1 //===- MemProfiler.cpp - memory allocation and access profiler ------------===//
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 is a part of MemProfiler. Memory accesses are instrumented
10 // to increment the access count held in a shadow memory location, or
11 // alternatively to call into the runtime. Memory intrinsic calls (memmove,
12 // memcpy, memset) are changed to call the memory profiling runtime version
13 // instead.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "llvm/Transforms/Instrumentation/MemProfiler.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/ADT/StringRef.h"
21 #include "llvm/ADT/Triple.h"
22 #include "llvm/Analysis/ValueTracking.h"
23 #include "llvm/IR/Constant.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/Function.h"
26 #include "llvm/IR/GlobalValue.h"
27 #include "llvm/IR/IRBuilder.h"
28 #include "llvm/IR/Instruction.h"
29 #include "llvm/IR/IntrinsicInst.h"
30 #include "llvm/IR/Module.h"
31 #include "llvm/IR/Type.h"
32 #include "llvm/IR/Value.h"
33 #include "llvm/InitializePasses.h"
34 #include "llvm/Pass.h"
35 #include "llvm/ProfileData/InstrProf.h"
36 #include "llvm/Support/CommandLine.h"
37 #include "llvm/Support/Debug.h"
38 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
39 #include "llvm/Transforms/Utils/ModuleUtils.h"
40 
41 using namespace llvm;
42 
43 #define DEBUG_TYPE "memprof"
44 
45 constexpr int LLVM_MEM_PROFILER_VERSION = 1;
46 
47 // Size of memory mapped to a single shadow location.
48 constexpr uint64_t DefaultShadowGranularity = 64;
49 
50 // Scale from granularity down to shadow size.
51 constexpr uint64_t DefaultShadowScale = 3;
52 
53 constexpr char MemProfModuleCtorName[] = "memprof.module_ctor";
54 constexpr uint64_t MemProfCtorAndDtorPriority = 1;
55 // On Emscripten, the system needs more than one priorities for constructors.
56 constexpr uint64_t MemProfEmscriptenCtorAndDtorPriority = 50;
57 constexpr char MemProfInitName[] = "__memprof_init";
58 constexpr char MemProfVersionCheckNamePrefix[] =
59     "__memprof_version_mismatch_check_v";
60 
61 constexpr char MemProfShadowMemoryDynamicAddress[] =
62     "__memprof_shadow_memory_dynamic_address";
63 
64 constexpr char MemProfFilenameVar[] = "__memprof_profile_filename";
65 
66 // Command-line flags.
67 
68 static cl::opt<bool> ClInsertVersionCheck(
69     "memprof-guard-against-version-mismatch",
70     cl::desc("Guard against compiler/runtime version mismatch."), cl::Hidden,
71     cl::init(true));
72 
73 // This flag may need to be replaced with -f[no-]memprof-reads.
74 static cl::opt<bool> ClInstrumentReads("memprof-instrument-reads",
75                                        cl::desc("instrument read instructions"),
76                                        cl::Hidden, cl::init(true));
77 
78 static cl::opt<bool>
79     ClInstrumentWrites("memprof-instrument-writes",
80                        cl::desc("instrument write instructions"), cl::Hidden,
81                        cl::init(true));
82 
83 static cl::opt<bool> ClInstrumentAtomics(
84     "memprof-instrument-atomics",
85     cl::desc("instrument atomic instructions (rmw, cmpxchg)"), cl::Hidden,
86     cl::init(true));
87 
88 static cl::opt<bool> ClUseCalls(
89     "memprof-use-callbacks",
90     cl::desc("Use callbacks instead of inline instrumentation sequences."),
91     cl::Hidden, cl::init(false));
92 
93 static cl::opt<std::string>
94     ClMemoryAccessCallbackPrefix("memprof-memory-access-callback-prefix",
95                                  cl::desc("Prefix for memory access callbacks"),
96                                  cl::Hidden, cl::init("__memprof_"));
97 
98 // These flags allow to change the shadow mapping.
99 // The shadow mapping looks like
100 //    Shadow = ((Mem & mask) >> scale) + offset
101 
102 static cl::opt<int> ClMappingScale("memprof-mapping-scale",
103                                    cl::desc("scale of memprof shadow mapping"),
104                                    cl::Hidden, cl::init(DefaultShadowScale));
105 
106 static cl::opt<int>
107     ClMappingGranularity("memprof-mapping-granularity",
108                          cl::desc("granularity of memprof shadow mapping"),
109                          cl::Hidden, cl::init(DefaultShadowGranularity));
110 
111 static cl::opt<bool> ClStack("memprof-instrument-stack",
112                              cl::desc("Instrument scalar stack variables"),
113                              cl::Hidden, cl::init(false));
114 
115 // Debug flags.
116 
117 static cl::opt<int> ClDebug("memprof-debug", cl::desc("debug"), cl::Hidden,
118                             cl::init(0));
119 
120 static cl::opt<std::string> ClDebugFunc("memprof-debug-func", cl::Hidden,
121                                         cl::desc("Debug func"));
122 
123 static cl::opt<int> ClDebugMin("memprof-debug-min", cl::desc("Debug min inst"),
124                                cl::Hidden, cl::init(-1));
125 
126 static cl::opt<int> ClDebugMax("memprof-debug-max", cl::desc("Debug max inst"),
127                                cl::Hidden, cl::init(-1));
128 
129 STATISTIC(NumInstrumentedReads, "Number of instrumented reads");
130 STATISTIC(NumInstrumentedWrites, "Number of instrumented writes");
131 STATISTIC(NumSkippedStackReads, "Number of non-instrumented stack reads");
132 STATISTIC(NumSkippedStackWrites, "Number of non-instrumented stack writes");
133 
134 namespace {
135 
136 /// This struct defines the shadow mapping using the rule:
137 ///   shadow = ((mem & mask) >> Scale) ADD DynamicShadowOffset.
138 struct ShadowMapping {
139   ShadowMapping() {
140     Scale = ClMappingScale;
141     Granularity = ClMappingGranularity;
142     Mask = ~(Granularity - 1);
143   }
144 
145   int Scale;
146   int Granularity;
147   uint64_t Mask; // Computed as ~(Granularity-1)
148 };
149 
150 static uint64_t getCtorAndDtorPriority(Triple &TargetTriple) {
151   return TargetTriple.isOSEmscripten() ? MemProfEmscriptenCtorAndDtorPriority
152                                        : MemProfCtorAndDtorPriority;
153 }
154 
155 struct InterestingMemoryAccess {
156   Value *Addr = nullptr;
157   bool IsWrite;
158   Type *AccessTy;
159   uint64_t TypeSize;
160   Value *MaybeMask = nullptr;
161 };
162 
163 /// Instrument the code in module to profile memory accesses.
164 class MemProfiler {
165 public:
166   MemProfiler(Module &M) {
167     C = &(M.getContext());
168     LongSize = M.getDataLayout().getPointerSizeInBits();
169     IntptrTy = Type::getIntNTy(*C, LongSize);
170   }
171 
172   /// If it is an interesting memory access, populate information
173   /// about the access and return a InterestingMemoryAccess struct.
174   /// Otherwise return std::nullopt.
175   std::optional<InterestingMemoryAccess>
176   isInterestingMemoryAccess(Instruction *I) const;
177 
178   void instrumentMop(Instruction *I, const DataLayout &DL,
179                      InterestingMemoryAccess &Access);
180   void instrumentAddress(Instruction *OrigIns, Instruction *InsertBefore,
181                          Value *Addr, uint32_t TypeSize, bool IsWrite);
182   void instrumentMaskedLoadOrStore(const DataLayout &DL, Value *Mask,
183                                    Instruction *I, Value *Addr, Type *AccessTy,
184                                    bool IsWrite);
185   void instrumentMemIntrinsic(MemIntrinsic *MI);
186   Value *memToShadow(Value *Shadow, IRBuilder<> &IRB);
187   bool instrumentFunction(Function &F);
188   bool maybeInsertMemProfInitAtFunctionEntry(Function &F);
189   bool insertDynamicShadowAtFunctionEntry(Function &F);
190 
191 private:
192   void initializeCallbacks(Module &M);
193 
194   LLVMContext *C;
195   int LongSize;
196   Type *IntptrTy;
197   ShadowMapping Mapping;
198 
199   // These arrays is indexed by AccessIsWrite
200   FunctionCallee MemProfMemoryAccessCallback[2];
201   FunctionCallee MemProfMemoryAccessCallbackSized[2];
202 
203   FunctionCallee MemProfMemmove, MemProfMemcpy, MemProfMemset;
204   Value *DynamicShadowOffset = nullptr;
205 };
206 
207 class ModuleMemProfiler {
208 public:
209   ModuleMemProfiler(Module &M) { TargetTriple = Triple(M.getTargetTriple()); }
210 
211   bool instrumentModule(Module &);
212 
213 private:
214   Triple TargetTriple;
215   ShadowMapping Mapping;
216   Function *MemProfCtorFunction = nullptr;
217 };
218 
219 } // end anonymous namespace
220 
221 MemProfilerPass::MemProfilerPass() = default;
222 
223 PreservedAnalyses MemProfilerPass::run(Function &F,
224                                        AnalysisManager<Function> &AM) {
225   Module &M = *F.getParent();
226   MemProfiler Profiler(M);
227   if (Profiler.instrumentFunction(F))
228     return PreservedAnalyses::none();
229   return PreservedAnalyses::all();
230 }
231 
232 ModuleMemProfilerPass::ModuleMemProfilerPass() = default;
233 
234 PreservedAnalyses ModuleMemProfilerPass::run(Module &M,
235                                              AnalysisManager<Module> &AM) {
236   ModuleMemProfiler Profiler(M);
237   if (Profiler.instrumentModule(M))
238     return PreservedAnalyses::none();
239   return PreservedAnalyses::all();
240 }
241 
242 Value *MemProfiler::memToShadow(Value *Shadow, IRBuilder<> &IRB) {
243   // (Shadow & mask) >> scale
244   Shadow = IRB.CreateAnd(Shadow, Mapping.Mask);
245   Shadow = IRB.CreateLShr(Shadow, Mapping.Scale);
246   // (Shadow >> scale) | offset
247   assert(DynamicShadowOffset);
248   return IRB.CreateAdd(Shadow, DynamicShadowOffset);
249 }
250 
251 // Instrument memset/memmove/memcpy
252 void MemProfiler::instrumentMemIntrinsic(MemIntrinsic *MI) {
253   IRBuilder<> IRB(MI);
254   if (isa<MemTransferInst>(MI)) {
255     IRB.CreateCall(
256         isa<MemMoveInst>(MI) ? MemProfMemmove : MemProfMemcpy,
257         {IRB.CreatePointerCast(MI->getOperand(0), IRB.getInt8PtrTy()),
258          IRB.CreatePointerCast(MI->getOperand(1), IRB.getInt8PtrTy()),
259          IRB.CreateIntCast(MI->getOperand(2), IntptrTy, false)});
260   } else if (isa<MemSetInst>(MI)) {
261     IRB.CreateCall(
262         MemProfMemset,
263         {IRB.CreatePointerCast(MI->getOperand(0), IRB.getInt8PtrTy()),
264          IRB.CreateIntCast(MI->getOperand(1), IRB.getInt32Ty(), false),
265          IRB.CreateIntCast(MI->getOperand(2), IntptrTy, false)});
266   }
267   MI->eraseFromParent();
268 }
269 
270 std::optional<InterestingMemoryAccess>
271 MemProfiler::isInterestingMemoryAccess(Instruction *I) const {
272   // Do not instrument the load fetching the dynamic shadow address.
273   if (DynamicShadowOffset == I)
274     return std::nullopt;
275 
276   InterestingMemoryAccess Access;
277 
278   if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
279     if (!ClInstrumentReads)
280       return std::nullopt;
281     Access.IsWrite = false;
282     Access.AccessTy = LI->getType();
283     Access.Addr = LI->getPointerOperand();
284   } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
285     if (!ClInstrumentWrites)
286       return std::nullopt;
287     Access.IsWrite = true;
288     Access.AccessTy = SI->getValueOperand()->getType();
289     Access.Addr = SI->getPointerOperand();
290   } else if (AtomicRMWInst *RMW = dyn_cast<AtomicRMWInst>(I)) {
291     if (!ClInstrumentAtomics)
292       return std::nullopt;
293     Access.IsWrite = true;
294     Access.AccessTy = RMW->getValOperand()->getType();
295     Access.Addr = RMW->getPointerOperand();
296   } else if (AtomicCmpXchgInst *XCHG = dyn_cast<AtomicCmpXchgInst>(I)) {
297     if (!ClInstrumentAtomics)
298       return std::nullopt;
299     Access.IsWrite = true;
300     Access.AccessTy = XCHG->getCompareOperand()->getType();
301     Access.Addr = XCHG->getPointerOperand();
302   } else if (auto *CI = dyn_cast<CallInst>(I)) {
303     auto *F = CI->getCalledFunction();
304     if (F && (F->getIntrinsicID() == Intrinsic::masked_load ||
305               F->getIntrinsicID() == Intrinsic::masked_store)) {
306       unsigned OpOffset = 0;
307       if (F->getIntrinsicID() == Intrinsic::masked_store) {
308         if (!ClInstrumentWrites)
309           return std::nullopt;
310         // Masked store has an initial operand for the value.
311         OpOffset = 1;
312         Access.AccessTy = CI->getArgOperand(0)->getType();
313         Access.IsWrite = true;
314       } else {
315         if (!ClInstrumentReads)
316           return std::nullopt;
317         Access.AccessTy = CI->getType();
318         Access.IsWrite = false;
319       }
320 
321       auto *BasePtr = CI->getOperand(0 + OpOffset);
322       Access.MaybeMask = CI->getOperand(2 + OpOffset);
323       Access.Addr = BasePtr;
324     }
325   }
326 
327   if (!Access.Addr)
328     return std::nullopt;
329 
330   // Do not instrument accesses from different address spaces; we cannot deal
331   // with them.
332   Type *PtrTy = cast<PointerType>(Access.Addr->getType()->getScalarType());
333   if (PtrTy->getPointerAddressSpace() != 0)
334     return std::nullopt;
335 
336   // Ignore swifterror addresses.
337   // swifterror memory addresses are mem2reg promoted by instruction
338   // selection. As such they cannot have regular uses like an instrumentation
339   // function and it makes no sense to track them as memory.
340   if (Access.Addr->isSwiftError())
341     return std::nullopt;
342 
343   // Peel off GEPs and BitCasts.
344   auto *Addr = Access.Addr->stripInBoundsOffsets();
345 
346   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
347     // Do not instrument PGO counter updates.
348     if (GV->hasSection()) {
349       StringRef SectionName = GV->getSection();
350       // Check if the global is in the PGO counters section.
351       auto OF = Triple(I->getModule()->getTargetTriple()).getObjectFormat();
352       if (SectionName.endswith(
353               getInstrProfSectionName(IPSK_cnts, OF, /*AddSegmentInfo=*/false)))
354         return std::nullopt;
355     }
356 
357     // Do not instrument accesses to LLVM internal variables.
358     if (GV->getName().startswith("__llvm"))
359       return std::nullopt;
360   }
361 
362   const DataLayout &DL = I->getModule()->getDataLayout();
363   Access.TypeSize = DL.getTypeStoreSizeInBits(Access.AccessTy);
364   return Access;
365 }
366 
367 void MemProfiler::instrumentMaskedLoadOrStore(const DataLayout &DL, Value *Mask,
368                                               Instruction *I, Value *Addr,
369                                               Type *AccessTy, bool IsWrite) {
370   auto *VTy = cast<FixedVectorType>(AccessTy);
371   uint64_t ElemTypeSize = DL.getTypeStoreSizeInBits(VTy->getScalarType());
372   unsigned Num = VTy->getNumElements();
373   auto *Zero = ConstantInt::get(IntptrTy, 0);
374   for (unsigned Idx = 0; Idx < Num; ++Idx) {
375     Value *InstrumentedAddress = nullptr;
376     Instruction *InsertBefore = I;
377     if (auto *Vector = dyn_cast<ConstantVector>(Mask)) {
378       // dyn_cast as we might get UndefValue
379       if (auto *Masked = dyn_cast<ConstantInt>(Vector->getOperand(Idx))) {
380         if (Masked->isZero())
381           // Mask is constant false, so no instrumentation needed.
382           continue;
383         // If we have a true or undef value, fall through to instrumentAddress.
384         // with InsertBefore == I
385       }
386     } else {
387       IRBuilder<> IRB(I);
388       Value *MaskElem = IRB.CreateExtractElement(Mask, Idx);
389       Instruction *ThenTerm = SplitBlockAndInsertIfThen(MaskElem, I, false);
390       InsertBefore = ThenTerm;
391     }
392 
393     IRBuilder<> IRB(InsertBefore);
394     InstrumentedAddress =
395         IRB.CreateGEP(VTy, Addr, {Zero, ConstantInt::get(IntptrTy, Idx)});
396     instrumentAddress(I, InsertBefore, InstrumentedAddress, ElemTypeSize,
397                       IsWrite);
398   }
399 }
400 
401 void MemProfiler::instrumentMop(Instruction *I, const DataLayout &DL,
402                                 InterestingMemoryAccess &Access) {
403   // Skip instrumentation of stack accesses unless requested.
404   if (!ClStack && isa<AllocaInst>(getUnderlyingObject(Access.Addr))) {
405     if (Access.IsWrite)
406       ++NumSkippedStackWrites;
407     else
408       ++NumSkippedStackReads;
409     return;
410   }
411 
412   if (Access.IsWrite)
413     NumInstrumentedWrites++;
414   else
415     NumInstrumentedReads++;
416 
417   if (Access.MaybeMask) {
418     instrumentMaskedLoadOrStore(DL, Access.MaybeMask, I, Access.Addr,
419                                 Access.AccessTy, Access.IsWrite);
420   } else {
421     // Since the access counts will be accumulated across the entire allocation,
422     // we only update the shadow access count for the first location and thus
423     // don't need to worry about alignment and type size.
424     instrumentAddress(I, I, Access.Addr, Access.TypeSize, Access.IsWrite);
425   }
426 }
427 
428 void MemProfiler::instrumentAddress(Instruction *OrigIns,
429                                     Instruction *InsertBefore, Value *Addr,
430                                     uint32_t TypeSize, bool IsWrite) {
431   IRBuilder<> IRB(InsertBefore);
432   Value *AddrLong = IRB.CreatePointerCast(Addr, IntptrTy);
433 
434   if (ClUseCalls) {
435     IRB.CreateCall(MemProfMemoryAccessCallback[IsWrite], AddrLong);
436     return;
437   }
438 
439   // Create an inline sequence to compute shadow location, and increment the
440   // value by one.
441   Type *ShadowTy = Type::getInt64Ty(*C);
442   Type *ShadowPtrTy = PointerType::get(ShadowTy, 0);
443   Value *ShadowPtr = memToShadow(AddrLong, IRB);
444   Value *ShadowAddr = IRB.CreateIntToPtr(ShadowPtr, ShadowPtrTy);
445   Value *ShadowValue = IRB.CreateLoad(ShadowTy, ShadowAddr);
446   Value *Inc = ConstantInt::get(Type::getInt64Ty(*C), 1);
447   ShadowValue = IRB.CreateAdd(ShadowValue, Inc);
448   IRB.CreateStore(ShadowValue, ShadowAddr);
449 }
450 
451 // Create the variable for the profile file name.
452 void createProfileFileNameVar(Module &M) {
453   const MDString *MemProfFilename =
454       dyn_cast_or_null<MDString>(M.getModuleFlag("MemProfProfileFilename"));
455   if (!MemProfFilename)
456     return;
457   assert(!MemProfFilename->getString().empty() &&
458          "Unexpected MemProfProfileFilename metadata with empty string");
459   Constant *ProfileNameConst = ConstantDataArray::getString(
460       M.getContext(), MemProfFilename->getString(), true);
461   GlobalVariable *ProfileNameVar = new GlobalVariable(
462       M, ProfileNameConst->getType(), /*isConstant=*/true,
463       GlobalValue::WeakAnyLinkage, ProfileNameConst, MemProfFilenameVar);
464   Triple TT(M.getTargetTriple());
465   if (TT.supportsCOMDAT()) {
466     ProfileNameVar->setLinkage(GlobalValue::ExternalLinkage);
467     ProfileNameVar->setComdat(M.getOrInsertComdat(MemProfFilenameVar));
468   }
469 }
470 
471 bool ModuleMemProfiler::instrumentModule(Module &M) {
472   // Create a module constructor.
473   std::string MemProfVersion = std::to_string(LLVM_MEM_PROFILER_VERSION);
474   std::string VersionCheckName =
475       ClInsertVersionCheck ? (MemProfVersionCheckNamePrefix + MemProfVersion)
476                            : "";
477   std::tie(MemProfCtorFunction, std::ignore) =
478       createSanitizerCtorAndInitFunctions(M, MemProfModuleCtorName,
479                                           MemProfInitName, /*InitArgTypes=*/{},
480                                           /*InitArgs=*/{}, VersionCheckName);
481 
482   const uint64_t Priority = getCtorAndDtorPriority(TargetTriple);
483   appendToGlobalCtors(M, MemProfCtorFunction, Priority);
484 
485   createProfileFileNameVar(M);
486 
487   return true;
488 }
489 
490 void MemProfiler::initializeCallbacks(Module &M) {
491   IRBuilder<> IRB(*C);
492 
493   for (size_t AccessIsWrite = 0; AccessIsWrite <= 1; AccessIsWrite++) {
494     const std::string TypeStr = AccessIsWrite ? "store" : "load";
495 
496     SmallVector<Type *, 3> Args2 = {IntptrTy, IntptrTy};
497     SmallVector<Type *, 2> Args1{1, IntptrTy};
498     MemProfMemoryAccessCallbackSized[AccessIsWrite] =
499         M.getOrInsertFunction(ClMemoryAccessCallbackPrefix + TypeStr + "N",
500                               FunctionType::get(IRB.getVoidTy(), Args2, false));
501 
502     MemProfMemoryAccessCallback[AccessIsWrite] =
503         M.getOrInsertFunction(ClMemoryAccessCallbackPrefix + TypeStr,
504                               FunctionType::get(IRB.getVoidTy(), Args1, false));
505   }
506   MemProfMemmove = M.getOrInsertFunction(
507       ClMemoryAccessCallbackPrefix + "memmove", IRB.getInt8PtrTy(),
508       IRB.getInt8PtrTy(), IRB.getInt8PtrTy(), IntptrTy);
509   MemProfMemcpy = M.getOrInsertFunction(ClMemoryAccessCallbackPrefix + "memcpy",
510                                         IRB.getInt8PtrTy(), IRB.getInt8PtrTy(),
511                                         IRB.getInt8PtrTy(), IntptrTy);
512   MemProfMemset = M.getOrInsertFunction(ClMemoryAccessCallbackPrefix + "memset",
513                                         IRB.getInt8PtrTy(), IRB.getInt8PtrTy(),
514                                         IRB.getInt32Ty(), IntptrTy);
515 }
516 
517 bool MemProfiler::maybeInsertMemProfInitAtFunctionEntry(Function &F) {
518   // For each NSObject descendant having a +load method, this method is invoked
519   // by the ObjC runtime before any of the static constructors is called.
520   // Therefore we need to instrument such methods with a call to __memprof_init
521   // at the beginning in order to initialize our runtime before any access to
522   // the shadow memory.
523   // We cannot just ignore these methods, because they may call other
524   // instrumented functions.
525   if (F.getName().find(" load]") != std::string::npos) {
526     FunctionCallee MemProfInitFunction =
527         declareSanitizerInitFunction(*F.getParent(), MemProfInitName, {});
528     IRBuilder<> IRB(&F.front(), F.front().begin());
529     IRB.CreateCall(MemProfInitFunction, {});
530     return true;
531   }
532   return false;
533 }
534 
535 bool MemProfiler::insertDynamicShadowAtFunctionEntry(Function &F) {
536   IRBuilder<> IRB(&F.front().front());
537   Value *GlobalDynamicAddress = F.getParent()->getOrInsertGlobal(
538       MemProfShadowMemoryDynamicAddress, IntptrTy);
539   if (F.getParent()->getPICLevel() == PICLevel::NotPIC)
540     cast<GlobalVariable>(GlobalDynamicAddress)->setDSOLocal(true);
541   DynamicShadowOffset = IRB.CreateLoad(IntptrTy, GlobalDynamicAddress);
542   return true;
543 }
544 
545 bool MemProfiler::instrumentFunction(Function &F) {
546   if (F.getLinkage() == GlobalValue::AvailableExternallyLinkage)
547     return false;
548   if (ClDebugFunc == F.getName())
549     return false;
550   if (F.getName().startswith("__memprof_"))
551     return false;
552 
553   bool FunctionModified = false;
554 
555   // If needed, insert __memprof_init.
556   // This function needs to be called even if the function body is not
557   // instrumented.
558   if (maybeInsertMemProfInitAtFunctionEntry(F))
559     FunctionModified = true;
560 
561   LLVM_DEBUG(dbgs() << "MEMPROF instrumenting:\n" << F << "\n");
562 
563   initializeCallbacks(*F.getParent());
564 
565   SmallVector<Instruction *, 16> ToInstrument;
566 
567   // Fill the set of memory operations to instrument.
568   for (auto &BB : F) {
569     for (auto &Inst : BB) {
570       if (isInterestingMemoryAccess(&Inst) || isa<MemIntrinsic>(Inst))
571         ToInstrument.push_back(&Inst);
572     }
573   }
574 
575   if (ToInstrument.empty()) {
576     LLVM_DEBUG(dbgs() << "MEMPROF done instrumenting: " << FunctionModified
577                       << " " << F << "\n");
578 
579     return FunctionModified;
580   }
581 
582   FunctionModified |= insertDynamicShadowAtFunctionEntry(F);
583 
584   int NumInstrumented = 0;
585   for (auto *Inst : ToInstrument) {
586     if (ClDebugMin < 0 || ClDebugMax < 0 ||
587         (NumInstrumented >= ClDebugMin && NumInstrumented <= ClDebugMax)) {
588       std::optional<InterestingMemoryAccess> Access =
589           isInterestingMemoryAccess(Inst);
590       if (Access)
591         instrumentMop(Inst, F.getParent()->getDataLayout(), *Access);
592       else
593         instrumentMemIntrinsic(cast<MemIntrinsic>(Inst));
594     }
595     NumInstrumented++;
596   }
597 
598   if (NumInstrumented > 0)
599     FunctionModified = true;
600 
601   LLVM_DEBUG(dbgs() << "MEMPROF done instrumenting: " << FunctionModified << " "
602                     << F << "\n");
603 
604   return FunctionModified;
605 }
606