1//===-- SPIRVCtorDtorLowering.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// This pass creates a unified init and fini kernel with the required metadata
10// to call global constructors and destructors on SPIR-V targets.
11//
12//===----------------------------------------------------------------------===//
13
14#include "SPIRV.h"
15#include "llvm/ADT/STLFunctionalExtras.h"
16#include "llvm/ADT/StringExtras.h"
17#include "llvm/IR/CallingConv.h"
18#include "llvm/IR/Constants.h"
19#include "llvm/IR/Function.h"
20#include "llvm/IR/GlobalVariable.h"
21#include "llvm/IR/IRBuilder.h"
22#include "llvm/IR/Module.h"
23#include "llvm/IR/Value.h"
24#include "llvm/Pass.h"
25#include "llvm/Support/CommandLine.h"
26#include "llvm/Support/MD5.h"
27#include "llvm/Transforms/IPO/OpenMPOpt.h"
28#include "llvm/Transforms/Utils/ModuleUtils.h"
29
30using namespace llvm;
31
32#define DEBUG_TYPE "spirv-lower-ctor-dtor"
33
34static cl::opt<std::string>
35 GlobalStr("spirv-lower-global-ctor-dtor-id",
36 cl::desc("Override unique ID of ctor/dtor globals."),
37 cl::init(Val: ""), cl::Hidden);
38
39static cl::opt<bool>
40 CreateKernels("spirv-emit-init-fini-kernel",
41 cl::desc("Emit kernels to call ctor/dtor globals."),
42 cl::init(Val: true), cl::Hidden);
43
44namespace {
45constexpr int SPIRV_GLOBAL_AS = 1;
46
47std::string getHash(StringRef Str) {
48 llvm::MD5 Hasher;
49 llvm::MD5::MD5Result Hash;
50 Hasher.update(Str);
51 Hasher.final(Result&: Hash);
52 return llvm::utohexstr(X: Hash.low(), /*LowerCase=*/true);
53}
54
55void addKernelAttrs(Function *F) {
56 F->setCallingConv(CallingConv::SPIR_KERNEL);
57 F->addFnAttr(Kind: "uniform-work-group-size", Val: "true");
58}
59
60Function *createInitOrFiniKernelFunction(Module &M, bool IsCtor) {
61 StringRef InitOrFiniKernelName =
62 IsCtor ? "spirv$device$init" : "spirv$device$fini";
63 if (M.getFunction(Name: InitOrFiniKernelName))
64 return nullptr;
65
66 Function *InitOrFiniKernel = Function::createWithDefaultAttr(
67 Ty: FunctionType::get(Result: Type::getVoidTy(C&: M.getContext()), isVarArg: false),
68 Linkage: GlobalValue::WeakODRLinkage, AddrSpace: 0, N: InitOrFiniKernelName, M: &M);
69 addKernelAttrs(F: InitOrFiniKernel);
70
71 return InitOrFiniKernel;
72}
73
74// We create the IR required to call each callback in this section. This is
75// equivalent to the following code. Normally, the linker would provide us with
76// the definitions of the init and fini array sections. The 'spirv-link' linker
77// does not do this so initializing these values is done by the offload runtime.
78//
79// extern "C" void **__init_array_start = nullptr;
80// extern "C" void **__init_array_end = nullptr;
81// extern "C" void **__fini_array_start = nullptr;
82// extern "C" void **__fini_array_end = nullptr;
83//
84// using InitCallback = void();
85// using FiniCallback = void();
86//
87// void call_init_array_callbacks() {
88// for (auto start = __init_array_start; start != __init_array_end; ++start)
89// reinterpret_cast<InitCallback *>(*start)();
90// }
91//
92// void call_fini_array_callbacks() {
93// size_t fini_array_size = __fini_array_end - __fini_array_start;
94// for (size_t i = fini_array_size; i > 0; --i)
95// reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
96// }
97void createInitOrFiniCalls(Function &F, bool IsCtor) {
98 Module &M = *F.getParent();
99 LLVMContext &C = M.getContext();
100
101 IRBuilder<> IRB(BasicBlock::Create(Context&: C, Name: "entry", Parent: &F));
102 auto *LoopBB = BasicBlock::Create(Context&: C, Name: "while.entry", Parent: &F);
103 auto *ExitBB = BasicBlock::Create(Context&: C, Name: "while.end", Parent: &F);
104 Type *PtrTy = IRB.getPtrTy(AddrSpace: SPIRV_GLOBAL_AS);
105
106 auto CreateGlobal = [&](const char *Name) -> GlobalVariable * {
107 auto *GV = new GlobalVariable(
108 M, PointerType::getUnqual(C),
109 /*isConstant=*/false, GlobalValue::WeakAnyLinkage,
110 Constant::getNullValue(Ty: PointerType::getUnqual(C)), Name,
111 /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
112 /*AddressSpace=*/SPIRV_GLOBAL_AS);
113 GV->setVisibility(GlobalVariable::ProtectedVisibility);
114 return GV;
115 };
116
117 auto *Begin = M.getOrInsertGlobal(
118 Name: IsCtor ? "__init_array_start" : "__fini_array_start",
119 Ty: PointerType::getUnqual(C), CreateGlobalCallback: function_ref<GlobalVariable *()>([&]() {
120 return CreateGlobal(IsCtor ? "__init_array_start"
121 : "__fini_array_start");
122 }));
123 auto *End = M.getOrInsertGlobal(
124 Name: IsCtor ? "__init_array_end" : "__fini_array_end",
125 Ty: PointerType::getUnqual(C), CreateGlobalCallback: function_ref<GlobalVariable *()>([&]() {
126 return CreateGlobal(IsCtor ? "__init_array_end" : "__fini_array_end");
127 }));
128 auto *CallBackTy = FunctionType::get(Result: IRB.getVoidTy(), isVarArg: {});
129
130 // The destructor array must be called in reverse order. Get an expression to
131 // the end of the array and iterate backwards in that case.
132 Value *BeginVal = IRB.CreateLoad(Ty: Begin->getType(), Ptr: Begin, Name: "begin");
133 Value *EndVal = IRB.CreateLoad(Ty: Begin->getType(), Ptr: End, Name: "stop");
134 if (!IsCtor) {
135 Value *OldBeginVal = BeginVal;
136 BeginVal =
137 IRB.CreateInBoundsGEP(Ty: PointerType::getUnqual(C), Ptr: EndVal,
138 IdxList: ArrayRef<Value *>(ConstantInt::getAllOnesValue(
139 Ty: IntegerType::getInt64Ty(C))),
140 Name: "start");
141 EndVal = OldBeginVal;
142 }
143 IRB.CreateCondBr(
144 Cond: IRB.CreateCmp(Pred: IsCtor ? ICmpInst::ICMP_NE : ICmpInst::ICMP_UGE, LHS: BeginVal,
145 RHS: EndVal),
146 True: LoopBB, False: ExitBB);
147 IRB.SetInsertPoint(LoopBB);
148 auto *CallBackPHI = IRB.CreatePHI(Ty: PtrTy, NumReservedValues: 2, Name: "ptr");
149 auto *CallBack = IRB.CreateLoad(Ty: IRB.getPtrTy(AddrSpace: F.getAddressSpace()),
150 Ptr: CallBackPHI, Name: "callback");
151 IRB.CreateCall(FTy: CallBackTy, Callee: CallBack);
152 auto *NewCallBack =
153 IRB.CreateConstGEP1_64(Ty: PtrTy, Ptr: CallBackPHI, Idx0: IsCtor ? 1 : -1, Name: "next");
154 auto *EndCmp = IRB.CreateCmp(Pred: IsCtor ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_ULT,
155 LHS: NewCallBack, RHS: EndVal, Name: "end");
156 CallBackPHI->addIncoming(V: BeginVal, BB: &F.getEntryBlock());
157 CallBackPHI->addIncoming(V: NewCallBack, BB: LoopBB);
158 IRB.CreateCondBr(Cond: EndCmp, True: ExitBB, False: LoopBB);
159 IRB.SetInsertPoint(ExitBB);
160 IRB.CreateRetVoid();
161}
162
163bool createInitOrFiniGlobals(Module &M, GlobalVariable *GV, bool IsCtor) {
164 ConstantArray *GA = dyn_cast<ConstantArray>(Val: GV->getInitializer());
165 if (!GA || GA->getNumOperands() == 0)
166 return false;
167
168 // SPIR-V has no way to emit variables at specific sections or support for
169 // the traditional constructor sections. Instead, we emit mangled global
170 // names so the runtime can build the list manually.
171 for (Value *V : GA->operands()) {
172 auto *CS = cast<ConstantStruct>(Val: V);
173 auto *F = cast<Constant>(Val: CS->getOperand(i_nocapture: 1));
174 uint64_t Priority = cast<ConstantInt>(Val: CS->getOperand(i_nocapture: 0))->getSExtValue();
175 std::string PriorityStr = "." + std::to_string(val: Priority);
176 // We append a semi-unique hash and the priority to the global name.
177 std::string GlobalID =
178 !GlobalStr.empty() ? GlobalStr : getHash(Str: M.getSourceFileName());
179 std::string NameStr =
180 ((IsCtor ? "__init_array_object_" : "__fini_array_object_") +
181 F->getName() + "_" + GlobalID + "_" + std::to_string(val: Priority))
182 .str();
183 llvm::transform(Range&: NameStr, d_first: NameStr.begin(),
184 F: [](char c) { return c == '.' ? '_' : c; });
185
186 auto *GV = new GlobalVariable(M, F->getType(), /*IsConstant=*/true,
187 GlobalValue::ExternalLinkage, F, NameStr,
188 nullptr, GlobalValue::NotThreadLocal,
189 /*AddressSpace=*/SPIRV_GLOBAL_AS);
190 GV->setSection(IsCtor ? ".init_array" + PriorityStr
191 : ".fini_array" + PriorityStr);
192 GV->setVisibility(GlobalVariable::ProtectedVisibility);
193 }
194
195 return true;
196}
197
198bool createInitOrFiniKernel(Module &M, StringRef GlobalName, bool IsCtor) {
199 GlobalVariable *GV = M.getGlobalVariable(Name: GlobalName);
200 if (!GV || !GV->hasInitializer())
201 return false;
202
203 if (!createInitOrFiniGlobals(M, GV, IsCtor))
204 return false;
205
206 if (!CreateKernels)
207 return true;
208
209 Function *InitOrFiniKernel = createInitOrFiniKernelFunction(M, IsCtor);
210 if (!InitOrFiniKernel)
211 return false;
212
213 createInitOrFiniCalls(F&: *InitOrFiniKernel, IsCtor);
214
215 GV->eraseFromParent();
216 return true;
217}
218
219bool lowerCtorsAndDtors(Module &M) {
220 // Only run this pass for OpenMP offload compilation
221 if (!llvm::omp::isOpenMPDevice(M))
222 return false;
223
224 bool Modified = false;
225 Modified |= createInitOrFiniKernel(M, GlobalName: "llvm.global_ctors", /*IsCtor =*/true);
226 Modified |= createInitOrFiniKernel(M, GlobalName: "llvm.global_dtors", /*IsCtor =*/false);
227 return Modified;
228}
229
230class SPIRVCtorDtorLoweringLegacy final : public ModulePass {
231public:
232 static char ID;
233 SPIRVCtorDtorLoweringLegacy() : ModulePass(ID) {}
234 bool runOnModule(Module &M) override { return lowerCtorsAndDtors(M); }
235};
236
237} // End anonymous namespace
238
239PreservedAnalyses SPIRVCtorDtorLoweringPass::run(Module &M,
240 ModuleAnalysisManager &AM) {
241 return lowerCtorsAndDtors(M) ? PreservedAnalyses::none()
242 : PreservedAnalyses::all();
243}
244
245char SPIRVCtorDtorLoweringLegacy::ID = 0;
246INITIALIZE_PASS(SPIRVCtorDtorLoweringLegacy, DEBUG_TYPE,
247 "SPIRV lower ctors and dtors", false, false)
248
249ModulePass *llvm::createSPIRVCtorDtorLoweringLegacyPass() {
250 return new SPIRVCtorDtorLoweringLegacy();
251}
252