1 //===-- AMDGPUCtorDtorLowering.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 "AMDGPUCtorDtorLowering.h" 14 #include "AMDGPU.h" 15 #include "llvm/IR/Constants.h" 16 #include "llvm/IR/Function.h" 17 #include "llvm/IR/GlobalVariable.h" 18 #include "llvm/IR/IRBuilder.h" 19 #include "llvm/IR/Module.h" 20 #include "llvm/IR/Value.h" 21 #include "llvm/Pass.h" 22 #include "llvm/Transforms/Utils/ModuleUtils.h" 23 24 using namespace llvm; 25 26 #define DEBUG_TYPE "amdgpu-lower-ctor-dtor" 27 28 namespace { 29 30 static Function *createInitOrFiniKernelFunction(Module &M, bool IsCtor) { 31 StringRef InitOrFiniKernelName = "amdgcn.device.init"; 32 if (!IsCtor) 33 InitOrFiniKernelName = "amdgcn.device.fini"; 34 if (M.getFunction(InitOrFiniKernelName)) 35 return nullptr; 36 37 Function *InitOrFiniKernel = Function::createWithDefaultAttr( 38 FunctionType::get(Type::getVoidTy(M.getContext()), false), 39 GlobalValue::WeakODRLinkage, 0, InitOrFiniKernelName, &M); 40 InitOrFiniKernel->setCallingConv(CallingConv::AMDGPU_KERNEL); 41 InitOrFiniKernel->addFnAttr("amdgpu-flat-work-group-size", "1,1"); 42 if (IsCtor) 43 InitOrFiniKernel->addFnAttr("device-init"); 44 else 45 InitOrFiniKernel->addFnAttr("device-fini"); 46 return InitOrFiniKernel; 47 } 48 49 // The linker will provide the associated symbols to allow us to traverse the 50 // global constructors / destructors in priority order. We create the IR 51 // required to call each callback in this section. This is equivalent to the 52 // following code. 53 // 54 // extern "C" void * __init_array_start[]; 55 // extern "C" void * __init_array_end[]; 56 // extern "C" void * __fini_array_start[]; 57 // extern "C" void * __fini_array_end[]; 58 // 59 // using InitCallback = void(); 60 // using FiniCallback = void(void); 61 // 62 // void call_init_array_callbacks() { 63 // for (auto start = __init_array_start; start != __init_array_end; ++start) 64 // reinterpret_cast<InitCallback *>(*start)(); 65 // } 66 // 67 // void call_fini_array_callbacks() { 68 // size_t fini_array_size = __fini_array_end - __fini_array_start; 69 // for (size_t i = fini_array_size; i > 0; --i) 70 // reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])(); 71 // } 72 static void createInitOrFiniCalls(Function &F, bool IsCtor) { 73 Module &M = *F.getParent(); 74 LLVMContext &C = M.getContext(); 75 76 IRBuilder<> IRB(BasicBlock::Create(C, "entry", &F)); 77 auto *LoopBB = BasicBlock::Create(C, "while.entry", &F); 78 auto *ExitBB = BasicBlock::Create(C, "while.end", &F); 79 Type *PtrTy = IRB.getPtrTy(AMDGPUAS::GLOBAL_ADDRESS); 80 81 auto *Begin = M.getOrInsertGlobal( 82 IsCtor ? "__init_array_start" : "__fini_array_start", 83 ArrayType::get(PtrTy, 0), [&]() { 84 return new GlobalVariable( 85 M, ArrayType::get(PtrTy, 0), 86 /*isConstant=*/true, GlobalValue::ExternalLinkage, 87 /*Initializer=*/nullptr, 88 IsCtor ? "__init_array_start" : "__fini_array_start", 89 /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal, 90 /*AddressSpace=*/1); 91 }); 92 auto *End = M.getOrInsertGlobal( 93 IsCtor ? "__init_array_end" : "__fini_array_end", 94 ArrayType::get(PtrTy, 0), [&]() { 95 return new GlobalVariable( 96 M, ArrayType::get(PtrTy, 0), 97 /*isConstant=*/true, GlobalValue::ExternalLinkage, 98 /*Initializer=*/nullptr, 99 IsCtor ? "__init_array_end" : "__fini_array_end", 100 /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal, 101 /*AddressSpace=*/1); 102 }); 103 104 // The constructor type is suppoed to allow using the argument vectors, but 105 // for now we just call them with no arguments. 106 auto *CallBackTy = FunctionType::get(IRB.getVoidTy(), {}); 107 108 Value *Start = Begin; 109 Value *Stop = End; 110 // The destructor array must be called in reverse order. Get a constant 111 // expression to the end of the array and iterate backwards instead. 112 if (!IsCtor) { 113 Type *Int64Ty = IntegerType::getInt64Ty(C); 114 auto *EndPtr = IRB.CreatePtrToInt(End, Int64Ty); 115 auto *BeginPtr = IRB.CreatePtrToInt(Begin, Int64Ty); 116 auto *ByteSize = IRB.CreateSub(EndPtr, BeginPtr); 117 auto *Size = IRB.CreateAShr(ByteSize, ConstantInt::get(Int64Ty, 3)); 118 auto *Offset = IRB.CreateSub(Size, ConstantInt::get(Int64Ty, 1)); 119 Start = IRB.CreateInBoundsGEP( 120 ArrayType::get(IRB.getPtrTy(), 0), Begin, 121 ArrayRef<Value *>({ConstantInt::get(Int64Ty, 0), Offset})); 122 Stop = Begin; 123 } 124 125 IRB.CreateCondBr( 126 IRB.CreateCmp(IsCtor ? ICmpInst::ICMP_NE : ICmpInst::ICMP_UGE, Start, 127 Stop), 128 LoopBB, ExitBB); 129 IRB.SetInsertPoint(LoopBB); 130 auto *CallBackPHI = IRB.CreatePHI(PtrTy, 2, "ptr"); 131 auto *CallBack = IRB.CreateLoad(IRB.getPtrTy(F.getAddressSpace()), 132 CallBackPHI, "callback"); 133 IRB.CreateCall(CallBackTy, CallBack); 134 auto *NewCallBack = 135 IRB.CreateConstGEP1_64(PtrTy, CallBackPHI, IsCtor ? 1 : -1, "next"); 136 auto *EndCmp = IRB.CreateCmp(IsCtor ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_ULT, 137 NewCallBack, Stop, "end"); 138 CallBackPHI->addIncoming(Start, &F.getEntryBlock()); 139 CallBackPHI->addIncoming(NewCallBack, LoopBB); 140 IRB.CreateCondBr(EndCmp, ExitBB, LoopBB); 141 IRB.SetInsertPoint(ExitBB); 142 IRB.CreateRetVoid(); 143 } 144 145 static bool createInitOrFiniKernel(Module &M, StringRef GlobalName, 146 bool IsCtor) { 147 GlobalVariable *GV = M.getGlobalVariable(GlobalName); 148 if (!GV || !GV->hasInitializer()) 149 return false; 150 ConstantArray *GA = dyn_cast<ConstantArray>(GV->getInitializer()); 151 if (!GA || GA->getNumOperands() == 0) 152 return false; 153 154 Function *InitOrFiniKernel = createInitOrFiniKernelFunction(M, IsCtor); 155 if (!InitOrFiniKernel) 156 return false; 157 158 createInitOrFiniCalls(*InitOrFiniKernel, IsCtor); 159 160 appendToUsed(M, {InitOrFiniKernel}); 161 return true; 162 } 163 164 static bool lowerCtorsAndDtors(Module &M) { 165 bool Modified = false; 166 Modified |= createInitOrFiniKernel(M, "llvm.global_ctors", /*IsCtor =*/true); 167 Modified |= createInitOrFiniKernel(M, "llvm.global_dtors", /*IsCtor =*/false); 168 return Modified; 169 } 170 171 class AMDGPUCtorDtorLoweringLegacy final : public ModulePass { 172 public: 173 static char ID; 174 AMDGPUCtorDtorLoweringLegacy() : ModulePass(ID) {} 175 bool runOnModule(Module &M) override { return lowerCtorsAndDtors(M); } 176 }; 177 178 } // End anonymous namespace 179 180 PreservedAnalyses AMDGPUCtorDtorLoweringPass::run(Module &M, 181 ModuleAnalysisManager &AM) { 182 return lowerCtorsAndDtors(M) ? PreservedAnalyses::none() 183 : PreservedAnalyses::all(); 184 } 185 186 char AMDGPUCtorDtorLoweringLegacy::ID = 0; 187 char &llvm::AMDGPUCtorDtorLoweringLegacyPassID = 188 AMDGPUCtorDtorLoweringLegacy::ID; 189 INITIALIZE_PASS(AMDGPUCtorDtorLoweringLegacy, DEBUG_TYPE, 190 "Lower ctors and dtors for AMDGPU", false, false) 191 192 ModulePass *llvm::createAMDGPUCtorDtorLoweringLegacyPass() { 193 return new AMDGPUCtorDtorLoweringLegacy(); 194 } 195