1 //===-- ThreadSanitizer.cpp - race detector -------------------------------===//
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 is a part of ThreadSanitizer, a race detector.
11 //
12 // The tool is under development, for the details about previous versions see
13 // http://code.google.com/p/data-race-test
14 //
15 // The instrumentation phase is quite simple:
16 //   - Insert calls to run-time library before every memory access.
17 //      - Optimizations may apply to avoid instrumenting some of the accesses.
18 //   - Insert calls at function entry/exit.
19 // The rest is handled by the run-time library.
20 //===----------------------------------------------------------------------===//
21 
22 #define DEBUG_TYPE "tsan"
23 
24 #include "BlackList.h"
25 #include "llvm/Function.h"
26 #include "llvm/IRBuilder.h"
27 #include "llvm/Intrinsics.h"
28 #include "llvm/LLVMContext.h"
29 #include "llvm/Metadata.h"
30 #include "llvm/Module.h"
31 #include "llvm/Type.h"
32 #include "llvm/ADT/SmallSet.h"
33 #include "llvm/ADT/SmallString.h"
34 #include "llvm/ADT/SmallVector.h"
35 #include "llvm/ADT/Statistic.h"
36 #include "llvm/ADT/StringExtras.h"
37 #include "llvm/Support/CommandLine.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/MathExtras.h"
40 #include "llvm/Support/raw_ostream.h"
41 #include "llvm/DataLayout.h"
42 #include "llvm/Transforms/Instrumentation.h"
43 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
44 #include "llvm/Transforms/Utils/ModuleUtils.h"
45 
46 using namespace llvm;
47 
48 static cl::opt<std::string>  ClBlackListFile("tsan-blacklist",
49        cl::desc("Blacklist file"), cl::Hidden);
50 static cl::opt<bool>  ClInstrumentMemoryAccesses(
51     "tsan-instrument-memory-accesses", cl::init(true),
52     cl::desc("Instrument memory accesses"), cl::Hidden);
53 static cl::opt<bool>  ClInstrumentFuncEntryExit(
54     "tsan-instrument-func-entry-exit", cl::init(true),
55     cl::desc("Instrument function entry and exit"), cl::Hidden);
56 static cl::opt<bool>  ClInstrumentAtomics(
57     "tsan-instrument-atomics", cl::init(true),
58     cl::desc("Instrument atomics"), cl::Hidden);
59 
60 STATISTIC(NumInstrumentedReads, "Number of instrumented reads");
61 STATISTIC(NumInstrumentedWrites, "Number of instrumented writes");
62 STATISTIC(NumOmittedReadsBeforeWrite,
63           "Number of reads ignored due to following writes");
64 STATISTIC(NumAccessesWithBadSize, "Number of accesses with bad size");
65 STATISTIC(NumInstrumentedVtableWrites, "Number of vtable ptr writes");
66 STATISTIC(NumOmittedReadsFromConstantGlobals,
67           "Number of reads from constant globals");
68 STATISTIC(NumOmittedReadsFromVtable, "Number of vtable reads");
69 
70 namespace {
71 
72 /// ThreadSanitizer: instrument the code in module to find races.
73 struct ThreadSanitizer : public FunctionPass {
74   ThreadSanitizer();
75   const char *getPassName() const;
76   bool runOnFunction(Function &F);
77   bool doInitialization(Module &M);
78   static char ID;  // Pass identification, replacement for typeid.
79 
80  private:
81   bool instrumentLoadOrStore(Instruction *I);
82   bool instrumentAtomic(Instruction *I);
83   void chooseInstructionsToInstrument(SmallVectorImpl<Instruction*> &Local,
84                                       SmallVectorImpl<Instruction*> &All);
85   bool addrPointsToConstantData(Value *Addr);
86   int getMemoryAccessFuncIndex(Value *Addr);
87 
88   DataLayout *TD;
89   OwningPtr<BlackList> BL;
90   IntegerType *OrdTy;
91   // Callbacks to run-time library are computed in doInitialization.
92   Function *TsanFuncEntry;
93   Function *TsanFuncExit;
94   // Accesses sizes are powers of two: 1, 2, 4, 8, 16.
95   static const size_t kNumberOfAccessSizes = 5;
96   Function *TsanRead[kNumberOfAccessSizes];
97   Function *TsanWrite[kNumberOfAccessSizes];
98   Function *TsanAtomicLoad[kNumberOfAccessSizes];
99   Function *TsanAtomicStore[kNumberOfAccessSizes];
100   Function *TsanAtomicRMW[AtomicRMWInst::LAST_BINOP + 1][kNumberOfAccessSizes];
101   Function *TsanAtomicCAS[kNumberOfAccessSizes];
102   Function *TsanAtomicThreadFence;
103   Function *TsanAtomicSignalFence;
104   Function *TsanVptrUpdate;
105 };
106 }  // namespace
107 
108 char ThreadSanitizer::ID = 0;
109 INITIALIZE_PASS(ThreadSanitizer, "tsan",
110     "ThreadSanitizer: detects data races.",
111     false, false)
112 
113 const char *ThreadSanitizer::getPassName() const {
114   return "ThreadSanitizer";
115 }
116 
117 ThreadSanitizer::ThreadSanitizer()
118   : FunctionPass(ID),
119   TD(NULL) {
120 }
121 
122 FunctionPass *llvm::createThreadSanitizerPass() {
123   return new ThreadSanitizer();
124 }
125 
126 static Function *checkInterfaceFunction(Constant *FuncOrBitcast) {
127   if (Function *F = dyn_cast<Function>(FuncOrBitcast))
128      return F;
129   FuncOrBitcast->dump();
130   report_fatal_error("ThreadSanitizer interface function redefined");
131 }
132 
133 bool ThreadSanitizer::doInitialization(Module &M) {
134   TD = getAnalysisIfAvailable<DataLayout>();
135   if (!TD)
136     return false;
137   BL.reset(new BlackList(ClBlackListFile));
138 
139   // Always insert a call to __tsan_init into the module's CTORs.
140   IRBuilder<> IRB(M.getContext());
141   Value *TsanInit = M.getOrInsertFunction("__tsan_init",
142                                           IRB.getVoidTy(), NULL);
143   appendToGlobalCtors(M, cast<Function>(TsanInit), 0);
144 
145   // Initialize the callbacks.
146   TsanFuncEntry = checkInterfaceFunction(M.getOrInsertFunction(
147       "__tsan_func_entry", IRB.getVoidTy(), IRB.getInt8PtrTy(), NULL));
148   TsanFuncExit = checkInterfaceFunction(M.getOrInsertFunction(
149       "__tsan_func_exit", IRB.getVoidTy(), NULL));
150   OrdTy = IRB.getInt32Ty();
151   for (size_t i = 0; i < kNumberOfAccessSizes; ++i) {
152     const size_t ByteSize = 1 << i;
153     const size_t BitSize = ByteSize * 8;
154     SmallString<32> ReadName("__tsan_read" + itostr(ByteSize));
155     TsanRead[i] = checkInterfaceFunction(M.getOrInsertFunction(
156         ReadName, IRB.getVoidTy(), IRB.getInt8PtrTy(), NULL));
157 
158     SmallString<32> WriteName("__tsan_write" + itostr(ByteSize));
159     TsanWrite[i] = checkInterfaceFunction(M.getOrInsertFunction(
160         WriteName, IRB.getVoidTy(), IRB.getInt8PtrTy(), NULL));
161 
162     Type *Ty = Type::getIntNTy(M.getContext(), BitSize);
163     Type *PtrTy = Ty->getPointerTo();
164     SmallString<32> AtomicLoadName("__tsan_atomic" + itostr(BitSize) +
165                                    "_load");
166     TsanAtomicLoad[i] = checkInterfaceFunction(M.getOrInsertFunction(
167         AtomicLoadName, Ty, PtrTy, OrdTy, NULL));
168 
169     SmallString<32> AtomicStoreName("__tsan_atomic" + itostr(BitSize) +
170                                     "_store");
171     TsanAtomicStore[i] = checkInterfaceFunction(M.getOrInsertFunction(
172         AtomicStoreName, IRB.getVoidTy(), PtrTy, Ty, OrdTy,
173         NULL));
174 
175     for (int op = AtomicRMWInst::FIRST_BINOP;
176         op <= AtomicRMWInst::LAST_BINOP; ++op) {
177       TsanAtomicRMW[op][i] = NULL;
178       const char *NamePart = NULL;
179       if (op == AtomicRMWInst::Xchg)
180         NamePart = "_exchange";
181       else if (op == AtomicRMWInst::Add)
182         NamePart = "_fetch_add";
183       else if (op == AtomicRMWInst::Sub)
184         NamePart = "_fetch_sub";
185       else if (op == AtomicRMWInst::And)
186         NamePart = "_fetch_and";
187       else if (op == AtomicRMWInst::Or)
188         NamePart = "_fetch_or";
189       else if (op == AtomicRMWInst::Xor)
190         NamePart = "_fetch_xor";
191       else if (op == AtomicRMWInst::Nand)
192         NamePart = "_fetch_nand";
193       else
194         continue;
195       SmallString<32> RMWName("__tsan_atomic" + itostr(BitSize) + NamePart);
196       TsanAtomicRMW[op][i] = checkInterfaceFunction(M.getOrInsertFunction(
197           RMWName, Ty, PtrTy, Ty, OrdTy, NULL));
198     }
199 
200     SmallString<32> AtomicCASName("__tsan_atomic" + itostr(BitSize) +
201                                   "_compare_exchange_val");
202     TsanAtomicCAS[i] = checkInterfaceFunction(M.getOrInsertFunction(
203         AtomicCASName, Ty, PtrTy, Ty, Ty, OrdTy, OrdTy, NULL));
204   }
205   TsanVptrUpdate = checkInterfaceFunction(M.getOrInsertFunction(
206       "__tsan_vptr_update", IRB.getVoidTy(), IRB.getInt8PtrTy(),
207       IRB.getInt8PtrTy(), NULL));
208   TsanAtomicThreadFence = checkInterfaceFunction(M.getOrInsertFunction(
209       "__tsan_atomic_thread_fence", IRB.getVoidTy(), OrdTy, NULL));
210   TsanAtomicSignalFence = checkInterfaceFunction(M.getOrInsertFunction(
211       "__tsan_atomic_signal_fence", IRB.getVoidTy(), OrdTy, NULL));
212   return true;
213 }
214 
215 static bool isVtableAccess(Instruction *I) {
216   if (MDNode *Tag = I->getMetadata(LLVMContext::MD_tbaa)) {
217     if (Tag->getNumOperands() < 1) return false;
218     if (MDString *Tag1 = dyn_cast<MDString>(Tag->getOperand(0))) {
219       if (Tag1->getString() == "vtable pointer") return true;
220     }
221   }
222   return false;
223 }
224 
225 bool ThreadSanitizer::addrPointsToConstantData(Value *Addr) {
226   // If this is a GEP, just analyze its pointer operand.
227   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Addr))
228     Addr = GEP->getPointerOperand();
229 
230   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
231     if (GV->isConstant()) {
232       // Reads from constant globals can not race with any writes.
233       NumOmittedReadsFromConstantGlobals++;
234       return true;
235     }
236   } else if (LoadInst *L = dyn_cast<LoadInst>(Addr)) {
237     if (isVtableAccess(L)) {
238       // Reads from a vtable pointer can not race with any writes.
239       NumOmittedReadsFromVtable++;
240       return true;
241     }
242   }
243   return false;
244 }
245 
246 // Instrumenting some of the accesses may be proven redundant.
247 // Currently handled:
248 //  - read-before-write (within same BB, no calls between)
249 //
250 // We do not handle some of the patterns that should not survive
251 // after the classic compiler optimizations.
252 // E.g. two reads from the same temp should be eliminated by CSE,
253 // two writes should be eliminated by DSE, etc.
254 //
255 // 'Local' is a vector of insns within the same BB (no calls between).
256 // 'All' is a vector of insns that will be instrumented.
257 void ThreadSanitizer::chooseInstructionsToInstrument(
258     SmallVectorImpl<Instruction*> &Local,
259     SmallVectorImpl<Instruction*> &All) {
260   SmallSet<Value*, 8> WriteTargets;
261   // Iterate from the end.
262   for (SmallVectorImpl<Instruction*>::reverse_iterator It = Local.rbegin(),
263        E = Local.rend(); It != E; ++It) {
264     Instruction *I = *It;
265     if (StoreInst *Store = dyn_cast<StoreInst>(I)) {
266       WriteTargets.insert(Store->getPointerOperand());
267     } else {
268       LoadInst *Load = cast<LoadInst>(I);
269       Value *Addr = Load->getPointerOperand();
270       if (WriteTargets.count(Addr)) {
271         // We will write to this temp, so no reason to analyze the read.
272         NumOmittedReadsBeforeWrite++;
273         continue;
274       }
275       if (addrPointsToConstantData(Addr)) {
276         // Addr points to some constant data -- it can not race with any writes.
277         continue;
278       }
279     }
280     All.push_back(I);
281   }
282   Local.clear();
283 }
284 
285 static bool isAtomic(Instruction *I) {
286   if (LoadInst *LI = dyn_cast<LoadInst>(I))
287     return LI->isAtomic() && LI->getSynchScope() == CrossThread;
288   if (StoreInst *SI = dyn_cast<StoreInst>(I))
289     return SI->isAtomic() && SI->getSynchScope() == CrossThread;
290   if (isa<AtomicRMWInst>(I))
291     return true;
292   if (isa<AtomicCmpXchgInst>(I))
293     return true;
294   if (isa<FenceInst>(I))
295     return true;
296   return false;
297 }
298 
299 bool ThreadSanitizer::runOnFunction(Function &F) {
300   if (!TD) return false;
301   if (BL->isIn(F)) return false;
302   SmallVector<Instruction*, 8> RetVec;
303   SmallVector<Instruction*, 8> AllLoadsAndStores;
304   SmallVector<Instruction*, 8> LocalLoadsAndStores;
305   SmallVector<Instruction*, 8> AtomicAccesses;
306   bool Res = false;
307   bool HasCalls = false;
308 
309   // Traverse all instructions, collect loads/stores/returns, check for calls.
310   for (Function::iterator FI = F.begin(), FE = F.end();
311        FI != FE; ++FI) {
312     BasicBlock &BB = *FI;
313     for (BasicBlock::iterator BI = BB.begin(), BE = BB.end();
314          BI != BE; ++BI) {
315       if (isAtomic(BI))
316         AtomicAccesses.push_back(BI);
317       else if (isa<LoadInst>(BI) || isa<StoreInst>(BI))
318         LocalLoadsAndStores.push_back(BI);
319       else if (isa<ReturnInst>(BI))
320         RetVec.push_back(BI);
321       else if (isa<CallInst>(BI) || isa<InvokeInst>(BI)) {
322         HasCalls = true;
323         chooseInstructionsToInstrument(LocalLoadsAndStores, AllLoadsAndStores);
324       }
325     }
326     chooseInstructionsToInstrument(LocalLoadsAndStores, AllLoadsAndStores);
327   }
328 
329   // We have collected all loads and stores.
330   // FIXME: many of these accesses do not need to be checked for races
331   // (e.g. variables that do not escape, etc).
332 
333   // Instrument memory accesses.
334   if (ClInstrumentMemoryAccesses)
335     for (size_t i = 0, n = AllLoadsAndStores.size(); i < n; ++i) {
336       Res |= instrumentLoadOrStore(AllLoadsAndStores[i]);
337     }
338 
339   // Instrument atomic memory accesses.
340   if (ClInstrumentAtomics)
341     for (size_t i = 0, n = AtomicAccesses.size(); i < n; ++i) {
342       Res |= instrumentAtomic(AtomicAccesses[i]);
343     }
344 
345   // Instrument function entry/exit points if there were instrumented accesses.
346   if ((Res || HasCalls) && ClInstrumentFuncEntryExit) {
347     IRBuilder<> IRB(F.getEntryBlock().getFirstNonPHI());
348     Value *ReturnAddress = IRB.CreateCall(
349         Intrinsic::getDeclaration(F.getParent(), Intrinsic::returnaddress),
350         IRB.getInt32(0));
351     IRB.CreateCall(TsanFuncEntry, ReturnAddress);
352     for (size_t i = 0, n = RetVec.size(); i < n; ++i) {
353       IRBuilder<> IRBRet(RetVec[i]);
354       IRBRet.CreateCall(TsanFuncExit);
355     }
356     Res = true;
357   }
358   return Res;
359 }
360 
361 bool ThreadSanitizer::instrumentLoadOrStore(Instruction *I) {
362   IRBuilder<> IRB(I);
363   bool IsWrite = isa<StoreInst>(*I);
364   Value *Addr = IsWrite
365       ? cast<StoreInst>(I)->getPointerOperand()
366       : cast<LoadInst>(I)->getPointerOperand();
367   int Idx = getMemoryAccessFuncIndex(Addr);
368   if (Idx < 0)
369     return false;
370   if (IsWrite && isVtableAccess(I)) {
371     DEBUG(dbgs() << "  VPTR : " << *I << "\n");
372     Value *StoredValue = cast<StoreInst>(I)->getValueOperand();
373     // StoredValue does not necessary have a pointer type.
374     if (isa<IntegerType>(StoredValue->getType()))
375       StoredValue = IRB.CreateIntToPtr(StoredValue, IRB.getInt8PtrTy());
376     // Call TsanVptrUpdate.
377     IRB.CreateCall2(TsanVptrUpdate,
378                     IRB.CreatePointerCast(Addr, IRB.getInt8PtrTy()),
379                     IRB.CreatePointerCast(StoredValue, IRB.getInt8PtrTy()));
380     NumInstrumentedVtableWrites++;
381     return true;
382   }
383   Value *OnAccessFunc = IsWrite ? TsanWrite[Idx] : TsanRead[Idx];
384   IRB.CreateCall(OnAccessFunc, IRB.CreatePointerCast(Addr, IRB.getInt8PtrTy()));
385   if (IsWrite) NumInstrumentedWrites++;
386   else         NumInstrumentedReads++;
387   return true;
388 }
389 
390 static ConstantInt *createOrdering(IRBuilder<> *IRB, AtomicOrdering ord) {
391   uint32_t v = 0;
392   switch (ord) {
393     case NotAtomic:              assert(false);
394     case Unordered:              // Fall-through.
395     case Monotonic:              v = 0; break;
396     // case Consume:                v = 1; break;  // Not specified yet.
397     case Acquire:                v = 2; break;
398     case Release:                v = 3; break;
399     case AcquireRelease:         v = 4; break;
400     case SequentiallyConsistent: v = 5; break;
401   }
402   return IRB->getInt32(v);
403 }
404 
405 static ConstantInt *createFailOrdering(IRBuilder<> *IRB, AtomicOrdering ord) {
406   uint32_t v = 0;
407   switch (ord) {
408     case NotAtomic:              assert(false);
409     case Unordered:              // Fall-through.
410     case Monotonic:              v = 0; break;
411     // case Consume:                v = 1; break;  // Not specified yet.
412     case Acquire:                v = 2; break;
413     case Release:                v = 0; break;
414     case AcquireRelease:         v = 2; break;
415     case SequentiallyConsistent: v = 5; break;
416   }
417   return IRB->getInt32(v);
418 }
419 
420 // Both llvm and ThreadSanitizer atomic operations are based on C++11/C1x
421 // standards.  For background see C++11 standard.  A slightly older, publically
422 // available draft of the standard (not entirely up-to-date, but close enough
423 // for casual browsing) is available here:
424 // http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf
425 // The following page contains more background information:
426 // http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/
427 
428 bool ThreadSanitizer::instrumentAtomic(Instruction *I) {
429   IRBuilder<> IRB(I);
430   if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
431     Value *Addr = LI->getPointerOperand();
432     int Idx = getMemoryAccessFuncIndex(Addr);
433     if (Idx < 0)
434       return false;
435     const size_t ByteSize = 1 << Idx;
436     const size_t BitSize = ByteSize * 8;
437     Type *Ty = Type::getIntNTy(IRB.getContext(), BitSize);
438     Type *PtrTy = Ty->getPointerTo();
439     Value *Args[] = {IRB.CreatePointerCast(Addr, PtrTy),
440                      createOrdering(&IRB, LI->getOrdering())};
441     CallInst *C = CallInst::Create(TsanAtomicLoad[Idx],
442                                    ArrayRef<Value*>(Args));
443     ReplaceInstWithInst(I, C);
444 
445   } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
446     Value *Addr = SI->getPointerOperand();
447     int Idx = getMemoryAccessFuncIndex(Addr);
448     if (Idx < 0)
449       return false;
450     const size_t ByteSize = 1 << Idx;
451     const size_t BitSize = ByteSize * 8;
452     Type *Ty = Type::getIntNTy(IRB.getContext(), BitSize);
453     Type *PtrTy = Ty->getPointerTo();
454     Value *Args[] = {IRB.CreatePointerCast(Addr, PtrTy),
455                      IRB.CreateIntCast(SI->getValueOperand(), Ty, false),
456                      createOrdering(&IRB, SI->getOrdering())};
457     CallInst *C = CallInst::Create(TsanAtomicStore[Idx],
458                                    ArrayRef<Value*>(Args));
459     ReplaceInstWithInst(I, C);
460   } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(I)) {
461     Value *Addr = RMWI->getPointerOperand();
462     int Idx = getMemoryAccessFuncIndex(Addr);
463     if (Idx < 0)
464       return false;
465     Function *F = TsanAtomicRMW[RMWI->getOperation()][Idx];
466     if (F == NULL)
467       return false;
468     const size_t ByteSize = 1 << Idx;
469     const size_t BitSize = ByteSize * 8;
470     Type *Ty = Type::getIntNTy(IRB.getContext(), BitSize);
471     Type *PtrTy = Ty->getPointerTo();
472     Value *Args[] = {IRB.CreatePointerCast(Addr, PtrTy),
473                      IRB.CreateIntCast(RMWI->getValOperand(), Ty, false),
474                      createOrdering(&IRB, RMWI->getOrdering())};
475     CallInst *C = CallInst::Create(F, ArrayRef<Value*>(Args));
476     ReplaceInstWithInst(I, C);
477   } else if (AtomicCmpXchgInst *CASI = dyn_cast<AtomicCmpXchgInst>(I)) {
478     Value *Addr = CASI->getPointerOperand();
479     int Idx = getMemoryAccessFuncIndex(Addr);
480     if (Idx < 0)
481       return false;
482     const size_t ByteSize = 1 << Idx;
483     const size_t BitSize = ByteSize * 8;
484     Type *Ty = Type::getIntNTy(IRB.getContext(), BitSize);
485     Type *PtrTy = Ty->getPointerTo();
486     Value *Args[] = {IRB.CreatePointerCast(Addr, PtrTy),
487                      IRB.CreateIntCast(CASI->getCompareOperand(), Ty, false),
488                      IRB.CreateIntCast(CASI->getNewValOperand(), Ty, false),
489                      createOrdering(&IRB, CASI->getOrdering()),
490                      createFailOrdering(&IRB, CASI->getOrdering())};
491     CallInst *C = CallInst::Create(TsanAtomicCAS[Idx], ArrayRef<Value*>(Args));
492     ReplaceInstWithInst(I, C);
493   } else if (FenceInst *FI = dyn_cast<FenceInst>(I)) {
494     Value *Args[] = {createOrdering(&IRB, FI->getOrdering())};
495     Function *F = FI->getSynchScope() == SingleThread ?
496         TsanAtomicSignalFence : TsanAtomicThreadFence;
497     CallInst *C = CallInst::Create(F, ArrayRef<Value*>(Args));
498     ReplaceInstWithInst(I, C);
499   }
500   return true;
501 }
502 
503 int ThreadSanitizer::getMemoryAccessFuncIndex(Value *Addr) {
504   Type *OrigPtrTy = Addr->getType();
505   Type *OrigTy = cast<PointerType>(OrigPtrTy)->getElementType();
506   assert(OrigTy->isSized());
507   uint32_t TypeSize = TD->getTypeStoreSizeInBits(OrigTy);
508   if (TypeSize != 8  && TypeSize != 16 &&
509       TypeSize != 32 && TypeSize != 64 && TypeSize != 128) {
510     NumAccessesWithBadSize++;
511     // Ignore all unusual sizes.
512     return -1;
513   }
514   size_t Idx = CountTrailingZeros_32(TypeSize / 8);
515   assert(Idx < kNumberOfAccessSizes);
516   return Idx;
517 }
518