1 //===-- NVPTXCtorDtorLowering.cpp - Handle global ctors and dtors --------===// 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 /// \file 10 /// This pass creates a unified init and fini kernel with the required metadata 11 //===----------------------------------------------------------------------===// 12 13 #include "NVPTXCtorDtorLowering.h" 14 #include "MCTargetDesc/NVPTXBaseInfo.h" 15 #include "NVPTX.h" 16 #include "llvm/ADT/StringExtras.h" 17 #include "llvm/IR/Constants.h" 18 #include "llvm/IR/Function.h" 19 #include "llvm/IR/GlobalVariable.h" 20 #include "llvm/IR/IRBuilder.h" 21 #include "llvm/IR/Module.h" 22 #include "llvm/IR/Value.h" 23 #include "llvm/Pass.h" 24 #include "llvm/Support/CommandLine.h" 25 #include "llvm/Transforms/Utils/ModuleUtils.h" 26 27 using namespace llvm; 28 29 #define DEBUG_TYPE "nvptx-lower-ctor-dtor" 30 31 static cl::opt<std::string> 32 GlobalStr("nvptx-lower-global-ctor-dtor-id", 33 cl::desc("Override unique ID of ctor/dtor globals."), 34 cl::init(""), cl::Hidden); 35 36 static cl::opt<bool> 37 CreateKernels("nvptx-emit-init-fini-kernel", 38 cl::desc("Emit kernels to call ctor/dtor globals."), 39 cl::init(true), cl::Hidden); 40 41 namespace { 42 43 static std::string getHash(StringRef Str) { 44 llvm::MD5 Hasher; 45 llvm::MD5::MD5Result Hash; 46 Hasher.update(Str); 47 Hasher.final(Hash); 48 return llvm::utohexstr(Hash.low(), /*LowerCase=*/true); 49 } 50 51 static void addKernelMetadata(Module &M, GlobalValue *GV) { 52 llvm::LLVMContext &Ctx = M.getContext(); 53 54 // Get "nvvm.annotations" metadata node. 55 llvm::NamedMDNode *MD = M.getOrInsertNamedMetadata("nvvm.annotations"); 56 57 llvm::Metadata *KernelMDVals[] = { 58 llvm::ConstantAsMetadata::get(GV), llvm::MDString::get(Ctx, "kernel"), 59 llvm::ConstantAsMetadata::get( 60 llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))}; 61 62 // This kernel is only to be called single-threaded. 63 llvm::Metadata *ThreadXMDVals[] = { 64 llvm::ConstantAsMetadata::get(GV), llvm::MDString::get(Ctx, "maxntidx"), 65 llvm::ConstantAsMetadata::get( 66 llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))}; 67 llvm::Metadata *ThreadYMDVals[] = { 68 llvm::ConstantAsMetadata::get(GV), llvm::MDString::get(Ctx, "maxntidy"), 69 llvm::ConstantAsMetadata::get( 70 llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))}; 71 llvm::Metadata *ThreadZMDVals[] = { 72 llvm::ConstantAsMetadata::get(GV), llvm::MDString::get(Ctx, "maxntidz"), 73 llvm::ConstantAsMetadata::get( 74 llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))}; 75 76 llvm::Metadata *BlockMDVals[] = { 77 llvm::ConstantAsMetadata::get(GV), 78 llvm::MDString::get(Ctx, "maxclusterrank"), 79 llvm::ConstantAsMetadata::get( 80 llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))}; 81 82 // Append metadata to nvvm.annotations. 83 MD->addOperand(llvm::MDNode::get(Ctx, KernelMDVals)); 84 MD->addOperand(llvm::MDNode::get(Ctx, ThreadXMDVals)); 85 MD->addOperand(llvm::MDNode::get(Ctx, ThreadYMDVals)); 86 MD->addOperand(llvm::MDNode::get(Ctx, ThreadZMDVals)); 87 MD->addOperand(llvm::MDNode::get(Ctx, BlockMDVals)); 88 } 89 90 static Function *createInitOrFiniKernelFunction(Module &M, bool IsCtor) { 91 StringRef InitOrFiniKernelName = 92 IsCtor ? "nvptx$device$init" : "nvptx$device$fini"; 93 if (M.getFunction(InitOrFiniKernelName)) 94 return nullptr; 95 96 Function *InitOrFiniKernel = Function::createWithDefaultAttr( 97 FunctionType::get(Type::getVoidTy(M.getContext()), false), 98 GlobalValue::WeakODRLinkage, 0, InitOrFiniKernelName, &M); 99 addKernelMetadata(M, InitOrFiniKernel); 100 101 return InitOrFiniKernel; 102 } 103 104 // We create the IR required to call each callback in this section. This is 105 // equivalent to the following code. Normally, the linker would provide us with 106 // the definitions of the init and fini array sections. The 'nvlink' linker does 107 // not do this so initializing these values is done by the runtime. 108 // 109 // extern "C" void **__init_array_start = nullptr; 110 // extern "C" void **__init_array_end = nullptr; 111 // extern "C" void **__fini_array_start = nullptr; 112 // extern "C" void **__fini_array_end = nullptr; 113 // 114 // using InitCallback = void(); 115 // using FiniCallback = void(); 116 // 117 // void call_init_array_callbacks() { 118 // for (auto start = __init_array_start; start != __init_array_end; ++start) 119 // reinterpret_cast<InitCallback *>(*start)(); 120 // } 121 // 122 // void call_init_array_callbacks() { 123 // size_t fini_array_size = __fini_array_end - __fini_array_start; 124 // for (size_t i = fini_array_size; i > 0; --i) 125 // reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])(); 126 // } 127 static void createInitOrFiniCalls(Function &F, bool IsCtor) { 128 Module &M = *F.getParent(); 129 LLVMContext &C = M.getContext(); 130 131 IRBuilder<> IRB(BasicBlock::Create(C, "entry", &F)); 132 auto *LoopBB = BasicBlock::Create(C, "while.entry", &F); 133 auto *ExitBB = BasicBlock::Create(C, "while.end", &F); 134 Type *PtrTy = IRB.getPtrTy(llvm::ADDRESS_SPACE_GLOBAL); 135 136 auto *Begin = M.getOrInsertGlobal( 137 IsCtor ? "__init_array_start" : "__fini_array_start", 138 PointerType::get(C, 0), [&]() { 139 auto *GV = new GlobalVariable( 140 M, PointerType::get(C, 0), 141 /*isConstant=*/false, GlobalValue::WeakAnyLinkage, 142 Constant::getNullValue(PointerType::get(C, 0)), 143 IsCtor ? "__init_array_start" : "__fini_array_start", 144 /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal, 145 /*AddressSpace=*/llvm::ADDRESS_SPACE_GLOBAL); 146 GV->setVisibility(GlobalVariable::ProtectedVisibility); 147 return GV; 148 }); 149 auto *End = M.getOrInsertGlobal( 150 IsCtor ? "__init_array_end" : "__fini_array_end", PointerType::get(C, 0), 151 [&]() { 152 auto *GV = new GlobalVariable( 153 M, PointerType::get(C, 0), 154 /*isConstant=*/false, GlobalValue::WeakAnyLinkage, 155 Constant::getNullValue(PointerType::get(C, 0)), 156 IsCtor ? "__init_array_end" : "__fini_array_end", 157 /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal, 158 /*AddressSpace=*/llvm::ADDRESS_SPACE_GLOBAL); 159 GV->setVisibility(GlobalVariable::ProtectedVisibility); 160 return GV; 161 }); 162 163 // The constructor type is suppoed to allow using the argument vectors, but 164 // for now we just call them with no arguments. 165 auto *CallBackTy = FunctionType::get(IRB.getVoidTy(), {}); 166 167 // The destructor array must be called in reverse order. Get an expression to 168 // the end of the array and iterate backwards in that case. 169 Value *BeginVal = IRB.CreateLoad(Begin->getType(), Begin, "begin"); 170 Value *EndVal = IRB.CreateLoad(Begin->getType(), End, "stop"); 171 if (!IsCtor) { 172 auto *BeginInt = IRB.CreatePtrToInt(BeginVal, IntegerType::getInt64Ty(C)); 173 auto *EndInt = IRB.CreatePtrToInt(EndVal, IntegerType::getInt64Ty(C)); 174 auto *SubInst = IRB.CreateSub(EndInt, BeginInt); 175 auto *Offset = IRB.CreateAShr( 176 SubInst, ConstantInt::get(IntegerType::getInt64Ty(C), 3), "offset", 177 /*IsExact=*/true); 178 auto *ValuePtr = IRB.CreateGEP(PointerType::get(C, 0), BeginVal, 179 ArrayRef<Value *>({Offset})); 180 EndVal = BeginVal; 181 BeginVal = IRB.CreateInBoundsGEP( 182 PointerType::get(C, 0), ValuePtr, 183 ArrayRef<Value *>(ConstantInt::get(IntegerType::getInt64Ty(C), -1)), 184 "start"); 185 } 186 IRB.CreateCondBr( 187 IRB.CreateCmp(IsCtor ? ICmpInst::ICMP_NE : ICmpInst::ICMP_UGT, BeginVal, 188 EndVal), 189 LoopBB, ExitBB); 190 IRB.SetInsertPoint(LoopBB); 191 auto *CallBackPHI = IRB.CreatePHI(PtrTy, 2, "ptr"); 192 auto *CallBack = IRB.CreateLoad(IRB.getPtrTy(F.getAddressSpace()), 193 CallBackPHI, "callback"); 194 IRB.CreateCall(CallBackTy, CallBack); 195 auto *NewCallBack = 196 IRB.CreateConstGEP1_64(PtrTy, CallBackPHI, IsCtor ? 1 : -1, "next"); 197 auto *EndCmp = IRB.CreateCmp(IsCtor ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_ULT, 198 NewCallBack, EndVal, "end"); 199 CallBackPHI->addIncoming(BeginVal, &F.getEntryBlock()); 200 CallBackPHI->addIncoming(NewCallBack, LoopBB); 201 IRB.CreateCondBr(EndCmp, ExitBB, LoopBB); 202 IRB.SetInsertPoint(ExitBB); 203 IRB.CreateRetVoid(); 204 } 205 206 static bool createInitOrFiniGlobals(Module &M, GlobalVariable *GV, 207 bool IsCtor) { 208 ConstantArray *GA = dyn_cast<ConstantArray>(GV->getInitializer()); 209 if (!GA || GA->getNumOperands() == 0) 210 return false; 211 212 // NVPTX has no way to emit variables at specific sections or support for 213 // the traditional constructor sections. Instead, we emit mangled global 214 // names so the runtime can build the list manually. 215 for (Value *V : GA->operands()) { 216 auto *CS = cast<ConstantStruct>(V); 217 auto *F = cast<Constant>(CS->getOperand(1)); 218 uint64_t Priority = cast<ConstantInt>(CS->getOperand(0))->getSExtValue(); 219 std::string PriorityStr = "." + std::to_string(Priority); 220 // We append a semi-unique hash and the priority to the global name. 221 std::string GlobalID = 222 !GlobalStr.empty() ? GlobalStr : getHash(M.getSourceFileName()); 223 std::string NameStr = 224 ((IsCtor ? "__init_array_object_" : "__fini_array_object_") + 225 F->getName() + "_" + GlobalID + "_" + std::to_string(Priority)) 226 .str(); 227 // PTX does not support exported names with '.' in them. 228 llvm::transform(NameStr, NameStr.begin(), 229 [](char c) { return c == '.' ? '_' : c; }); 230 231 auto *GV = new GlobalVariable(M, F->getType(), /*IsConstant=*/true, 232 GlobalValue::ExternalLinkage, F, NameStr, 233 nullptr, GlobalValue::NotThreadLocal, 234 /*AddressSpace=*/4); 235 // This isn't respected by Nvidia, simply put here for clarity. 236 GV->setSection(IsCtor ? ".init_array" + PriorityStr 237 : ".fini_array" + PriorityStr); 238 GV->setVisibility(GlobalVariable::ProtectedVisibility); 239 appendToUsed(M, {GV}); 240 } 241 242 return true; 243 } 244 245 static bool createInitOrFiniKernel(Module &M, StringRef GlobalName, 246 bool IsCtor) { 247 GlobalVariable *GV = M.getGlobalVariable(GlobalName); 248 if (!GV || !GV->hasInitializer()) 249 return false; 250 251 if (!createInitOrFiniGlobals(M, GV, IsCtor)) 252 return false; 253 254 if (!CreateKernels) 255 return true; 256 257 Function *InitOrFiniKernel = createInitOrFiniKernelFunction(M, IsCtor); 258 if (!InitOrFiniKernel) 259 return false; 260 261 createInitOrFiniCalls(*InitOrFiniKernel, IsCtor); 262 263 GV->eraseFromParent(); 264 return true; 265 } 266 267 static bool lowerCtorsAndDtors(Module &M) { 268 bool Modified = false; 269 Modified |= createInitOrFiniKernel(M, "llvm.global_ctors", /*IsCtor =*/true); 270 Modified |= createInitOrFiniKernel(M, "llvm.global_dtors", /*IsCtor =*/false); 271 return Modified; 272 } 273 274 class NVPTXCtorDtorLoweringLegacy final : public ModulePass { 275 public: 276 static char ID; 277 NVPTXCtorDtorLoweringLegacy() : ModulePass(ID) {} 278 bool runOnModule(Module &M) override { return lowerCtorsAndDtors(M); } 279 }; 280 281 } // End anonymous namespace 282 283 PreservedAnalyses NVPTXCtorDtorLoweringPass::run(Module &M, 284 ModuleAnalysisManager &AM) { 285 return lowerCtorsAndDtors(M) ? PreservedAnalyses::none() 286 : PreservedAnalyses::all(); 287 } 288 289 char NVPTXCtorDtorLoweringLegacy::ID = 0; 290 char &llvm::NVPTXCtorDtorLoweringLegacyPassID = NVPTXCtorDtorLoweringLegacy::ID; 291 INITIALIZE_PASS(NVPTXCtorDtorLoweringLegacy, DEBUG_TYPE, 292 "Lower ctors and dtors for NVPTX", false, false) 293 294 ModulePass *llvm::createNVPTXCtorDtorLoweringLegacyPass() { 295 return new NVPTXCtorDtorLoweringLegacy(); 296 } 297