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 //
57 // using InitCallback = void();
58 //
59 // void call_init_array_callbacks() {
60 //   for (auto start = __init_array_start; start != __init_array_end; ++start)
61 //     reinterpret_cast<InitCallback *>(*start)();
62 // }
63 static void createInitOrFiniCalls(Function &F, bool IsCtor) {
64   Module &M = *F.getParent();
65   LLVMContext &C = M.getContext();
66 
67   IRBuilder<> IRB(BasicBlock::Create(C, "entry", &F));
68   auto *LoopBB = BasicBlock::Create(C, "while.entry", &F);
69   auto *ExitBB = BasicBlock::Create(C, "while.end", &F);
70   Type *PtrTy = IRB.getPtrTy(AMDGPUAS::GLOBAL_ADDRESS);
71 
72   auto *Begin = M.getOrInsertGlobal(
73       IsCtor ? "__init_array_start" : "__fini_array_start",
74       ArrayType::get(PtrTy, 0), [&]() {
75         return new GlobalVariable(
76             M, ArrayType::get(PtrTy, 0),
77             /*isConstant=*/true, GlobalValue::ExternalLinkage,
78             /*Initializer=*/nullptr,
79             IsCtor ? "__init_array_start" : "__fini_array_start",
80             /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
81             /*AddressSpace=*/1);
82       });
83   auto *End = M.getOrInsertGlobal(
84       IsCtor ? "__init_array_end" : "__fini_array_end",
85       ArrayType::get(PtrTy, 0), [&]() {
86         return new GlobalVariable(
87             M, ArrayType::get(PtrTy, 0),
88             /*isConstant=*/true, GlobalValue::ExternalLinkage,
89             /*Initializer=*/nullptr,
90             IsCtor ? "__init_array_end" : "__fini_array_end",
91             /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
92             /*AddressSpace=*/1);
93       });
94 
95   // The constructor type is suppoed to allow using the argument vectors, but
96   // for now we just call them with no arguments.
97   auto *CallBackTy = FunctionType::get(IRB.getVoidTy(), {});
98 
99   IRB.CreateCondBr(IRB.CreateICmpNE(Begin, End), LoopBB, ExitBB);
100   IRB.SetInsertPoint(LoopBB);
101   auto *CallBackPHI = IRB.CreatePHI(PtrTy, 2, "ptr");
102   auto *CallBack = IRB.CreateLoad(CallBackTy->getPointerTo(F.getAddressSpace()),
103                                   CallBackPHI, "callback");
104   IRB.CreateCall(CallBackTy, CallBack);
105   auto *NewCallBack = IRB.CreateConstGEP1_64(PtrTy, CallBackPHI, 1, "next");
106   auto *EndCmp = IRB.CreateICmpEQ(NewCallBack, End, "end");
107   CallBackPHI->addIncoming(Begin, &F.getEntryBlock());
108   CallBackPHI->addIncoming(NewCallBack, LoopBB);
109   IRB.CreateCondBr(EndCmp, ExitBB, LoopBB);
110   IRB.SetInsertPoint(ExitBB);
111   IRB.CreateRetVoid();
112 }
113 
114 static bool createInitOrFiniKernel(Module &M, StringRef GlobalName,
115                                    bool IsCtor) {
116   GlobalVariable *GV = M.getGlobalVariable(GlobalName);
117   if (!GV || !GV->hasInitializer())
118     return false;
119   ConstantArray *GA = dyn_cast<ConstantArray>(GV->getInitializer());
120   if (!GA || GA->getNumOperands() == 0)
121     return false;
122 
123   Function *InitOrFiniKernel = createInitOrFiniKernelFunction(M, IsCtor);
124   if (!InitOrFiniKernel)
125     return false;
126 
127   createInitOrFiniCalls(*InitOrFiniKernel, IsCtor);
128 
129   appendToUsed(M, {InitOrFiniKernel});
130   return true;
131 }
132 
133 static bool lowerCtorsAndDtors(Module &M) {
134   bool Modified = false;
135   Modified |= createInitOrFiniKernel(M, "llvm.global_ctors", /*IsCtor =*/true);
136   Modified |= createInitOrFiniKernel(M, "llvm.global_dtors", /*IsCtor =*/false);
137   return Modified;
138 }
139 
140 class AMDGPUCtorDtorLoweringLegacy final : public ModulePass {
141 public:
142   static char ID;
143   AMDGPUCtorDtorLoweringLegacy() : ModulePass(ID) {}
144   bool runOnModule(Module &M) override { return lowerCtorsAndDtors(M); }
145 };
146 
147 } // End anonymous namespace
148 
149 PreservedAnalyses AMDGPUCtorDtorLoweringPass::run(Module &M,
150                                                   ModuleAnalysisManager &AM) {
151   return lowerCtorsAndDtors(M) ? PreservedAnalyses::none()
152                                : PreservedAnalyses::all();
153 }
154 
155 char AMDGPUCtorDtorLoweringLegacy::ID = 0;
156 char &llvm::AMDGPUCtorDtorLoweringLegacyPassID =
157     AMDGPUCtorDtorLoweringLegacy::ID;
158 INITIALIZE_PASS(AMDGPUCtorDtorLoweringLegacy, DEBUG_TYPE,
159                 "Lower ctors and dtors for AMDGPU", false, false)
160 
161 ModulePass *llvm::createAMDGPUCtorDtorLoweringLegacyPass() {
162   return new AMDGPUCtorDtorLoweringLegacy();
163 }
164