 if (Clone->verify(&errs())) {
117 if (AbortOnInvalidReduction) {
118 errs() << "Invalid reduction, aborting.\n";
119 Clone->print(errs());
120 exit(1);
121 }
122 if (Verbose) {
123 errs() << " **** WARNING | reduction resulted in invalid module, "
124 "skipping\n";
125 }
126 return nullptr;
127 }
128
129 if (Verbose) {
130 errs() << "Ignoring: ";
131 ChunkToCheckForUninterestingness.print();
132 for (const Chunk &C : UninterestingChunks)
133 C.print();
134 errs() << "\n";
135 }
136
137 if (!Clone->isReduced(Test)) {
138 // Program became non-reduced, so this chunk appears to be interesting.
139 if (Verbose)
140 errs() << "\n";
141 return nullptr;
142 }
143 return Clone;
144 }
145
ProcessChunkFromSerializedBitcode(const Chunk ChunkToCheckForUninterestingness,const TestRunner & Test,ReductionFunc ExtractChunksFromModule,const DenseSet<Chunk> & UninterestingChunks,ArrayRef<Chunk> ChunksStillConsideredInteresting,StringRef OriginalBC,std::atomic<bool> & AnyReduced)146 static SmallString<0> ProcessChunkFromSerializedBitcode(
147 const Chunk ChunkToCheckForUninterestingness, const TestRunner &Test,
148 ReductionFunc ExtractChunksFromModule,
149 const DenseSet<Chunk> &UninterestingChunks,
150 ArrayRef<Chunk> ChunksStillConsideredInteresting, StringRef OriginalBC,
151 std::atomic<bool> &AnyReduced) {
152 LLVMContext Ctx;
153 auto CloneMMM = std::make_unique<ReducerWorkItem>();
154 MemoryBufferRef Data(OriginalBC, "<bc file>");
155 CloneMMM->readBitcode(Data, Ctx, Test.getToolName());
156
157 SmallString<0> Result;
158 if (std::unique_ptr<ReducerWorkItem> ChunkResult =
159 CheckChunk(ChunkToCheckForUninterestingness, std::move(CloneMMM),
160 Test, ExtractChunksFromModule, UninterestingChunks,
161 ChunksStillConsideredInteresting)) {
162 raw_svector_ostream BCOS(Result);
163 ChunkResult->writeBitcode(BCOS);
164 // Communicate that the task reduced a chunk.
165 AnyReduced = true;
166 }
167 return Result;
168 }
169
170 using SharedTaskQueue = std::deque<std::shared_future<SmallString<0>>>;
171
waitAndDiscardResultsBarrier(SharedTaskQueue & TaskQueue)172 static void waitAndDiscardResultsBarrier(SharedTaskQueue &TaskQueue) {
173 while (!TaskQueue.empty()) {
174 auto &Future = TaskQueue.front();
175 Future.wait();
176 TaskQueue.pop_front();
177 }
178 }
179
180 /// Runs the Delta Debugging algorithm, splits the code into chunks and
181 /// reduces the amount of chunks that are considered interesting by the
182 /// given test. The number of chunks is determined by a preliminary run of the
183 /// reduction pass where no change must be made to the module.
runDeltaPass(TestRunner & Test,ReductionFunc ExtractChunksFromModule,StringRef Message)184 void llvm::runDeltaPass(TestRunner &Test, ReductionFunc ExtractChunksFromModule,
185 StringRef Message) {
186 assert(!Test.getProgram().verify(&errs()) &&
187 "input module is broken before making changes");
188 errs() << "*** " << Message << "...\n";
189
190 int Targets;
191 {
192 // Count the number of chunks by counting the number of calls to
193 // Oracle::shouldKeep() but always returning true so no changes are
194 // made.
195 std::vector<Chunk> AllChunks = {{0, INT_MAX}};
196 Oracle Counter(AllChunks);
197 ExtractChunksFromModule(Counter, Test.getProgram());
198 Targets = Counter.count();
199
200 assert(!Test.getProgram().verify(&errs()) &&
201 "input module is broken after counting chunks");
202 assert(Test.getProgram().isReduced(Test) &&
203 "input module no longer interesting after counting chunks");
204
205 #ifndef NDEBUG
206 // Make sure that the number of chunks does not change as we reduce.
207 std::vector<Chunk> NoChunks = {{0, INT_MAX}};
208 Oracle NoChunksCounter(NoChunks);
209 std::unique_ptr<ReducerWorkItem> Clone =
210 Test.getProgram().clone(Test.getTargetMachine());
211 ExtractChunksFromModule(NoChunksCounter, *Clone);
212 assert(Targets == NoChunksCounter.count() &&
213 "number of chunks changes when reducing");
214 #endif
215 }
216 if (!Targets) {
217 if (Verbose)
218 errs() << "\nNothing to reduce\n";
219 errs() << "----------------------------\n";
220 return;
221 }
222
223 std::vector<Chunk> ChunksStillConsideredInteresting = {{0, Targets - 1}};
224 std::unique_ptr<ReducerWorkItem> ReducedProgram;
225
226 for (unsigned int Level = 0; Level < StartingGranularityLevel; Level++) {
227 increaseGranularity(ChunksStillConsideredInteresting);
228 }
229
230 std::atomic<bool> AnyReduced;
231 std::unique_ptr<ThreadPool> ChunkThreadPoolPtr;
232 if (NumJobs > 1)
233 ChunkThreadPoolPtr =
234 std::make_unique<ThreadPool>(hardware_concurrency(NumJobs));
235
236 bool FoundAtLeastOneNewUninterestingChunkWithCurrentGranularity;
237 do {
238 FoundAtLeastOneNewUninterestingChunkWithCurrentGranularity = false;
239
240 DenseSet<Chunk> UninterestingChunks;
241
242 // When running with more than one thread, serialize the original bitcode
243 // to OriginalBC.
244 SmallString<0> OriginalBC;
245 if (NumJobs > 1) {
246 raw_svector_ostream BCOS(OriginalBC);
247 Test.getProgram().writeBitcode(BCOS);
248 }
249
250 SharedTaskQueue TaskQueue;
251 for (auto I = ChunksStillConsideredInteresting.rbegin(),
252 E = ChunksStillConsideredInteresting.rend();
253 I != E; ++I) {
254 std::unique_ptr<ReducerWorkItem> Result = nullptr;
255 unsigned WorkLeft = std::distance(I, E);
256
257 // Run in parallel mode, if the user requested more than one thread and
258 // there are at least a few chunks to process.
259 if (NumJobs > 1 && WorkLeft > 1) {
260 unsigned NumInitialTasks = std::min(WorkLeft, unsigned(NumJobs));
261 unsigned NumChunksProcessed = 0;
262
263 ThreadPool &ChunkThreadPool = *ChunkThreadPoolPtr;
264 TaskQueue.clear();
265
266 AnyReduced = false;
267 // Queue jobs to process NumInitialTasks chunks in parallel using
268 // ChunkThreadPool. When the tasks are added to the pool, parse the
269 // original module from OriginalBC with a fresh LLVMContext object. This
270 // ensures that the cloned module of each task uses an independent
271 // LLVMContext object. If a task reduces the input, serialize the result
272 // back in the corresponding Result element.
273 for (unsigned J = 0; J < NumInitialTasks; ++J) {
274 Chunk ChunkToCheck = *(I + J);
275 TaskQueue.emplace_back(ChunkThreadPool.async(
276 ProcessChunkFromSerializedBitcode, ChunkToCheck, std::ref(Test),
277 ExtractChunksFromModule, UninterestingChunks,
278 ChunksStillConsideredInteresting, OriginalBC,
279 std::ref(AnyReduced)));
280 }
281
282 // Start processing results of the queued tasks. We wait for the first
283 // task in the queue to finish. If it reduced a chunk, we parse the
284 // result and exit the loop.
285 // Otherwise we will try to schedule a new task, if
286 // * no other pending job reduced a chunk and
287 // * we have not reached the end of the chunk.
288 while (!TaskQueue.empty()) {
289 auto &Future = TaskQueue.front();
290 Future.wait();
291
292 NumChunksProcessed++;
293 SmallString<0> Res = Future.get();
294 TaskQueue.pop_front();
295 if (Res.empty()) {
296 unsigned NumScheduledTasks = NumChunksProcessed + TaskQueue.size();
297 if (!AnyReduced && I + NumScheduledTasks != E) {
298 Chunk ChunkToCheck = *(I + NumScheduledTasks);
299 TaskQueue.emplace_back(ChunkThreadPool.async(
300 ProcessChunkFromSerializedBitcode, ChunkToCheck,
301 std::ref(Test), ExtractChunksFromModule, UninterestingChunks,
302 ChunksStillConsideredInteresting, OriginalBC,
303 std::ref(AnyReduced)));
304 }
305 continue;
306 }
307
308 Result = std::make_unique<ReducerWorkItem>();
309 MemoryBufferRef Data(StringRef(Res), "<bc file>");
310 Result->readBitcode(Data, Test.getProgram().M->getContext(),
311 Test.getToolName());
312 break;
313 }
314
315 // If we broke out of the loop, we still need to wait for everything to
316 // avoid race access to the chunk set.
317 //
318 // TODO: Create a way to kill remaining items we're ignoring; they could
319 // take a long time.
320 waitAndDiscardResultsBarrier(TaskQueue);
321
322 // Forward I to the last chunk processed in parallel.
323 I += NumChunksProcessed - 1;
324 } else {
325 Result =
326 CheckChunk(*I, Test.getProgram().clone(Test.getTargetMachine()),
327 Test, ExtractChunksFromModule, UninterestingChunks,
328 ChunksStillConsideredInteresting);
329 }
330
331 if (!Result)
332 continue;
333
334 const Chunk ChunkToCheckForUninterestingness = *I;
335 FoundAtLeastOneNewUninterestingChunkWithCurrentGranularity = true;
336 UninterestingChunks.insert(ChunkToCheckForUninterestingness);
337 ReducedProgram = std::move(Result);
338
339 // FIXME: Report meaningful progress info
340 Test.writeOutput(" **** SUCCESS | Saved new best reduction to ");
341 }
342 // Delete uninteresting chunks
343 erase_if(ChunksStillConsideredInteresting,
344 [&UninterestingChunks](const Chunk &C) {
345 return UninterestingChunks.count(C);
346 });
347 } while (!ChunksStillConsideredInteresting.empty() &&
348 (FoundAtLeastOneNewUninterestingChunkWithCurrentGranularity ||
349 increaseGranularity(ChunksStillConsideredInteresting)));
350
351 // If we reduced the testcase replace it
352 if (ReducedProgram)
353 Test.setProgram(std::move(ReducedProgram));
354 if (Verbose)
355 errs() << "Couldn't increase anymore.\n";
356 errs() << "----------------------------\n";
357 }
358