1 //===- ExtractFunction.cpp - Extract a function from Program --------------===//
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 implements several methods that are used to extract functions,
10 // loops, or portions of a module from the rest of the module.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "BugDriver.h"
15 #include "llvm/IR/Constants.h"
16 #include "llvm/IR/DataLayout.h"
17 #include "llvm/IR/DerivedTypes.h"
18 #include "llvm/IR/LLVMContext.h"
19 #include "llvm/IR/LegacyPassManager.h"
20 #include "llvm/IR/Module.h"
21 #include "llvm/IR/Verifier.h"
22 #include "llvm/Pass.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/FileUtilities.h"
26 #include "llvm/Support/Path.h"
27 #include "llvm/Support/Signals.h"
28 #include "llvm/Support/ToolOutputFile.h"
29 #include "llvm/Transforms/IPO.h"
30 #include "llvm/Transforms/Scalar.h"
31 #include "llvm/Transforms/Utils/Cloning.h"
32 #include "llvm/Transforms/Utils/CodeExtractor.h"
33 #include <set>
34 using namespace llvm;
35 
36 #define DEBUG_TYPE "bugpoint"
37 
38 namespace llvm {
39 bool DisableSimplifyCFG = false;
40 extern cl::opt<std::string> OutputPrefix;
41 } // End llvm namespace
42 
43 namespace {
44 cl::opt<bool> NoDCE("disable-dce",
45                     cl::desc("Do not use the -dce pass to reduce testcases"));
46 cl::opt<bool, true>
47     NoSCFG("disable-simplifycfg", cl::location(DisableSimplifyCFG),
48            cl::desc("Do not use the -simplifycfg pass to reduce testcases"));
49 
50 Function *globalInitUsesExternalBA(GlobalVariable *GV) {
51   if (!GV->hasInitializer())
52     return nullptr;
53 
54   Constant *I = GV->getInitializer();
55 
56   // walk the values used by the initializer
57   // (and recurse into things like ConstantExpr)
58   std::vector<Constant *> Todo;
59   std::set<Constant *> Done;
60   Todo.push_back(I);
61 
62   while (!Todo.empty()) {
63     Constant *V = Todo.back();
64     Todo.pop_back();
65     Done.insert(V);
66 
67     if (BlockAddress *BA = dyn_cast<BlockAddress>(V)) {
68       Function *F = BA->getFunction();
69       if (F->isDeclaration())
70         return F;
71     }
72 
73     for (User::op_iterator i = V->op_begin(), e = V->op_end(); i != e; ++i) {
74       Constant *C = dyn_cast<Constant>(*i);
75       if (C && !isa<GlobalValue>(C) && !Done.count(C))
76         Todo.push_back(C);
77     }
78   }
79   return nullptr;
80 }
81 } // end anonymous namespace
82 
83 std::unique_ptr<Module>
84 BugDriver::deleteInstructionFromProgram(const Instruction *I,
85                                         unsigned Simplification) {
86   // FIXME, use vmap?
87   std::unique_ptr<Module> Clone = CloneModule(*Program);
88 
89   const BasicBlock *PBB = I->getParent();
90   const Function *PF = PBB->getParent();
91 
92   Module::iterator RFI = Clone->begin(); // Get iterator to corresponding fn
93   std::advance(
94       RFI, std::distance(PF->getParent()->begin(), Module::const_iterator(PF)));
95 
96   Function::iterator RBI = RFI->begin(); // Get iterator to corresponding BB
97   std::advance(RBI, std::distance(PF->begin(), Function::const_iterator(PBB)));
98 
99   BasicBlock::iterator RI = RBI->begin(); // Get iterator to corresponding inst
100   std::advance(RI, std::distance(PBB->begin(), BasicBlock::const_iterator(I)));
101   Instruction *TheInst = &*RI; // Got the corresponding instruction!
102 
103   // If this instruction produces a value, replace any users with null values
104   if (!TheInst->getType()->isVoidTy())
105     TheInst->replaceAllUsesWith(Constant::getNullValue(TheInst->getType()));
106 
107   // Remove the instruction from the program.
108   TheInst->eraseFromParent();
109 
110   // Spiff up the output a little bit.
111   std::vector<std::string> Passes;
112 
113   /// Can we get rid of the -disable-* options?
114   if (Simplification > 1 && !NoDCE)
115     Passes.push_back("dce");
116   if (Simplification && !DisableSimplifyCFG)
117     Passes.push_back("simplifycfg"); // Delete dead control flow
118 
119   Passes.push_back("verify");
120   std::unique_ptr<Module> New = runPassesOn(Clone.get(), Passes);
121   if (!New) {
122     errs() << "Instruction removal failed.  Sorry. :(  Please report a bug!\n";
123     exit(1);
124   }
125   return New;
126 }
127 
128 std::unique_ptr<Module>
129 BugDriver::performFinalCleanups(std::unique_ptr<Module> M,
130                                 bool MayModifySemantics) {
131   // Make all functions external, so GlobalDCE doesn't delete them...
132   for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
133     I->setLinkage(GlobalValue::ExternalLinkage);
134 
135   std::vector<std::string> CleanupPasses;
136 
137   if (MayModifySemantics)
138     CleanupPasses.push_back("deadarghaX0r");
139   else
140     CleanupPasses.push_back("deadargelim");
141 
142   std::unique_ptr<Module> New = runPassesOn(M.get(), CleanupPasses);
143   if (!New) {
144     errs() << "Final cleanups failed.  Sorry. :(  Please report a bug!\n";
145     return nullptr;
146   }
147   return New;
148 }
149 
150 std::unique_ptr<Module> BugDriver::extractLoop(Module *M) {
151   std::vector<std::string> LoopExtractPasses;
152   LoopExtractPasses.push_back("loop-extract-single");
153 
154   std::unique_ptr<Module> NewM = runPassesOn(M, LoopExtractPasses);
155   if (!NewM) {
156     outs() << "*** Loop extraction failed: ";
157     EmitProgressBitcode(*M, "loopextraction", true);
158     outs() << "*** Sorry. :(  Please report a bug!\n";
159     return nullptr;
160   }
161 
162   // Check to see if we created any new functions.  If not, no loops were
163   // extracted and we should return null.  Limit the number of loops we extract
164   // to avoid taking forever.
165   static unsigned NumExtracted = 32;
166   if (M->size() == NewM->size() || --NumExtracted == 0) {
167     return nullptr;
168   } else {
169     assert(M->size() < NewM->size() && "Loop extract removed functions?");
170     Module::iterator MI = NewM->begin();
171     for (unsigned i = 0, e = M->size(); i != e; ++i)
172       ++MI;
173   }
174 
175   return NewM;
176 }
177 
178 static void eliminateAliases(GlobalValue *GV) {
179   // First, check whether a GlobalAlias references this definition.
180   // GlobalAlias MAY NOT reference declarations.
181   for (;;) {
182     // 1. Find aliases
183     SmallVector<GlobalAlias *, 1> aliases;
184     Module *M = GV->getParent();
185     for (Module::alias_iterator I = M->alias_begin(), E = M->alias_end();
186          I != E; ++I)
187       if (I->getAliasee()->stripPointerCasts() == GV)
188         aliases.push_back(&*I);
189     if (aliases.empty())
190       break;
191     // 2. Resolve aliases
192     for (unsigned i = 0, e = aliases.size(); i < e; ++i) {
193       aliases[i]->replaceAllUsesWith(aliases[i]->getAliasee());
194       aliases[i]->eraseFromParent();
195     }
196     // 3. Repeat until no more aliases found; there might
197     // be an alias to an alias...
198   }
199 }
200 
201 //
202 // DeleteGlobalInitializer - "Remove" the global variable by deleting its
203 // initializer,
204 // making it external.
205 //
206 void llvm::DeleteGlobalInitializer(GlobalVariable *GV) {
207   eliminateAliases(GV);
208   GV->setInitializer(nullptr);
209   GV->setComdat(nullptr);
210 }
211 
212 // DeleteFunctionBody - "Remove" the function by deleting all of its basic
213 // blocks, making it external.
214 //
215 void llvm::DeleteFunctionBody(Function *F) {
216   eliminateAliases(F);
217   // Function declarations can't have comdats.
218   F->setComdat(nullptr);
219 
220   // delete the body of the function...
221   F->deleteBody();
222   assert(F->isDeclaration() && "This didn't make the function external!");
223 }
224 
225 /// GetTorInit - Given a list of entries for static ctors/dtors, return them
226 /// as a constant array.
227 static Constant *GetTorInit(std::vector<std::pair<Function *, int>> &TorList) {
228   assert(!TorList.empty() && "Don't create empty tor list!");
229   std::vector<Constant *> ArrayElts;
230   Type *Int32Ty = Type::getInt32Ty(TorList[0].first->getContext());
231 
232   StructType *STy = StructType::get(Int32Ty, TorList[0].first->getType());
233   for (unsigned i = 0, e = TorList.size(); i != e; ++i) {
234     Constant *Elts[] = {ConstantInt::get(Int32Ty, TorList[i].second),
235                         TorList[i].first};
236     ArrayElts.push_back(ConstantStruct::get(STy, Elts));
237   }
238   return ConstantArray::get(
239       ArrayType::get(ArrayElts[0]->getType(), ArrayElts.size()), ArrayElts);
240 }
241 
242 /// SplitStaticCtorDtor - A module was recently split into two parts, M1/M2, and
243 /// M1 has all of the global variables.  If M2 contains any functions that are
244 /// static ctors/dtors, we need to add an llvm.global_[cd]tors global to M2, and
245 /// prune appropriate entries out of M1s list.
246 static void SplitStaticCtorDtor(const char *GlobalName, Module *M1, Module *M2,
247                                 ValueToValueMapTy &VMap) {
248   GlobalVariable *GV = M1->getNamedGlobal(GlobalName);
249   if (!GV || GV->isDeclaration() || GV->hasLocalLinkage() || !GV->use_empty())
250     return;
251 
252   std::vector<std::pair<Function *, int>> M1Tors, M2Tors;
253   ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer());
254   if (!InitList)
255     return;
256 
257   for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i) {
258     if (ConstantStruct *CS =
259             dyn_cast<ConstantStruct>(InitList->getOperand(i))) {
260       if (CS->getNumOperands() != 2)
261         return; // Not array of 2-element structs.
262 
263       if (CS->getOperand(1)->isNullValue())
264         break; // Found a null terminator, stop here.
265 
266       ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0));
267       int Priority = CI ? CI->getSExtValue() : 0;
268 
269       Constant *FP = CS->getOperand(1);
270       if (ConstantExpr *CE = dyn_cast<ConstantExpr>(FP))
271         if (CE->isCast())
272           FP = CE->getOperand(0);
273       if (Function *F = dyn_cast<Function>(FP)) {
274         if (!F->isDeclaration())
275           M1Tors.push_back(std::make_pair(F, Priority));
276         else {
277           // Map to M2's version of the function.
278           F = cast<Function>(VMap[F]);
279           M2Tors.push_back(std::make_pair(F, Priority));
280         }
281       }
282     }
283   }
284 
285   GV->eraseFromParent();
286   if (!M1Tors.empty()) {
287     Constant *M1Init = GetTorInit(M1Tors);
288     new GlobalVariable(*M1, M1Init->getType(), false,
289                        GlobalValue::AppendingLinkage, M1Init, GlobalName);
290   }
291 
292   GV = M2->getNamedGlobal(GlobalName);
293   assert(GV && "Not a clone of M1?");
294   assert(GV->use_empty() && "llvm.ctors shouldn't have uses!");
295 
296   GV->eraseFromParent();
297   if (!M2Tors.empty()) {
298     Constant *M2Init = GetTorInit(M2Tors);
299     new GlobalVariable(*M2, M2Init->getType(), false,
300                        GlobalValue::AppendingLinkage, M2Init, GlobalName);
301   }
302 }
303 
304 std::unique_ptr<Module>
305 llvm::SplitFunctionsOutOfModule(Module *M, const std::vector<Function *> &F,
306                                 ValueToValueMapTy &VMap) {
307   // Make sure functions & globals are all external so that linkage
308   // between the two modules will work.
309   for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
310     I->setLinkage(GlobalValue::ExternalLinkage);
311   for (Module::global_iterator I = M->global_begin(), E = M->global_end();
312        I != E; ++I) {
313     if (I->hasName() && I->getName()[0] == '\01')
314       I->setName(I->getName().substr(1));
315     I->setLinkage(GlobalValue::ExternalLinkage);
316   }
317 
318   ValueToValueMapTy NewVMap;
319   std::unique_ptr<Module> New = CloneModule(*M, NewVMap);
320 
321   // Remove the Test functions from the Safe module
322   std::set<Function *> TestFunctions;
323   for (unsigned i = 0, e = F.size(); i != e; ++i) {
324     Function *TNOF = cast<Function>(VMap[F[i]]);
325     LLVM_DEBUG(errs() << "Removing function ");
326     LLVM_DEBUG(TNOF->printAsOperand(errs(), false));
327     LLVM_DEBUG(errs() << "\n");
328     TestFunctions.insert(cast<Function>(NewVMap[TNOF]));
329     DeleteFunctionBody(TNOF); // Function is now external in this module!
330   }
331 
332   // Remove the Safe functions from the Test module
333   for (Function &I : *New)
334     if (!TestFunctions.count(&I))
335       DeleteFunctionBody(&I);
336 
337   // Try to split the global initializers evenly
338   for (GlobalVariable &I : M->globals()) {
339     GlobalVariable *GV = cast<GlobalVariable>(NewVMap[&I]);
340     if (Function *TestFn = globalInitUsesExternalBA(&I)) {
341       if (Function *SafeFn = globalInitUsesExternalBA(GV)) {
342         errs() << "*** Error: when reducing functions, encountered "
343                   "the global '";
344         GV->printAsOperand(errs(), false);
345         errs() << "' with an initializer that references blockaddresses "
346                   "from safe function '"
347                << SafeFn->getName() << "' and from test function '"
348                << TestFn->getName() << "'.\n";
349         exit(1);
350       }
351       DeleteGlobalInitializer(&I); // Delete the initializer to make it external
352     } else {
353       // If we keep it in the safe module, then delete it in the test module
354       DeleteGlobalInitializer(GV);
355     }
356   }
357 
358   // Make sure that there is a global ctor/dtor array in both halves of the
359   // module if they both have static ctor/dtor functions.
360   SplitStaticCtorDtor("llvm.global_ctors", M, New.get(), NewVMap);
361   SplitStaticCtorDtor("llvm.global_dtors", M, New.get(), NewVMap);
362 
363   return New;
364 }
365 
366 //===----------------------------------------------------------------------===//
367 // Basic Block Extraction Code
368 //===----------------------------------------------------------------------===//
369 
370 std::unique_ptr<Module>
371 BugDriver::extractMappedBlocksFromModule(const std::vector<BasicBlock *> &BBs,
372                                          Module *M) {
373   auto Temp = sys::fs::TempFile::create(OutputPrefix + "-extractblocks%%%%%%%");
374   if (!Temp) {
375     outs() << "*** Basic Block extraction failed!\n";
376     errs() << "Error creating temporary file: " << toString(Temp.takeError())
377            << "\n";
378     EmitProgressBitcode(*M, "basicblockextractfail", true);
379     return nullptr;
380   }
381   DiscardTemp Discard{*Temp};
382 
383   // Extract all of the blocks except the ones in BBs.
384   SmallVector<BasicBlock *, 32> BlocksToExtract;
385   for (Function &F : *M)
386     for (BasicBlock &BB : F)
387       // Check if this block is going to be extracted.
388       if (!llvm::is_contained(BBs, &BB))
389         BlocksToExtract.push_back(&BB);
390 
391   raw_fd_ostream OS(Temp->FD, /*shouldClose*/ false);
392   for (BasicBlock *BB : BBs) {
393     // If the BB doesn't have a name, give it one so we have something to key
394     // off of.
395     if (!BB->hasName())
396       BB->setName("tmpbb");
397     OS << BB->getParent()->getName() << " " << BB->getName() << "\n";
398   }
399   OS.flush();
400   if (OS.has_error()) {
401     errs() << "Error writing list of blocks to not extract\n";
402     EmitProgressBitcode(*M, "basicblockextractfail", true);
403     OS.clear_error();
404     return nullptr;
405   }
406 
407   std::string uniqueFN = "--extract-blocks-file=";
408   uniqueFN += Temp->TmpName;
409 
410   std::vector<std::string> PI;
411   PI.push_back("extract-blocks");
412   std::unique_ptr<Module> Ret = runPassesOn(M, PI, {uniqueFN});
413 
414   if (!Ret) {
415     outs() << "*** Basic Block extraction failed, please report a bug!\n";
416     EmitProgressBitcode(*M, "basicblockextractfail", true);
417   }
418   return Ret;
419 }
420