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//===-- AMDGPUCtorDtorLowering.cpp - Handle global ctors and dtors --------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This pass creates a unified init and fini kernel with the required metadata
//===----------------------------------------------------------------------===//
#include "AMDGPUCtorDtorLowering.h"
#include "AMDGPU.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
using namespace llvm;
#define DEBUG_TYPE "amdgpu-lower-ctor-dtor"
namespace {
static Function *createInitOrFiniKernelFunction(Module &M, bool IsCtor) {
StringRef InitOrFiniKernelName = "amdgcn.device.init";
if (!IsCtor)
InitOrFiniKernelName = "amdgcn.device.fini";
if (M.getFunction(InitOrFiniKernelName))
return nullptr;
Function *InitOrFiniKernel = Function::createWithDefaultAttr(
FunctionType::get(Type::getVoidTy(M.getContext()), false),
GlobalValue::WeakODRLinkage, 0, InitOrFiniKernelName, &M);
InitOrFiniKernel->setCallingConv(CallingConv::AMDGPU_KERNEL);
InitOrFiniKernel->addFnAttr("amdgpu-flat-work-group-size", "1,1");
if (IsCtor)
InitOrFiniKernel->addFnAttr("device-init");
else
InitOrFiniKernel->addFnAttr("device-fini");
return InitOrFiniKernel;
}
// The linker will provide the associated symbols to allow us to traverse the
// global constructors / destructors in priority order. We create the IR
// required to call each callback in this section. This is equivalent to the
// following code.
//
// extern "C" void * __init_array_start[];
// extern "C" void * __init_array_end[];
// extern "C" void * __fini_array_start[];
// extern "C" void * __fini_array_end[];
//
// using InitCallback = void();
// using FiniCallback = void(void);
//
// void call_init_array_callbacks() {
// for (auto start = __init_array_start; start != __init_array_end; ++start)
// reinterpret_cast<InitCallback *>(*start)();
// }
//
// void call_fini_array_callbacks() {
// size_t fini_array_size = __fini_array_end - __fini_array_start;
// for (size_t i = fini_array_size; i > 0; --i)
// reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
// }
static void createInitOrFiniCalls(Function &F, bool IsCtor) {
Module &M = *F.getParent();
LLVMContext &C = M.getContext();
IRBuilder<> IRB(BasicBlock::Create(C, "entry", &F));
auto *LoopBB = BasicBlock::Create(C, "while.entry", &F);
auto *ExitBB = BasicBlock::Create(C, "while.end", &F);
Type *PtrTy = IRB.getPtrTy(AMDGPUAS::GLOBAL_ADDRESS);
auto *Begin = M.getOrInsertGlobal(
IsCtor ? "__init_array_start" : "__fini_array_start",
ArrayType::get(PtrTy, 0), [&]() {
return new GlobalVariable(
M, ArrayType::get(PtrTy, 0),
/*isConstant=*/true, GlobalValue::ExternalLinkage,
/*Initializer=*/nullptr,
IsCtor ? "__init_array_start" : "__fini_array_start",
/*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
/*AddressSpace=*/1);
});
auto *End = M.getOrInsertGlobal(
IsCtor ? "__init_array_end" : "__fini_array_end",
ArrayType::get(PtrTy, 0), [&]() {
return new GlobalVariable(
M, ArrayType::get(PtrTy, 0),
/*isConstant=*/true, GlobalValue::ExternalLinkage,
/*Initializer=*/nullptr,
IsCtor ? "__init_array_end" : "__fini_array_end",
/*InsertBefore=*/nullptr, GlobalVariable::NotThreadLocal,
/*AddressSpace=*/1);
});
// The constructor type is suppoed to allow using the argument vectors, but
// for now we just call them with no arguments.
auto *CallBackTy = FunctionType::get(IRB.getVoidTy(), {});
Value *Start = Begin;
Value *Stop = End;
// The destructor array must be called in reverse order. Get a constant
// expression to the end of the array and iterate backwards instead.
if (!IsCtor) {
Type *Int64Ty = IntegerType::getInt64Ty(C);
auto *EndPtr = IRB.CreatePtrToInt(End, Int64Ty);
auto *BeginPtr = IRB.CreatePtrToInt(Begin, Int64Ty);
auto *ByteSize = IRB.CreateSub(EndPtr, BeginPtr);
auto *Size = IRB.CreateAShr(ByteSize, ConstantInt::get(Int64Ty, 3));
auto *Offset = IRB.CreateSub(Size, ConstantInt::get(Int64Ty, 1));
Start = IRB.CreateInBoundsGEP(
ArrayType::get(IRB.getPtrTy(), 0), Begin,
ArrayRef<Value *>({ConstantInt::get(Int64Ty, 0), Offset}));
Stop = Begin;
}
IRB.CreateCondBr(
IRB.CreateCmp(IsCtor ? ICmpInst::ICMP_NE : ICmpInst::ICMP_UGE, Start,
Stop),
LoopBB, ExitBB);
IRB.SetInsertPoint(LoopBB);
auto *CallBackPHI = IRB.CreatePHI(PtrTy, 2, "ptr");
auto *CallBack = IRB.CreateLoad(IRB.getPtrTy(F.getAddressSpace()),
CallBackPHI, "callback");
IRB.CreateCall(CallBackTy, CallBack);
auto *NewCallBack =
IRB.CreateConstGEP1_64(PtrTy, CallBackPHI, IsCtor ? 1 : -1, "next");
auto *EndCmp = IRB.CreateCmp(IsCtor ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_ULT,
NewCallBack, Stop, "end");
CallBackPHI->addIncoming(Start, &F.getEntryBlock());
CallBackPHI->addIncoming(NewCallBack, LoopBB);
IRB.CreateCondBr(EndCmp, ExitBB, LoopBB);
IRB.SetInsertPoint(ExitBB);
IRB.CreateRetVoid();
}
static bool createInitOrFiniKernel(Module &M, StringRef GlobalName,
bool IsCtor) {
GlobalVariable *GV = M.getGlobalVariable(GlobalName);
if (!GV || !GV->hasInitializer())
return false;
ConstantArray *GA = dyn_cast<ConstantArray>(GV->getInitializer());
if (!GA || GA->getNumOperands() == 0)
return false;
Function *InitOrFiniKernel = createInitOrFiniKernelFunction(M, IsCtor);
if (!InitOrFiniKernel)
return false;
createInitOrFiniCalls(*InitOrFiniKernel, IsCtor);
appendToUsed(M, {InitOrFiniKernel});
return true;
}
static bool lowerCtorsAndDtors(Module &M) {
bool Modified = false;
Modified |= createInitOrFiniKernel(M, "llvm.global_ctors", /*IsCtor =*/true);
Modified |= createInitOrFiniKernel(M, "llvm.global_dtors", /*IsCtor =*/false);
return Modified;
}
class AMDGPUCtorDtorLoweringLegacy final : public ModulePass {
public:
static char ID;
AMDGPUCtorDtorLoweringLegacy() : ModulePass(ID) {}
bool runOnModule(Module &M) override { return lowerCtorsAndDtors(M); }
};
} // End anonymous namespace
PreservedAnalyses AMDGPUCtorDtorLoweringPass::run(Module &M,
ModuleAnalysisManager &AM) {
return lowerCtorsAndDtors(M) ? PreservedAnalyses::none()
: PreservedAnalyses::all();
}
char AMDGPUCtorDtorLoweringLegacy::ID = 0;
char &llvm::AMDGPUCtorDtorLoweringLegacyPassID =
AMDGPUCtorDtorLoweringLegacy::ID;
INITIALIZE_PASS(AMDGPUCtorDtorLoweringLegacy, DEBUG_TYPE,
"Lower ctors and dtors for AMDGPU", false, false)
ModulePass *llvm::createAMDGPUCtorDtorLoweringLegacyPass() {
return new AMDGPUCtorDtorLoweringLegacy();
}
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