1 //===------ PerfMonitor.cpp - Generate a run-time performance monitor. -======//
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 //===----------------------------------------------------------------------===//
11 
12 #include "polly/CodeGen/PerfMonitor.h"
13 #include "polly/CodeGen/RuntimeDebugBuilder.h"
14 #include "polly/ScopInfo.h"
15 #include "llvm/ADT/Triple.h"
16 #include "llvm/IR/Intrinsics.h"
17 #include <sstream>
18 
19 using namespace llvm;
20 using namespace polly;
21 
22 Function *PerfMonitor::getAtExit() {
23   const char *Name = "atexit";
24   Function *F = M->getFunction(Name);
25 
26   if (!F) {
27     GlobalValue::LinkageTypes Linkage = Function::ExternalLinkage;
28     FunctionType *Ty = FunctionType::get(Builder.getInt32Ty(),
29                                          {Builder.getInt8PtrTy()}, false);
30     F = Function::Create(Ty, Linkage, Name, M);
31   }
32 
33   return F;
34 }
35 
36 void PerfMonitor::addToGlobalConstructors(Function *Fn) {
37   const char *Name = "llvm.global_ctors";
38   GlobalVariable *GV = M->getGlobalVariable(Name);
39   std::vector<Constant *> V;
40 
41   if (GV) {
42     Constant *Array = GV->getInitializer();
43     for (Value *X : Array->operand_values())
44       V.push_back(cast<Constant>(X));
45     GV->eraseFromParent();
46   }
47 
48   StructType *ST = StructType::get(Builder.getInt32Ty(), Fn->getType(),
49                                    Builder.getInt8PtrTy());
50 
51   V.push_back(
52       ConstantStruct::get(ST, Builder.getInt32(10), Fn,
53                           ConstantPointerNull::get(Builder.getInt8PtrTy())));
54   ArrayType *Ty = ArrayType::get(ST, V.size());
55 
56   GV = new GlobalVariable(*M, Ty, true, GlobalValue::AppendingLinkage,
57                           ConstantArray::get(Ty, V), Name, nullptr,
58                           GlobalVariable::NotThreadLocal);
59 }
60 
61 Function *PerfMonitor::getRDTSCP() {
62   return Intrinsic::getDeclaration(M, Intrinsic::x86_rdtscp);
63 }
64 
65 PerfMonitor::PerfMonitor(const Scop &S, Module *M)
66     : M(M), Builder(M->getContext()), S(S) {
67   if (Triple(M->getTargetTriple()).getArch() == llvm::Triple::x86_64)
68     Supported = true;
69   else
70     Supported = false;
71 }
72 
73 static void TryRegisterGlobal(Module *M, const char *Name,
74                               Constant *InitialValue, Value **Location) {
75   *Location = M->getGlobalVariable(Name);
76 
77   if (!*Location)
78     *Location = new GlobalVariable(
79         *M, InitialValue->getType(), true, GlobalValue::WeakAnyLinkage,
80         InitialValue, Name, nullptr, GlobalVariable::InitialExecTLSModel);
81 };
82 
83 // Generate a unique name that is usable as a LLVM name for a scop to name its
84 // performance counter.
85 static std::string GetScopUniqueVarname(const Scop &S) {
86   std::stringstream Name;
87   std::string EntryString, ExitString;
88   std::tie(EntryString, ExitString) = S.getEntryExitStr();
89 
90   Name << "__polly_perf_cycles_in_" << std::string(S.getFunction().getName())
91        << "_from__" << EntryString << "__to__" << ExitString;
92   return Name.str();
93 }
94 
95 void PerfMonitor::addScopCounter() {
96   const std::string varname = GetScopUniqueVarname(S);
97   TryRegisterGlobal(M, varname.c_str(), Builder.getInt64(0),
98                     &CyclesInCurrentScopPtr);
99 }
100 
101 void PerfMonitor::addGlobalVariables() {
102   TryRegisterGlobal(M, "__polly_perf_cycles_total_start", Builder.getInt64(0),
103                     &CyclesTotalStartPtr);
104 
105   TryRegisterGlobal(M, "__polly_perf_initialized", Builder.getInt1(0),
106                     &AlreadyInitializedPtr);
107 
108   TryRegisterGlobal(M, "__polly_perf_cycles_in_scops", Builder.getInt64(0),
109                     &CyclesInScopsPtr);
110 
111   TryRegisterGlobal(M, "__polly_perf_cycles_in_scop_start", Builder.getInt64(0),
112                     &CyclesInScopStartPtr);
113 
114   TryRegisterGlobal(M, "__polly_perf_write_loation", Builder.getInt32(0),
115                     &RDTSCPWriteLocation);
116 }
117 
118 static const char *InitFunctionName = "__polly_perf_init";
119 static const char *FinalReportingFunctionName = "__polly_perf_final";
120 
121 static BasicBlock *FinalStartBB = nullptr;
122 static ReturnInst *ReturnFromFinal = nullptr;
123 
124 Function *PerfMonitor::insertFinalReporting() {
125   // Create new function.
126   GlobalValue::LinkageTypes Linkage = Function::WeakODRLinkage;
127   FunctionType *Ty = FunctionType::get(Builder.getVoidTy(), {}, false);
128   Function *ExitFn =
129       Function::Create(Ty, Linkage, FinalReportingFunctionName, M);
130   FinalStartBB = BasicBlock::Create(M->getContext(), "start", ExitFn);
131   Builder.SetInsertPoint(FinalStartBB);
132 
133   if (!Supported) {
134     RuntimeDebugBuilder::createCPUPrinter(
135         Builder, "Polly runtime information generation not supported\n");
136     Builder.CreateRetVoid();
137     return ExitFn;
138   }
139 
140   // Measure current cycles and compute final timings.
141   Function *RDTSCPFn = getRDTSCP();
142   Value *CurrentCycles = Builder.CreateCall(
143       RDTSCPFn,
144       Builder.CreatePointerCast(RDTSCPWriteLocation, Builder.getInt8PtrTy()));
145   Value *CyclesStart = Builder.CreateLoad(CyclesTotalStartPtr, true);
146   Value *CyclesTotal = Builder.CreateSub(CurrentCycles, CyclesStart);
147   Value *CyclesInScops = Builder.CreateLoad(CyclesInScopsPtr, true);
148 
149   // Print the runtime information.
150   RuntimeDebugBuilder::createCPUPrinter(Builder, "Polly runtime information\n");
151   RuntimeDebugBuilder::createCPUPrinter(Builder, "-------------------------\n");
152   RuntimeDebugBuilder::createCPUPrinter(Builder, "Total: ", CyclesTotal, "\n");
153   RuntimeDebugBuilder::createCPUPrinter(Builder, "Scops: ", CyclesInScops,
154                                         "\n");
155   ReturnFromFinal = Builder.CreateRetVoid();
156   return ExitFn;
157 }
158 
159 void PerfMonitor::AppendScopReporting() {
160   Builder.SetInsertPoint(FinalStartBB);
161   ReturnFromFinal->eraseFromParent();
162 
163   Value *CyclesInCurrentScop =
164       Builder.CreateLoad(this->CyclesInCurrentScopPtr, true);
165   std::string EntryName, ExitName;
166   std::tie(EntryName, ExitName) = S.getEntryExitStr();
167 
168   RuntimeDebugBuilder::createCPUPrinter(
169       Builder, "Scop(", S.getFunction().getName(), " |from: ", EntryName,
170       " |to: ", ExitName, "): ", CyclesInCurrentScop, "\n");
171 
172   ReturnFromFinal = Builder.CreateRetVoid();
173 }
174 
175 static Function *FinalReporting = nullptr;
176 
177 void PerfMonitor::initialize() {
178   addGlobalVariables();
179   addScopCounter();
180 
181   // Ensure that we only add the final reporting function once.
182   // On later invocations, append to the reporting function.
183   if (!FinalReporting) {
184     FinalReporting = insertFinalReporting();
185 
186     Function *InitFn = insertInitFunction(FinalReporting);
187     addToGlobalConstructors(InitFn);
188   }
189 
190   AppendScopReporting();
191 }
192 
193 Function *PerfMonitor::insertInitFunction(Function *FinalReporting) {
194   // Insert function definition and BBs.
195   GlobalValue::LinkageTypes Linkage = Function::WeakODRLinkage;
196   FunctionType *Ty = FunctionType::get(Builder.getVoidTy(), {}, false);
197   Function *InitFn = Function::Create(Ty, Linkage, InitFunctionName, M);
198   BasicBlock *Start = BasicBlock::Create(M->getContext(), "start", InitFn);
199   BasicBlock *EarlyReturn =
200       BasicBlock::Create(M->getContext(), "earlyreturn", InitFn);
201   BasicBlock *InitBB = BasicBlock::Create(M->getContext(), "initbb", InitFn);
202 
203   Builder.SetInsertPoint(Start);
204 
205   // Check if this function was already run. If yes, return.
206   //
207   // In case profiling has been enabled in multiple translation units, the
208   // initializer function will be added to the global constructors list of
209   // each translation unit. When merging translation units, the global
210   // constructor lists are just appended, such that the initializer will appear
211   // multiple times. To avoid initializations being run multiple times (and
212   // especially to avoid that atExitFn is called more than once), we bail
213   // out if the intializer is run more than once.
214   Value *HasRunBefore = Builder.CreateLoad(AlreadyInitializedPtr);
215   Builder.CreateCondBr(HasRunBefore, EarlyReturn, InitBB);
216   Builder.SetInsertPoint(EarlyReturn);
217   Builder.CreateRetVoid();
218 
219   // Keep track that this function has been run once.
220   Builder.SetInsertPoint(InitBB);
221   Value *True = Builder.getInt1(true);
222   Builder.CreateStore(True, AlreadyInitializedPtr);
223 
224   // Register the final reporting function with atexit().
225   Value *FinalReportingPtr =
226       Builder.CreatePointerCast(FinalReporting, Builder.getInt8PtrTy());
227   Function *AtExitFn = getAtExit();
228   Builder.CreateCall(AtExitFn, {FinalReportingPtr});
229 
230   if (Supported) {
231     // Read the currently cycle counter and store the result for later.
232     Function *RDTSCPFn = getRDTSCP();
233     Value *CurrentCycles = Builder.CreateCall(
234         RDTSCPFn,
235         Builder.CreatePointerCast(RDTSCPWriteLocation, Builder.getInt8PtrTy()));
236     Builder.CreateStore(CurrentCycles, CyclesTotalStartPtr, true);
237   }
238   Builder.CreateRetVoid();
239 
240   return InitFn;
241 }
242 
243 void PerfMonitor::insertRegionStart(Instruction *InsertBefore) {
244   if (!Supported)
245     return;
246 
247   Builder.SetInsertPoint(InsertBefore);
248   Function *RDTSCPFn = getRDTSCP();
249   Value *CurrentCycles = Builder.CreateCall(
250       RDTSCPFn,
251       Builder.CreatePointerCast(RDTSCPWriteLocation, Builder.getInt8PtrTy()));
252   Builder.CreateStore(CurrentCycles, CyclesInScopStartPtr, true);
253 }
254 
255 void PerfMonitor::insertRegionEnd(Instruction *InsertBefore) {
256   if (!Supported)
257     return;
258 
259   Builder.SetInsertPoint(InsertBefore);
260   Function *RDTSCPFn = getRDTSCP();
261   LoadInst *CyclesStart = Builder.CreateLoad(CyclesInScopStartPtr, true);
262   Value *CurrentCycles = Builder.CreateCall(
263       RDTSCPFn,
264       Builder.CreatePointerCast(RDTSCPWriteLocation, Builder.getInt8PtrTy()));
265   Value *CyclesInScop = Builder.CreateSub(CurrentCycles, CyclesStart);
266   Value *CyclesInScops = Builder.CreateLoad(CyclesInScopsPtr, true);
267   CyclesInScops = Builder.CreateAdd(CyclesInScops, CyclesInScop);
268   Builder.CreateStore(CyclesInScops, CyclesInScopsPtr, true);
269 
270   Value *CyclesInCurrentScop = Builder.CreateLoad(CyclesInCurrentScopPtr, true);
271   CyclesInCurrentScop = Builder.CreateAdd(CyclesInCurrentScop, CyclesInScop);
272   Builder.CreateStore(CyclesInCurrentScop, CyclesInCurrentScopPtr, true);
273 }
274