llvm/lib/Target/NVPTX/NVPTXCtorDtorLowering.cpp

   1 //===-- NVPTXCtorDtorLowering.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 "NVPTXCtorDtorLowering.h"
  14 #include "MCTargetDesc/NVPTXBaseInfo.h"
  15 #include "NVPTX.h"
  16 #include "llvm/ADT/StringExtras.h"
  17 #include "llvm/IR/Constants.h"
  18 #include "llvm/IR/Function.h"
  19 #include "llvm/IR/GlobalVariable.h"
  20 #include "llvm/IR/IRBuilder.h"
  21 #include "llvm/IR/Module.h"
  22 #include "llvm/IR/Value.h"
  23 #include "llvm/Pass.h"
  24 #include "llvm/Support/CommandLine.h"
  25 #include "llvm/Transforms/Utils/ModuleUtils.h"
  26
  27 using namespace llvm;
  28
  29 #define DEBUG_TYPE "nvptx-lower-ctor-dtor"
  30
  31 static cl::opt<std::string>
  32     GlobalStr("nvptx-lower-global-ctor-dtor-id",
  33               cl::desc("Override unique ID of ctor/dtor globals."),
  34               cl::init(""), cl::Hidden);
  35
  36 static cl::opt<bool>
  37     CreateKernels("nvptx-emit-init-fini-kernel",
  38                   cl::desc("Emit kernels to call ctor/dtor globals."),
  39                   cl::init(true), cl::Hidden);
  40
  41 namespace {
  42
  43 static std::string getHash(StringRef Str) {
  44   llvm::MD5 Hasher;
  45   llvm::MD5::MD5Result Hash;
  46   Hasher.update(Str);
  47   Hasher.final(Hash);
  48   return llvm::utohexstr(Hash.low(), /*LowerCase=*/true);
  49 }
  50
  51 static void addKernelMetadata(Module &M, GlobalValue *GV) {
  52   llvm::LLVMContext &Ctx = M.getContext();
  53
  54   // Get "nvvm.annotations" metadata node.
  55   llvm::NamedMDNode *MD = M.getOrInsertNamedMetadata("nvvm.annotations");
  56
  57   llvm::Metadata *KernelMDVals[] = {
  58       llvm::ConstantAsMetadata::get(GV), llvm::MDString::get(Ctx, "kernel"),
  59       llvm::ConstantAsMetadata::get(
  60           llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))};
  61
  62   // This kernel is only to be called single-threaded.
  63   llvm::Metadata *ThreadXMDVals[] = {
  64       llvm::ConstantAsMetadata::get(GV), llvm::MDString::get(Ctx, "maxntidx"),
  65       llvm::ConstantAsMetadata::get(
  66           llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))};
  67   llvm::Metadata *ThreadYMDVals[] = {
  68       llvm::ConstantAsMetadata::get(GV), llvm::MDString::get(Ctx, "maxntidy"),
  69       llvm::ConstantAsMetadata::get(
  70           llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))};
  71   llvm::Metadata *ThreadZMDVals[] = {
  72       llvm::ConstantAsMetadata::get(GV), llvm::MDString::get(Ctx, "maxntidz"),
  73       llvm::ConstantAsMetadata::get(
  74           llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))};
  75
  76   llvm::Metadata *BlockMDVals[] = {
  77       llvm::ConstantAsMetadata::get(GV),
  78       llvm::MDString::get(Ctx, "maxclusterrank"),
  79       llvm::ConstantAsMetadata::get(
  80           llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))};
  81
  82   // Append metadata to nvvm.annotations.
  83   MD->addOperand(llvm::MDNode::get(Ctx, KernelMDVals));
  84   MD->addOperand(llvm::MDNode::get(Ctx, ThreadXMDVals));
  85   MD->addOperand(llvm::MDNode::get(Ctx, ThreadYMDVals));
  86   MD->addOperand(llvm::MDNode::get(Ctx, ThreadZMDVals));
  87   MD->addOperand(llvm::MDNode::get(Ctx, BlockMDVals));
  88 }
  89
  90 static Function *createInitOrFiniKernelFunction(Module &M, bool IsCtor) {
  91   StringRef InitOrFiniKernelName =
  92       IsCtor ? "nvptx$device$init" : "nvptx$device$fini";
  93   if (M.getFunction(InitOrFiniKernelName))
  94     return nullptr;
  95
  96   Function *InitOrFiniKernel = Function::createWithDefaultAttr(
  97       FunctionType::get(Type::getVoidTy(M.getContext()), false),
  98       GlobalValue::WeakODRLinkage, 0, InitOrFiniKernelName, &M);
  99   addKernelMetadata(M, InitOrFiniKernel);
 100
 101   return InitOrFiniKernel;
 102 }
 103
 104 // We create the IR required to call each callback in this section. This is
 105 // equivalent to the following code. Normally, the linker would provide us with
 106 // the definitions of the init and fini array sections. The 'nvlink' linker does
 107 // not do this so initializing these values is done by the runtime.
 108 //
 109 // extern "C" void **__init_array_start = nullptr;
 110 // extern "C" void **__init_array_end = nullptr;
 111 // extern "C" void **__fini_array_start = nullptr;
 112 // extern "C" void **__fini_array_end = nullptr;
 113 //
 114 // using InitCallback = void();
 115 // using FiniCallback = void();
 116 //
 117 // void call_init_array_callbacks() {
 118 //   for (auto start = __init_array_start; start != __init_array_end; ++start)
 119 //     reinterpret_cast<InitCallback *>(*start)();
 120 // }
 121 //
 122 // void call_init_array_callbacks() {
 123 //   size_t fini_array_size = __fini_array_end - __fini_array_start;
 124 //   for (size_t i = fini_array_size; i > 0; --i)
 125 //     reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
 126 // }
 127 static void createInitOrFiniCalls(Function &F, bool IsCtor) {
 128   Module &M = *F.getParent();
 129   LLVMContext &C = M.getContext();
 130
 131   IRBuilder<> IRB(BasicBlock::Create(C, "entry", &F));
 132   auto *LoopBB = BasicBlock::Create(C, "while.entry", &F);
 133   auto *ExitBB = BasicBlock::Create(C, "while.end", &F);
 134   Type *PtrTy = IRB.getPtrTy(llvm::ADDRESS_SPACE_GLOBAL);
 135
 136   auto *Begin = M.getOrInsertGlobal(
 137       IsCtor ? "__init_array_start" : "__fini_array_start",
 138       PointerType::get(C, 0), [&]() {
 139         auto *GV = new GlobalVariable(
 140             M, PointerType::get(C, 0),
 141             /*isConstant=*/false, GlobalValue::WeakAnyLinkage,
 142             Constant::getNullValue(PointerType::get(C, 0)),
 143             IsCtor ? "__init_array_start" : "__fini_array_start",
 144             /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
 145             /*AddressSpace=*/llvm::ADDRESS_SPACE_GLOBAL);
 146         GV->setVisibility(GlobalVariable::ProtectedVisibility);
 147         return GV;
 148       });
 149   auto *End = M.getOrInsertGlobal(
 150       IsCtor ? "__init_array_end" : "__fini_array_end", PointerType::get(C, 0),
 151       [&]() {
 152         auto *GV = new GlobalVariable(
 153             M, PointerType::get(C, 0),
 154             /*isConstant=*/false, GlobalValue::WeakAnyLinkage,
 155             Constant::getNullValue(PointerType::get(C, 0)),
 156             IsCtor ? "__init_array_end" : "__fini_array_end",
 157             /*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
 158             /*AddressSpace=*/llvm::ADDRESS_SPACE_GLOBAL);
 159         GV->setVisibility(GlobalVariable::ProtectedVisibility);
 160         return GV;
 161       });
 162
 163   // The constructor type is suppoed to allow using the argument vectors, but
 164   // for now we just call them with no arguments.
 165   auto *CallBackTy = FunctionType::get(IRB.getVoidTy(), {});
 166
 167   // The destructor array must be called in reverse order. Get an expression to
 168   // the end of the array and iterate backwards in that case.
 169   Value *BeginVal = IRB.CreateLoad(Begin->getType(), Begin, "begin");
 170   Value *EndVal = IRB.CreateLoad(Begin->getType(), End, "stop");
 171   if (!IsCtor) {
 172     auto *BeginInt = IRB.CreatePtrToInt(BeginVal, IntegerType::getInt64Ty(C));
 173     auto *EndInt = IRB.CreatePtrToInt(EndVal, IntegerType::getInt64Ty(C));
 174     auto *SubInst = IRB.CreateSub(EndInt, BeginInt);
 175     auto *Offset = IRB.CreateAShr(
 176         SubInst, ConstantInt::get(IntegerType::getInt64Ty(C), 3), "offset",
 177         /*IsExact=*/true);
 178     auto *ValuePtr = IRB.CreateGEP(PointerType::get(C, 0), BeginVal,
 179                                    ArrayRef<Value *>({Offset}));
 180     EndVal = BeginVal;
 181     BeginVal = IRB.CreateInBoundsGEP(
 182         PointerType::get(C, 0), ValuePtr,
 183         ArrayRef<Value *>(ConstantInt::get(IntegerType::getInt64Ty(C), -1)),
 184         "start");
 185   }
 186   IRB.CreateCondBr(
 187       IRB.CreateCmp(IsCtor ? ICmpInst::ICMP_NE : ICmpInst::ICMP_UGT, BeginVal,
 188                     EndVal),
 189       LoopBB, ExitBB);
 190   IRB.SetInsertPoint(LoopBB);
 191   auto *CallBackPHI = IRB.CreatePHI(PtrTy, 2, "ptr");
 192   auto *CallBack = IRB.CreateLoad(IRB.getPtrTy(F.getAddressSpace()),
 193                                   CallBackPHI, "callback");
 194   IRB.CreateCall(CallBackTy, CallBack);
 195   auto *NewCallBack =
 196       IRB.CreateConstGEP1_64(PtrTy, CallBackPHI, IsCtor ? 1 : -1, "next");
 197   auto *EndCmp = IRB.CreateCmp(IsCtor ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_ULT,
 198                                NewCallBack, EndVal, "end");
 199   CallBackPHI->addIncoming(BeginVal, &F.getEntryBlock());
 200   CallBackPHI->addIncoming(NewCallBack, LoopBB);
 201   IRB.CreateCondBr(EndCmp, ExitBB, LoopBB);
 202   IRB.SetInsertPoint(ExitBB);
 203   IRB.CreateRetVoid();
 204 }
 205
 206 static bool createInitOrFiniGlobals(Module &M, GlobalVariable *GV,
 207                                     bool IsCtor) {
 208   ConstantArray *GA = dyn_cast<ConstantArray>(GV->getInitializer());
 209   if (!GA || GA->getNumOperands() == 0)
 210     return false;
 211
 212   // NVPTX has no way to emit variables at specific sections or support for
 213   // the traditional constructor sections. Instead, we emit mangled global
 214   // names so the runtime can build the list manually.
 215   for (Value *V : GA->operands()) {
 216     auto *CS = cast<ConstantStruct>(V);
 217     auto *F = cast<Constant>(CS->getOperand(1));
 218     uint64_t Priority = cast<ConstantInt>(CS->getOperand(0))->getSExtValue();
 219     std::string PriorityStr = "." + std::to_string(Priority);
 220     // We append a semi-unique hash and the priority to the global name.
 221     std::string GlobalID =
 222         !GlobalStr.empty() ? GlobalStr : getHash(M.getSourceFileName());
 223     std::string NameStr =
 224         ((IsCtor ? "__init_array_object_" : "__fini_array_object_") +
 225          F->getName() + "_" + GlobalID + "_" + std::to_string(Priority))
 226             .str();
 227     // PTX does not support exported names with '.' in them.
 228     llvm::transform(NameStr, NameStr.begin(),
 229                     [](char c) { return c == '.' ? '_' : c; });
 230
 231     auto *GV = new GlobalVariable(M, F->getType(), /*IsConstant=*/true,
 232                                   GlobalValue::ExternalLinkage, F, NameStr,
 233                                   nullptr, GlobalValue::NotThreadLocal,
 234                                   /*AddressSpace=*/4);
 235     // This isn't respected by Nvidia, simply put here for clarity.
 236     GV->setSection(IsCtor ? ".init_array" + PriorityStr
 237                           : ".fini_array" + PriorityStr);
 238     GV->setVisibility(GlobalVariable::ProtectedVisibility);
 239     appendToUsed(M, {GV});
 240   }
 241
 242   return true;
 243 }
 244
 245 static bool createInitOrFiniKernel(Module &M, StringRef GlobalName,
 246                                    bool IsCtor) {
 247   GlobalVariable *GV = M.getGlobalVariable(GlobalName);
 248   if (!GV || !GV->hasInitializer())
 249     return false;
 250
 251   if (!createInitOrFiniGlobals(M, GV, IsCtor))
 252     return false;
 253
 254   if (!CreateKernels)
 255     return true;
 256
 257   Function *InitOrFiniKernel = createInitOrFiniKernelFunction(M, IsCtor);
 258   if (!InitOrFiniKernel)
 259     return false;
 260
 261   createInitOrFiniCalls(*InitOrFiniKernel, IsCtor);
 262
 263   GV->eraseFromParent();
 264   return true;
 265 }
 266
 267 static bool lowerCtorsAndDtors(Module &M) {
 268   bool Modified = false;
 269   Modified |= createInitOrFiniKernel(M, "llvm.global_ctors", /*IsCtor =*/true);
 270   Modified |= createInitOrFiniKernel(M, "llvm.global_dtors", /*IsCtor =*/false);
 271   return Modified;
 272 }
 273
 274 class NVPTXCtorDtorLoweringLegacy final : public ModulePass {
 275 public:
 276   static char ID;
 277   NVPTXCtorDtorLoweringLegacy() : ModulePass(ID) {}
 278   bool runOnModule(Module &M) override { return lowerCtorsAndDtors(M); }
 279 };
 280
 281 } // End anonymous namespace
 282
 283 PreservedAnalyses NVPTXCtorDtorLoweringPass::run(Module &M,
 284                                                  ModuleAnalysisManager &AM) {
 285   return lowerCtorsAndDtors(M) ? PreservedAnalyses::none()
 286                                : PreservedAnalyses::all();
 287 }
 288
 289 char NVPTXCtorDtorLoweringLegacy::ID = 0;
 290 char &llvm::NVPTXCtorDtorLoweringLegacyPassID = NVPTXCtorDtorLoweringLegacy::ID;
 291 INITIALIZE_PASS(NVPTXCtorDtorLoweringLegacy, DEBUG_TYPE,
 292                 "Lower ctors and dtors for NVPTX", false, false)
 293
 294 ModulePass *llvm::createNVPTXCtorDtorLoweringLegacyPass() {
 295   return new NVPTXCtorDtorLoweringLegacy();
 296 }