1 //===-- InstrProfiling.cpp - Frontend instrumentation based profiling -----===//
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 pass lowers instrprof_increment intrinsics emitted by a frontend for
11 // profiling. It also builds the data structures and initialization code needed
12 // for updating execution counts and emitting the profile at runtime.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "llvm/Transforms/Instrumentation.h"
17 
18 #include "llvm/ADT/Triple.h"
19 #include "llvm/IR/IRBuilder.h"
20 #include "llvm/IR/IntrinsicInst.h"
21 #include "llvm/IR/Module.h"
22 #include "llvm/Transforms/Utils/ModuleUtils.h"
23 
24 using namespace llvm;
25 
26 #define DEBUG_TYPE "instrprof"
27 
28 namespace {
29 
30 class InstrProfiling : public ModulePass {
31 public:
32   static char ID;
33 
34   InstrProfiling() : ModulePass(ID) {}
35 
36   InstrProfiling(const InstrProfOptions &Options)
37       : ModulePass(ID), Options(Options) {}
38 
39   const char *getPassName() const override {
40     return "Frontend instrumentation-based coverage lowering";
41   }
42 
43   bool runOnModule(Module &M) override;
44 
45   void getAnalysisUsage(AnalysisUsage &AU) const override {
46     AU.setPreservesCFG();
47   }
48 
49 private:
50   InstrProfOptions Options;
51   Module *M;
52   DenseMap<GlobalVariable *, GlobalVariable *> RegionCounters;
53   std::vector<Value *> UsedVars;
54 
55   bool isMachO() const {
56     return Triple(M->getTargetTriple()).isOSBinFormatMachO();
57   }
58 
59   /// Get the section name for the counter variables.
60   StringRef getCountersSection() const {
61     return isMachO() ? "__DATA,__llvm_prf_cnts" : "__llvm_prf_cnts";
62   }
63 
64   /// Get the section name for the name variables.
65   StringRef getNameSection() const {
66     return isMachO() ? "__DATA,__llvm_prf_names" : "__llvm_prf_names";
67   }
68 
69   /// Get the section name for the profile data variables.
70   StringRef getDataSection() const {
71     return isMachO() ? "__DATA,__llvm_prf_data" : "__llvm_prf_data";
72   }
73 
74   /// Get the section name for the coverage mapping data.
75   StringRef getCoverageSection() const {
76     return isMachO() ? "__DATA,__llvm_covmap" : "__llvm_covmap";
77   }
78 
79   /// Replace instrprof_increment with an increment of the appropriate value.
80   void lowerIncrement(InstrProfIncrementInst *Inc);
81 
82   /// Set up the section and uses for coverage data and its references.
83   void lowerCoverageData(GlobalVariable *CoverageData);
84 
85   /// Get the region counters for an increment, creating them if necessary.
86   ///
87   /// If the counter array doesn't yet exist, the profile data variables
88   /// referring to them will also be created.
89   GlobalVariable *getOrCreateRegionCounters(InstrProfIncrementInst *Inc);
90 
91   /// Emit runtime registration functions for each profile data variable.
92   void emitRegistration();
93 
94   /// Emit the necessary plumbing to pull in the runtime initialization.
95   void emitRuntimeHook();
96 
97   /// Add uses of our data variables and runtime hook.
98   void emitUses();
99 
100   /// Create a static initializer for our data, on platforms that need it.
101   void emitInitialization();
102 };
103 
104 } // anonymous namespace
105 
106 char InstrProfiling::ID = 0;
107 INITIALIZE_PASS(InstrProfiling, "instrprof",
108                 "Frontend instrumentation-based coverage lowering.", false,
109                 false)
110 
111 ModulePass *llvm::createInstrProfilingPass(const InstrProfOptions &Options) {
112   return new InstrProfiling(Options);
113 }
114 
115 bool InstrProfiling::runOnModule(Module &M) {
116   bool MadeChange = false;
117 
118   this->M = &M;
119   RegionCounters.clear();
120   UsedVars.clear();
121 
122   for (Function &F : M)
123     for (BasicBlock &BB : F)
124       for (auto I = BB.begin(), E = BB.end(); I != E;)
125         if (auto *Inc = dyn_cast<InstrProfIncrementInst>(I++)) {
126           lowerIncrement(Inc);
127           MadeChange = true;
128         }
129   if (GlobalVariable *Coverage = M.getNamedGlobal("__llvm_coverage_mapping")) {
130     lowerCoverageData(Coverage);
131     MadeChange = true;
132   }
133   if (!MadeChange)
134     return false;
135 
136   emitRegistration();
137   emitRuntimeHook();
138   emitUses();
139   emitInitialization();
140   return true;
141 }
142 
143 void InstrProfiling::lowerIncrement(InstrProfIncrementInst *Inc) {
144   GlobalVariable *Counters = getOrCreateRegionCounters(Inc);
145 
146   IRBuilder<> Builder(Inc->getParent(), *Inc);
147   uint64_t Index = Inc->getIndex()->getZExtValue();
148   llvm::Value *Addr = Builder.CreateConstInBoundsGEP2_64(Counters, 0, Index);
149   llvm::Value *Count = Builder.CreateLoad(Addr, "pgocount");
150   Count = Builder.CreateAdd(Count, Builder.getInt64(1));
151   Inc->replaceAllUsesWith(Builder.CreateStore(Count, Addr));
152   Inc->eraseFromParent();
153 }
154 
155 void InstrProfiling::lowerCoverageData(GlobalVariable *CoverageData) {
156   CoverageData->setSection(getCoverageSection());
157   CoverageData->setAlignment(8);
158 
159   Constant *Init = CoverageData->getInitializer();
160   // We're expecting { i32, i32, i32, i32, [n x { i8*, i32, i32 }], [m x i8] }
161   // for some C. If not, the frontend's given us something broken.
162   assert(Init->getNumOperands() == 6 && "bad number of fields in coverage map");
163   assert(isa<ConstantArray>(Init->getAggregateElement(4)) &&
164          "invalid function list in coverage map");
165   ConstantArray *Records = cast<ConstantArray>(Init->getAggregateElement(4));
166   for (unsigned I = 0, E = Records->getNumOperands(); I < E; ++I) {
167     Constant *Record = Records->getOperand(I);
168     Value *V = const_cast<Value *>(Record->getOperand(0))->stripPointerCasts();
169 
170     assert(isa<GlobalVariable>(V) && "Missing reference to function name");
171     GlobalVariable *Name = cast<GlobalVariable>(V);
172 
173     // If we have region counters for this name, we've already handled it.
174     auto It = RegionCounters.find(Name);
175     if (It != RegionCounters.end())
176       continue;
177 
178     // Move the name variable to the right section.
179     Name->setSection(getNameSection());
180     Name->setAlignment(1);
181   }
182 }
183 
184 /// Get the name of a profiling variable for a particular function.
185 static std::string getVarName(InstrProfIncrementInst *Inc, StringRef VarName) {
186   auto *Arr = cast<ConstantDataArray>(Inc->getName()->getInitializer());
187   StringRef Name = Arr->isCString() ? Arr->getAsCString() : Arr->getAsString();
188   return ("__llvm_profile_" + VarName + "_" + Name).str();
189 }
190 
191 GlobalVariable *
192 InstrProfiling::getOrCreateRegionCounters(InstrProfIncrementInst *Inc) {
193   GlobalVariable *Name = Inc->getName();
194   auto It = RegionCounters.find(Name);
195   if (It != RegionCounters.end())
196     return It->second;
197 
198   // Move the name variable to the right section.
199   Name->setSection(getNameSection());
200   Name->setAlignment(1);
201 
202   uint64_t NumCounters = Inc->getNumCounters()->getZExtValue();
203   LLVMContext &Ctx = M->getContext();
204   ArrayType *CounterTy = ArrayType::get(Type::getInt64Ty(Ctx), NumCounters);
205 
206   // Create the counters variable.
207   auto *Counters = new GlobalVariable(*M, CounterTy, false, Name->getLinkage(),
208                                       Constant::getNullValue(CounterTy),
209                                       getVarName(Inc, "counters"));
210   Counters->setVisibility(Name->getVisibility());
211   Counters->setSection(getCountersSection());
212   Counters->setAlignment(8);
213 
214   RegionCounters[Inc->getName()] = Counters;
215 
216   // Create data variable.
217   auto *NameArrayTy = Name->getType()->getPointerElementType();
218   auto *Int32Ty = Type::getInt32Ty(Ctx);
219   auto *Int64Ty = Type::getInt64Ty(Ctx);
220   auto *Int8PtrTy = Type::getInt8PtrTy(Ctx);
221   auto *Int64PtrTy = Type::getInt64PtrTy(Ctx);
222 
223   Type *DataTypes[] = {Int32Ty, Int32Ty, Int64Ty, Int8PtrTy, Int64PtrTy};
224   auto *DataTy = StructType::get(Ctx, makeArrayRef(DataTypes));
225   Constant *DataVals[] = {
226       ConstantInt::get(Int32Ty, NameArrayTy->getArrayNumElements()),
227       ConstantInt::get(Int32Ty, NumCounters),
228       ConstantInt::get(Int64Ty, Inc->getHash()->getZExtValue()),
229       ConstantExpr::getBitCast(Name, Int8PtrTy),
230       ConstantExpr::getBitCast(Counters, Int64PtrTy)};
231   auto *Data = new GlobalVariable(*M, DataTy, true, Name->getLinkage(),
232                                   ConstantStruct::get(DataTy, DataVals),
233                                   getVarName(Inc, "data"));
234   Data->setVisibility(Name->getVisibility());
235   Data->setSection(getDataSection());
236   Data->setAlignment(8);
237 
238   // Mark the data variable as used so that it isn't stripped out.
239   UsedVars.push_back(Data);
240 
241   return Counters;
242 }
243 
244 void InstrProfiling::emitRegistration() {
245   // Don't do this for Darwin.  compiler-rt uses linker magic.
246   if (Triple(M->getTargetTriple()).isOSDarwin())
247     return;
248 
249   // Construct the function.
250   auto *VoidTy = Type::getVoidTy(M->getContext());
251   auto *VoidPtrTy = Type::getInt8PtrTy(M->getContext());
252   auto *RegisterFTy = FunctionType::get(VoidTy, false);
253   auto *RegisterF = Function::Create(RegisterFTy, GlobalValue::InternalLinkage,
254                                      "__llvm_profile_register_functions", M);
255   RegisterF->setUnnamedAddr(true);
256   if (Options.NoRedZone)
257     RegisterF->addFnAttr(Attribute::NoRedZone);
258 
259   auto *RuntimeRegisterTy = llvm::FunctionType::get(VoidTy, VoidPtrTy, false);
260   auto *RuntimeRegisterF =
261       Function::Create(RuntimeRegisterTy, GlobalVariable::ExternalLinkage,
262                        "__llvm_profile_register_function", M);
263 
264   IRBuilder<> IRB(BasicBlock::Create(M->getContext(), "", RegisterF));
265   for (Value *Data : UsedVars)
266     IRB.CreateCall(RuntimeRegisterF, IRB.CreateBitCast(Data, VoidPtrTy));
267   IRB.CreateRetVoid();
268 }
269 
270 void InstrProfiling::emitRuntimeHook() {
271   const char *const RuntimeVarName = "__llvm_profile_runtime";
272   const char *const RuntimeUserName = "__llvm_profile_runtime_user";
273 
274   // If the module's provided its own runtime, we don't need to do anything.
275   if (M->getGlobalVariable(RuntimeVarName))
276     return;
277 
278   // Declare an external variable that will pull in the runtime initialization.
279   auto *Int32Ty = Type::getInt32Ty(M->getContext());
280   auto *Var =
281       new GlobalVariable(*M, Int32Ty, false, GlobalValue::ExternalLinkage,
282                          nullptr, RuntimeVarName);
283 
284   // Make a function that uses it.
285   auto *User =
286       Function::Create(FunctionType::get(Int32Ty, false),
287                        GlobalValue::LinkOnceODRLinkage, RuntimeUserName, M);
288   User->addFnAttr(Attribute::NoInline);
289   if (Options.NoRedZone)
290     User->addFnAttr(Attribute::NoRedZone);
291   User->setVisibility(GlobalValue::HiddenVisibility);
292 
293   IRBuilder<> IRB(BasicBlock::Create(M->getContext(), "", User));
294   auto *Load = IRB.CreateLoad(Var);
295   IRB.CreateRet(Load);
296 
297   // Mark the user variable as used so that it isn't stripped out.
298   UsedVars.push_back(User);
299 }
300 
301 void InstrProfiling::emitUses() {
302   if (UsedVars.empty())
303     return;
304 
305   GlobalVariable *LLVMUsed = M->getGlobalVariable("llvm.used");
306   std::vector<Constant*> MergedVars;
307   if (LLVMUsed) {
308     // Collect the existing members of llvm.used.
309     ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
310     for (unsigned I = 0, E = Inits->getNumOperands(); I != E; ++I)
311       MergedVars.push_back(Inits->getOperand(I));
312     LLVMUsed->eraseFromParent();
313   }
314 
315   Type *i8PTy = Type::getInt8PtrTy(M->getContext());
316   // Add uses for our data.
317   for (auto *Value : UsedVars)
318     MergedVars.push_back(
319         ConstantExpr::getBitCast(cast<llvm::Constant>(Value), i8PTy));
320 
321   // Recreate llvm.used.
322   ArrayType *ATy = ArrayType::get(i8PTy, MergedVars.size());
323   LLVMUsed = new llvm::GlobalVariable(
324       *M, ATy, false, llvm::GlobalValue::AppendingLinkage,
325       llvm::ConstantArray::get(ATy, MergedVars), "llvm.used");
326 
327   LLVMUsed->setSection("llvm.metadata");
328 }
329 
330 void InstrProfiling::emitInitialization() {
331   Constant *RegisterF = M->getFunction("__llvm_profile_register_functions");
332   if (!RegisterF)
333     return;
334 
335   // Create the initialization function.
336   auto *VoidTy = Type::getVoidTy(M->getContext());
337   auto *F =
338       Function::Create(FunctionType::get(VoidTy, false),
339                        GlobalValue::InternalLinkage, "__llvm_profile_init", M);
340   F->setUnnamedAddr(true);
341   F->addFnAttr(Attribute::NoInline);
342   if (Options.NoRedZone)
343     F->addFnAttr(Attribute::NoRedZone);
344 
345   // Add the basic block and the necessary calls.
346   IRBuilder<> IRB(BasicBlock::Create(M->getContext(), "", F));
347   IRB.CreateCall(RegisterF);
348   IRB.CreateRetVoid();
349 
350   appendToGlobalCtors(*M, F, 0);
351 }
352