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
24using namespace llvm;
25
26#define DEBUG_TYPE "amdgpu-lower-ctor-dtor"
27
28namespace {
29
30static Function *createInitOrFiniKernelFunction(Module &M, bool IsCtor) {
31 StringRef InitOrFiniKernelName = "amdgcn.device.init";
32 if (!IsCtor)
33 InitOrFiniKernelName = "amdgcn.device.fini";
34 if (M.getFunction(Name: InitOrFiniKernelName))
35 return nullptr;
36
37 Function *InitOrFiniKernel = Function::createWithDefaultAttr(
38 Ty: FunctionType::get(Result: Type::getVoidTy(C&: M.getContext()), isVarArg: false),
39 Linkage: GlobalValue::WeakODRLinkage, AddrSpace: 0, N: InitOrFiniKernelName, M: &M);
40 InitOrFiniKernel->setCallingConv(CallingConv::AMDGPU_KERNEL);
41 InitOrFiniKernel->addFnAttr(Kind: "amdgpu-flat-work-group-size", Val: "1,1");
42 if (IsCtor)
43 InitOrFiniKernel->addFnAttr(Kind: "device-init");
44 else
45 InitOrFiniKernel->addFnAttr(Kind: "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// }
72static void createInitOrFiniCalls(Function &F, bool IsCtor) {
73 Module &M = *F.getParent();
74 LLVMContext &C = M.getContext();
75
76 IRBuilder<> IRB(BasicBlock::Create(Context&: C, Name: "entry", Parent: &F));
77 auto *LoopBB = BasicBlock::Create(Context&: C, Name: "while.entry", Parent: &F);
78 auto *ExitBB = BasicBlock::Create(Context&: C, Name: "while.end", Parent: &F);
79 Type *PtrTy = IRB.getPtrTy(AddrSpace: AMDGPUAS::GLOBAL_ADDRESS);
80 ArrayType *PtrArrayTy = ArrayType::get(ElementType: PtrTy, NumElements: 0);
81
82 auto *Begin = M.getOrInsertGlobal(
83 Name: IsCtor ? "__init_array_start" : "__fini_array_start", Ty: PtrArrayTy, CreateGlobalCallback: [&]() {
84 return new GlobalVariable(
85 M, PtrArrayTy,
86 /*isConstant=*/true, GlobalValue::ExternalLinkage,
87 /*Initializer=*/nullptr,
88 IsCtor ? "__init_array_start" : "__fini_array_start",
89 /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
90 /*AddressSpace=*/AMDGPUAS::GLOBAL_ADDRESS);
91 });
92 auto *End = M.getOrInsertGlobal(
93 Name: IsCtor ? "__init_array_end" : "__fini_array_end", Ty: PtrArrayTy, CreateGlobalCallback: [&]() {
94 return new GlobalVariable(
95 M, PtrArrayTy,
96 /*isConstant=*/true, GlobalValue::ExternalLinkage,
97 /*Initializer=*/nullptr,
98 IsCtor ? "__init_array_end" : "__fini_array_end",
99 /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
100 /*AddressSpace=*/AMDGPUAS::GLOBAL_ADDRESS);
101 });
102
103 // The constructor type is suppoed to allow using the argument vectors, but
104 // for now we just call them with no arguments.
105 auto *CallBackTy = FunctionType::get(Result: IRB.getVoidTy(), isVarArg: {});
106
107 Value *Start = Begin;
108 Value *Stop = End;
109 // The destructor array must be called in reverse order. Get a constant
110 // expression to the end of the array and iterate backwards instead.
111 if (!IsCtor) {
112 Type *Int64Ty = IntegerType::getInt64Ty(C);
113 auto *EndPtr = IRB.CreatePtrToInt(V: End, DestTy: Int64Ty);
114 auto *BeginPtr = IRB.CreatePtrToInt(V: Begin, DestTy: Int64Ty);
115 auto *ByteSize = IRB.CreateSub(LHS: EndPtr, RHS: BeginPtr, Name: "", /*HasNUW=*/true,
116 /*HasNSW=*/true);
117 auto *Size = IRB.CreateAShr(LHS: ByteSize, RHS: ConstantInt::get(Ty: Int64Ty, V: 3), Name: "",
118 /*isExact=*/true);
119 auto *Offset =
120 IRB.CreateSub(LHS: Size, RHS: ConstantInt::get(Ty: Int64Ty, V: 1), Name: "", /*HasNUW=*/true,
121 /*HasNSW=*/true);
122 Start = IRB.CreateInBoundsGEP(
123 Ty: PtrArrayTy, Ptr: Begin,
124 IdxList: ArrayRef<Value *>({ConstantInt::get(Ty: Int64Ty, V: 0), Offset}));
125 Stop = Begin;
126 }
127
128 IRB.CreateCondBr(
129 Cond: IRB.CreateCmp(Pred: IsCtor ? ICmpInst::ICMP_NE : ICmpInst::ICMP_UGE, LHS: Start,
130 RHS: Stop),
131 True: LoopBB, False: ExitBB);
132 IRB.SetInsertPoint(LoopBB);
133 auto *CallBackPHI = IRB.CreatePHI(Ty: PtrTy, NumReservedValues: 2, Name: "ptr");
134 auto *CallBack = IRB.CreateLoad(Ty: F.getType(), Ptr: CallBackPHI, Name: "callback");
135 IRB.CreateCall(FTy: CallBackTy, Callee: CallBack);
136 auto *NewCallBack =
137 IRB.CreateConstGEP1_64(Ty: PtrTy, Ptr: CallBackPHI, Idx0: IsCtor ? 1 : -1, Name: "next");
138 auto *EndCmp = IRB.CreateCmp(Pred: IsCtor ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_ULT,
139 LHS: NewCallBack, RHS: Stop, Name: "end");
140 CallBackPHI->addIncoming(V: Start, BB: &F.getEntryBlock());
141 CallBackPHI->addIncoming(V: NewCallBack, BB: LoopBB);
142 IRB.CreateCondBr(Cond: EndCmp, True: ExitBB, False: LoopBB);
143 IRB.SetInsertPoint(ExitBB);
144 IRB.CreateRetVoid();
145}
146
147static bool createInitOrFiniKernel(Module &M, StringRef GlobalName,
148 bool IsCtor) {
149 GlobalVariable *GV = M.getGlobalVariable(Name: GlobalName);
150 if (!GV || !GV->hasInitializer())
151 return false;
152 ConstantArray *GA = dyn_cast<ConstantArray>(Val: GV->getInitializer());
153 if (!GA || GA->getNumOperands() == 0)
154 return false;
155
156 Function *InitOrFiniKernel = createInitOrFiniKernelFunction(M, IsCtor);
157 if (!InitOrFiniKernel)
158 return false;
159
160 createInitOrFiniCalls(F&: *InitOrFiniKernel, IsCtor);
161
162 appendToUsed(M, Values: {InitOrFiniKernel});
163 return true;
164}
165
166static bool lowerCtorsAndDtors(Module &M) {
167 bool Modified = false;
168 Modified |= createInitOrFiniKernel(M, GlobalName: "llvm.global_ctors", /*IsCtor =*/true);
169 Modified |= createInitOrFiniKernel(M, GlobalName: "llvm.global_dtors", /*IsCtor =*/false);
170 return Modified;
171}
172
173class AMDGPUCtorDtorLoweringLegacy final : public ModulePass {
174public:
175 static char ID;
176 AMDGPUCtorDtorLoweringLegacy() : ModulePass(ID) {}
177 bool runOnModule(Module &M) override { return lowerCtorsAndDtors(M); }
178};
179
180} // End anonymous namespace
181
182PreservedAnalyses AMDGPUCtorDtorLoweringPass::run(Module &M,
183 ModuleAnalysisManager &AM) {
184 return lowerCtorsAndDtors(M) ? PreservedAnalyses::none()
185 : PreservedAnalyses::all();
186}
187
188char AMDGPUCtorDtorLoweringLegacy::ID = 0;
189char &llvm::AMDGPUCtorDtorLoweringLegacyPassID =
190 AMDGPUCtorDtorLoweringLegacy::ID;
191INITIALIZE_PASS(AMDGPUCtorDtorLoweringLegacy, DEBUG_TYPE,
192 "Lower ctors and dtors for AMDGPU", false, false)
193
194ModulePass *llvm::createAMDGPUCtorDtorLoweringLegacyPass() {
195 return new AMDGPUCtorDtorLoweringLegacy();
196}
197