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 "MCTargetDesc/SPIRVBaseInfo.h"
15#include "SPIRV.h"
16#include "llvm/ADT/STLFunctionalExtras.h"
17#include "llvm/ADT/StringExtras.h"
18#include "llvm/IR/CallingConv.h"
19#include "llvm/IR/Constants.h"
20#include "llvm/IR/Function.h"
21#include "llvm/IR/GlobalVariable.h"
22#include "llvm/IR/IRBuilder.h"
23#include "llvm/IR/Module.h"
24#include "llvm/IR/Value.h"
25#include "llvm/Pass.h"
26#include "llvm/Support/CommandLine.h"
27#include "llvm/Support/MD5.h"
28#include "llvm/Transforms/IPO/OpenMPOpt.h"
29#include "llvm/Transforms/Utils/ModuleUtils.h"
30
31using namespace llvm;
32
33#define DEBUG_TYPE "spirv-lower-ctor-dtor"
34
35static cl::opt<std::string>
36 GlobalStr("spirv-lower-global-ctor-dtor-id",
37 cl::desc("Override unique ID of ctor/dtor globals."),
38 cl::init(Val: ""), cl::Hidden);
39
40static cl::opt<bool>
41 CreateKernels("spirv-emit-init-fini-kernel",
42 cl::desc("Emit kernels to call ctor/dtor globals."),
43 cl::init(Val: true), cl::Hidden);
44
45namespace {
46constexpr int SPIRV_GLOBAL_AS = 1;
47
48std::string getHash(StringRef Str) {
49 llvm::MD5 Hasher;
50 llvm::MD5::MD5Result Hash;
51 Hasher.update(Str);
52 Hasher.final(Result&: Hash);
53 return llvm::utohexstr(X: Hash.low(), /*LowerCase=*/true);
54}
55
56void addKernelAttrs(Function *F) {
57 F->setCallingConv(CallingConv::SPIR_KERNEL);
58 F->addFnAttr(Kind: "uniform-work-group-size", Val: "true");
59}
60
61Function *createInitOrFiniKernelFunction(Module &M, bool IsCtor) {
62 StringRef InitOrFiniKernelName =
63 IsCtor ? "spirv$device$init" : "spirv$device$fini";
64 if (M.getFunction(Name: InitOrFiniKernelName))
65 return nullptr;
66
67 Function *InitOrFiniKernel = Function::createWithDefaultAttr(
68 Ty: FunctionType::get(Result: Type::getVoidTy(C&: M.getContext()), isVarArg: false),
69 Linkage: GlobalValue::WeakODRLinkage, AddrSpace: 0, N: InitOrFiniKernelName, M: &M);
70 addKernelAttrs(F: InitOrFiniKernel);
71
72 return InitOrFiniKernel;
73}
74
75// We create the IR required to call each callback in this section. This is
76// equivalent to the following code. Normally, the linker would provide us with
77// the definitions of the init and fini array sections. The 'spirv-link' linker
78// does not do this so initializing these values is done by the offload runtime.
79//
80// extern "C" void **__init_array_start = nullptr;
81// extern "C" void **__init_array_end = nullptr;
82// extern "C" void **__fini_array_start = nullptr;
83// extern "C" void **__fini_array_end = nullptr;
84//
85// using InitCallback = void();
86// using FiniCallback = void();
87//
88// void call_init_array_callbacks() {
89// for (auto start = __init_array_start; start != __init_array_end; ++start)
90// reinterpret_cast<InitCallback *>(*start)();
91// }
92//
93// void call_fini_array_callbacks() {
94// size_t fini_array_size = __fini_array_end - __fini_array_start;
95// for (size_t i = fini_array_size; i > 0; --i)
96// reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
97// }
98void createInitOrFiniCalls(Function &F, bool IsCtor) {
99 Module &M = *F.getParent();
100 LLVMContext &C = M.getContext();
101
102 IRBuilder<> IRB(BasicBlock::Create(Context&: C, Name: "entry", Parent: &F));
103 auto *LoopBB = BasicBlock::Create(Context&: C, Name: "while.entry", Parent: &F);
104 auto *ExitBB = BasicBlock::Create(Context&: C, Name: "while.end", Parent: &F);
105 Type *PtrTy = IRB.getPtrTy(AddrSpace: SPIRV_GLOBAL_AS);
106
107 auto CreateGlobal = [&](const char *Name) -> GlobalVariable * {
108 auto *GV = new GlobalVariable(
109 M, PointerType::getUnqual(C),
110 /*isConstant=*/false, GlobalValue::WeakAnyLinkage,
111 Constant::getNullValue(Ty: PointerType::getUnqual(C)), Name,
112 /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
113 /*AddressSpace=*/SPIRV_GLOBAL_AS);
114 GV->setVisibility(GlobalVariable::ProtectedVisibility);
115 return GV;
116 };
117
118 auto *Begin = M.getOrInsertGlobal(
119 Name: IsCtor ? "__init_array_start" : "__fini_array_start",
120 Ty: PointerType::getUnqual(C), CreateGlobalCallback: function_ref<GlobalVariable *()>([&]() {
121 return CreateGlobal(IsCtor ? "__init_array_start"
122 : "__fini_array_start");
123 }));
124 auto *End = M.getOrInsertGlobal(
125 Name: IsCtor ? "__init_array_end" : "__fini_array_end",
126 Ty: PointerType::getUnqual(C), CreateGlobalCallback: function_ref<GlobalVariable *()>([&]() {
127 return CreateGlobal(IsCtor ? "__init_array_end" : "__fini_array_end");
128 }));
129 auto *CallBackTy = FunctionType::get(Result: IRB.getVoidTy(), isVarArg: {});
130
131 // The destructor array must be called in reverse order. Get an expression to
132 // the end of the array and iterate backwards in that case.
133 Value *BeginVal = IRB.CreateLoad(Ty: Begin->getType(), Ptr: Begin, Name: "begin");
134 Value *EndVal = IRB.CreateLoad(Ty: Begin->getType(), Ptr: End, Name: "stop");
135 if (!IsCtor) {
136 Value *OldBeginVal = BeginVal;
137 BeginVal =
138 IRB.CreateInBoundsGEP(Ty: PointerType::getUnqual(C), Ptr: EndVal,
139 IdxList: ArrayRef<Value *>(ConstantInt::getAllOnesValue(
140 Ty: IntegerType::getInt64Ty(C))),
141 Name: "start");
142 EndVal = OldBeginVal;
143 }
144 IRB.CreateCondBr(
145 Cond: IRB.CreateCmp(Pred: IsCtor ? ICmpInst::ICMP_NE : ICmpInst::ICMP_UGE, LHS: BeginVal,
146 RHS: EndVal),
147 True: LoopBB, False: ExitBB);
148 IRB.SetInsertPoint(LoopBB);
149 auto *CallBackPHI = IRB.CreatePHI(Ty: PtrTy, NumReservedValues: 2, Name: "ptr");
150 auto *CallBack = IRB.CreateLoad(Ty: IRB.getPtrTy(AddrSpace: F.getAddressSpace()),
151 Ptr: CallBackPHI, Name: "callback");
152 IRB.CreateCall(FTy: CallBackTy, Callee: CallBack);
153 auto *NewCallBack =
154 IRB.CreateConstGEP1_64(Ty: PtrTy, Ptr: CallBackPHI, Idx0: IsCtor ? 1 : -1, Name: "next");
155 auto *EndCmp = IRB.CreateCmp(Pred: IsCtor ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_ULT,
156 LHS: NewCallBack, RHS: EndVal, Name: "end");
157 CallBackPHI->addIncoming(V: BeginVal, BB: &F.getEntryBlock());
158 CallBackPHI->addIncoming(V: NewCallBack, BB: LoopBB);
159 IRB.CreateCondBr(Cond: EndCmp, True: ExitBB, False: LoopBB);
160 IRB.SetInsertPoint(ExitBB);
161 IRB.CreateRetVoid();
162}
163
164bool createInitOrFiniGlobals(Module &M, GlobalVariable *GV, bool IsCtor) {
165 ConstantArray *GA = dyn_cast<ConstantArray>(Val: GV->getInitializer());
166 if (!GA || GA->getNumOperands() == 0)
167 return false;
168
169 // SPIR-V has no way to emit variables at specific sections or support for
170 // the traditional constructor sections. Instead, we emit mangled global
171 // names so the runtime can build the list manually.
172 for (Value *V : GA->operands()) {
173 auto *CS = cast<ConstantStruct>(Val: V);
174 auto *F = cast<Constant>(Val: CS->getOperand(i_nocapture: 1));
175 uint64_t Priority = cast<ConstantInt>(Val: CS->getOperand(i_nocapture: 0))->getSExtValue();
176 std::string PriorityStr = "." + std::to_string(val: Priority);
177 // We append a semi-unique hash and the priority to the global name.
178 std::string GlobalID =
179 !GlobalStr.empty() ? GlobalStr : getHash(Str: M.getSourceFileName());
180 std::string NameStr =
181 ((IsCtor ? "__init_array_object_" : "__fini_array_object_") +
182 F->getName() + "_" + GlobalID + "_" + std::to_string(val: Priority))
183 .str();
184 llvm::transform(Range&: NameStr, d_first: NameStr.begin(),
185 F: [](char c) { return c == '.' ? '_' : c; });
186
187 auto *GV = new GlobalVariable(M, F->getType(), /*IsConstant=*/true,
188 GlobalValue::ExternalLinkage, F, NameStr,
189 nullptr, GlobalValue::NotThreadLocal,
190 /*AddressSpace=*/SPIRV_GLOBAL_AS);
191 GV->setSection(IsCtor ? ".init_array" + PriorityStr
192 : ".fini_array" + PriorityStr);
193 GV->setVisibility(GlobalVariable::ProtectedVisibility);
194 }
195
196 return true;
197}
198
199bool createInitOrFiniKernel(Module &M, StringRef GlobalName, bool IsCtor) {
200 GlobalVariable *GV = M.getGlobalVariable(Name: GlobalName);
201 if (!GV || !GV->hasInitializer())
202 return false;
203
204 if (!createInitOrFiniGlobals(M, GV, IsCtor))
205 return false;
206
207 if (!CreateKernels)
208 return true;
209
210 Function *InitOrFiniKernel = createInitOrFiniKernelFunction(M, IsCtor);
211 if (!InitOrFiniKernel)
212 return false;
213
214 createInitOrFiniCalls(F&: *InitOrFiniKernel, IsCtor);
215
216 GV->eraseFromParent();
217 return true;
218}
219
220bool lowerCtorsAndDtors(Module &M) {
221 // Only run this pass for OpenMP offload compilation
222 if (!llvm::omp::isOpenMPDevice(M))
223 return false;
224
225 bool Modified = false;
226 Modified |= createInitOrFiniKernel(M, GlobalName: "llvm.global_ctors", /*IsCtor =*/true);
227 Modified |= createInitOrFiniKernel(M, GlobalName: "llvm.global_dtors", /*IsCtor =*/false);
228 return Modified;
229}
230
231class SPIRVCtorDtorLoweringLegacy final : public ModulePass {
232public:
233 static char ID;
234 SPIRVCtorDtorLoweringLegacy() : ModulePass(ID) {}
235 bool runOnModule(Module &M) override { return lowerCtorsAndDtors(M); }
236};
237
238} // End anonymous namespace
239
240PreservedAnalyses SPIRVCtorDtorLoweringPass::run(Module &M,
241 ModuleAnalysisManager &AM) {
242 return lowerCtorsAndDtors(M) ? PreservedAnalyses::none()
243 : PreservedAnalyses::all();
244}
245
246char SPIRVCtorDtorLoweringLegacy::ID = 0;
247INITIALIZE_PASS(SPIRVCtorDtorLoweringLegacy, DEBUG_TYPE,
248 "SPIRV lower ctors and dtors", false, false)
249
250ModulePass *llvm::createSPIRVCtorDtorLoweringLegacyPass() {
251 return new SPIRVCtorDtorLoweringLegacy();
252}
253