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llvm-project/clang/lib/CodeGen/CGOpenMPRuntimeNVPTX.cpp

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//===---- CGOpenMPRuntimeNVPTX.cpp - Interface to OpenMP NVPTX Runtimes ---===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This provides a class for OpenMP runtime code generation specialized to NVPTX
// targets.
//
//===----------------------------------------------------------------------===//
#include "CGOpenMPRuntimeNVPTX.h"
#include "clang/AST/DeclOpenMP.h"
#include "CodeGenFunction.h"
#include "clang/AST/StmtOpenMP.h"
using namespace clang;
using namespace CodeGen;
namespace {
enum OpenMPRTLFunctionNVPTX {
/// \brief Call to void __kmpc_kernel_init(kmp_int32 thread_limit);
OMPRTL_NVPTX__kmpc_kernel_init,
/// \brief Call to void __kmpc_kernel_deinit();
OMPRTL_NVPTX__kmpc_kernel_deinit,
};
} // namespace
/// Get the GPU warp size.
static llvm::Value *getNVPTXWarpSize(CodeGenFunction &CGF) {
CGBuilderTy &Bld = CGF.Builder;
return Bld.CreateCall(
llvm::Intrinsic::getDeclaration(
&CGF.CGM.getModule(), llvm::Intrinsic::nvvm_read_ptx_sreg_warpsize),
llvm::None, "nvptx_warp_size");
}
/// Get the id of the current thread on the GPU.
static llvm::Value *getNVPTXThreadID(CodeGenFunction &CGF) {
CGBuilderTy &Bld = CGF.Builder;
return Bld.CreateCall(
llvm::Intrinsic::getDeclaration(
&CGF.CGM.getModule(), llvm::Intrinsic::nvvm_read_ptx_sreg_tid_x),
llvm::None, "nvptx_tid");
}
/// Get the maximum number of threads in a block of the GPU.
static llvm::Value *getNVPTXNumThreads(CodeGenFunction &CGF) {
CGBuilderTy &Bld = CGF.Builder;
return Bld.CreateCall(
llvm::Intrinsic::getDeclaration(
&CGF.CGM.getModule(), llvm::Intrinsic::nvvm_read_ptx_sreg_ntid_x),
llvm::None, "nvptx_num_threads");
}
/// Get barrier to synchronize all threads in a block.
static void getNVPTXCTABarrier(CodeGenFunction &CGF) {
CGBuilderTy &Bld = CGF.Builder;
Bld.CreateCall(llvm::Intrinsic::getDeclaration(
&CGF.CGM.getModule(), llvm::Intrinsic::nvvm_barrier0));
}
/// Synchronize all GPU threads in a block.
static void syncCTAThreads(CodeGenFunction &CGF) { getNVPTXCTABarrier(CGF); }
/// Get the value of the thread_limit clause in the teams directive.
/// The runtime encodes thread_limit in the launch parameter, always starting
/// thread_limit+warpSize threads per team.
static llvm::Value *getThreadLimit(CodeGenFunction &CGF) {
CGBuilderTy &Bld = CGF.Builder;
return Bld.CreateSub(getNVPTXNumThreads(CGF), getNVPTXWarpSize(CGF),
"thread_limit");
}
/// Get the thread id of the OMP master thread.
/// The master thread id is the first thread (lane) of the last warp in the
/// GPU block. Warp size is assumed to be some power of 2.
/// Thread id is 0 indexed.
/// E.g: If NumThreads is 33, master id is 32.
/// If NumThreads is 64, master id is 32.
/// If NumThreads is 1024, master id is 992.
static llvm::Value *getMasterThreadID(CodeGenFunction &CGF) {
CGBuilderTy &Bld = CGF.Builder;
llvm::Value *NumThreads = getNVPTXNumThreads(CGF);
// We assume that the warp size is a power of 2.
llvm::Value *Mask = Bld.CreateSub(getNVPTXWarpSize(CGF), Bld.getInt32(1));
return Bld.CreateAnd(Bld.CreateSub(NumThreads, Bld.getInt32(1)),
Bld.CreateNot(Mask), "master_tid");
}
CGOpenMPRuntimeNVPTX::WorkerFunctionState::WorkerFunctionState(
CodeGenModule &CGM)
: WorkerFn(nullptr), CGFI(nullptr) {
createWorkerFunction(CGM);
}
void CGOpenMPRuntimeNVPTX::WorkerFunctionState::createWorkerFunction(
CodeGenModule &CGM) {
// Create an worker function with no arguments.
CGFI = &CGM.getTypes().arrangeNullaryFunction();
WorkerFn = llvm::Function::Create(
CGM.getTypes().GetFunctionType(*CGFI), llvm::GlobalValue::InternalLinkage,
/* placeholder */ "_worker", &CGM.getModule());
CGM.SetInternalFunctionAttributes(/*D=*/nullptr, WorkerFn, *CGFI);
}
void CGOpenMPRuntimeNVPTX::emitGenericKernel(const OMPExecutableDirective &D,
StringRef ParentName,
llvm::Function *&OutlinedFn,
llvm::Constant *&OutlinedFnID,
bool IsOffloadEntry,
const RegionCodeGenTy &CodeGen) {
EntryFunctionState EST;
WorkerFunctionState WST(CGM);
// Emit target region as a standalone region.
class NVPTXPrePostActionTy : public PrePostActionTy {
CGOpenMPRuntimeNVPTX &RT;
CGOpenMPRuntimeNVPTX::EntryFunctionState &EST;
CGOpenMPRuntimeNVPTX::WorkerFunctionState &WST;
public:
NVPTXPrePostActionTy(CGOpenMPRuntimeNVPTX &RT,
CGOpenMPRuntimeNVPTX::EntryFunctionState &EST,
CGOpenMPRuntimeNVPTX::WorkerFunctionState &WST)
: RT(RT), EST(EST), WST(WST) {}
void Enter(CodeGenFunction &CGF) override {
RT.emitGenericEntryHeader(CGF, EST, WST);
}
void Exit(CodeGenFunction &CGF) override {
RT.emitGenericEntryFooter(CGF, EST);
}
} Action(*this, EST, WST);
CodeGen.setAction(Action);
emitTargetOutlinedFunctionHelper(D, ParentName, OutlinedFn, OutlinedFnID,
IsOffloadEntry, CodeGen);
// Create the worker function
emitWorkerFunction(WST);
// Now change the name of the worker function to correspond to this target
// region's entry function.
WST.WorkerFn->setName(OutlinedFn->getName() + "_worker");
}
// Setup NVPTX threads for master-worker OpenMP scheme.
void CGOpenMPRuntimeNVPTX::emitGenericEntryHeader(CodeGenFunction &CGF,
EntryFunctionState &EST,
WorkerFunctionState &WST) {
CGBuilderTy &Bld = CGF.Builder;
llvm::BasicBlock *WorkerBB = CGF.createBasicBlock(".worker");
llvm::BasicBlock *MasterCheckBB = CGF.createBasicBlock(".mastercheck");
llvm::BasicBlock *MasterBB = CGF.createBasicBlock(".master");
EST.ExitBB = CGF.createBasicBlock(".exit");
auto *IsWorker =
Bld.CreateICmpULT(getNVPTXThreadID(CGF), getThreadLimit(CGF));
Bld.CreateCondBr(IsWorker, WorkerBB, MasterCheckBB);
CGF.EmitBlock(WorkerBB);
CGF.EmitCallOrInvoke(WST.WorkerFn, llvm::None);
CGF.EmitBranch(EST.ExitBB);
CGF.EmitBlock(MasterCheckBB);
auto *IsMaster =
Bld.CreateICmpEQ(getNVPTXThreadID(CGF), getMasterThreadID(CGF));
Bld.CreateCondBr(IsMaster, MasterBB, EST.ExitBB);
CGF.EmitBlock(MasterBB);
// First action in sequential region:
// Initialize the state of the OpenMP runtime library on the GPU.
llvm::Value *Args[] = {getThreadLimit(CGF)};
CGF.EmitRuntimeCall(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_kernel_init), Args);
}
void CGOpenMPRuntimeNVPTX::emitGenericEntryFooter(CodeGenFunction &CGF,
EntryFunctionState &EST) {
if (!EST.ExitBB)
EST.ExitBB = CGF.createBasicBlock(".exit");
llvm::BasicBlock *TerminateBB = CGF.createBasicBlock(".termination.notifier");
CGF.EmitBranch(TerminateBB);
CGF.EmitBlock(TerminateBB);
// Signal termination condition.
CGF.EmitRuntimeCall(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_kernel_deinit), None);
// Barrier to terminate worker threads.
syncCTAThreads(CGF);
// Master thread jumps to exit point.
CGF.EmitBranch(EST.ExitBB);
CGF.EmitBlock(EST.ExitBB);
EST.ExitBB = nullptr;
}
void CGOpenMPRuntimeNVPTX::emitWorkerFunction(WorkerFunctionState &WST) {
auto &Ctx = CGM.getContext();
CodeGenFunction CGF(CGM, /*suppressNewContext=*/true);
CGF.disableDebugInfo();
CGF.StartFunction(GlobalDecl(), Ctx.VoidTy, WST.WorkerFn, *WST.CGFI, {});
emitWorkerLoop(CGF, WST);
CGF.FinishFunction();
}
void CGOpenMPRuntimeNVPTX::emitWorkerLoop(CodeGenFunction &CGF,
WorkerFunctionState &WST) {
//
// The workers enter this loop and wait for parallel work from the master.
// When the master encounters a parallel region it sets up the work + variable
// arguments, and wakes up the workers. The workers first check to see if
// they are required for the parallel region, i.e., within the # of requested
// parallel threads. The activated workers load the variable arguments and
// execute the parallel work.
//
CGBuilderTy &Bld = CGF.Builder;
llvm::BasicBlock *AwaitBB = CGF.createBasicBlock(".await.work");
llvm::BasicBlock *SelectWorkersBB = CGF.createBasicBlock(".select.workers");
llvm::BasicBlock *ExecuteBB = CGF.createBasicBlock(".execute.parallel");
llvm::BasicBlock *TerminateBB = CGF.createBasicBlock(".terminate.parallel");
llvm::BasicBlock *BarrierBB = CGF.createBasicBlock(".barrier.parallel");
llvm::BasicBlock *ExitBB = CGF.createBasicBlock(".exit");
CGF.EmitBranch(AwaitBB);
// Workers wait for work from master.
CGF.EmitBlock(AwaitBB);
// Wait for parallel work
syncCTAThreads(CGF);
Address WorkFn =
CGF.CreateDefaultAlignTempAlloca(CGF.Int8PtrTy, /*Name=*/"work_fn");
Address ExecStatus =
CGF.CreateDefaultAlignTempAlloca(CGF.Int8Ty, /*Name=*/"exec_status");
CGF.InitTempAlloca(ExecStatus, Bld.getInt8(/*C=*/0));
CGF.InitTempAlloca(WorkFn, llvm::Constant::getNullValue(CGF.Int8PtrTy));
// TODO: Call into runtime to get parallel work.
// On termination condition (workid == 0), exit loop.
llvm::Value *ShouldTerminate =
Bld.CreateIsNull(Bld.CreateLoad(WorkFn), "should_terminate");
Bld.CreateCondBr(ShouldTerminate, ExitBB, SelectWorkersBB);
// Activate requested workers.
CGF.EmitBlock(SelectWorkersBB);
llvm::Value *IsActive =
Bld.CreateIsNotNull(Bld.CreateLoad(ExecStatus), "is_active");
Bld.CreateCondBr(IsActive, ExecuteBB, BarrierBB);
// Signal start of parallel region.
CGF.EmitBlock(ExecuteBB);
// TODO: Add parallel work.
// Signal end of parallel region.
CGF.EmitBlock(TerminateBB);
CGF.EmitBranch(BarrierBB);
// All active and inactive workers wait at a barrier after parallel region.
CGF.EmitBlock(BarrierBB);
// Barrier after parallel region.
syncCTAThreads(CGF);
CGF.EmitBranch(AwaitBB);
// Exit target region.
CGF.EmitBlock(ExitBB);
}
/// \brief Returns specified OpenMP runtime function for the current OpenMP
/// implementation. Specialized for the NVPTX device.
/// \param Function OpenMP runtime function.
/// \return Specified function.
llvm::Constant *
CGOpenMPRuntimeNVPTX::createNVPTXRuntimeFunction(unsigned Function) {
llvm::Constant *RTLFn = nullptr;
switch (static_cast<OpenMPRTLFunctionNVPTX>(Function)) {
case OMPRTL_NVPTX__kmpc_kernel_init: {
// Build void __kmpc_kernel_init(kmp_int32 thread_limit);
llvm::Type *TypeParams[] = {CGM.Int32Ty};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.VoidTy, TypeParams, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_kernel_init");
break;
}
case OMPRTL_NVPTX__kmpc_kernel_deinit: {
// Build void __kmpc_kernel_deinit();
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.VoidTy, {}, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_kernel_deinit");
break;
}
}
return RTLFn;
}
void CGOpenMPRuntimeNVPTX::createOffloadEntry(llvm::Constant *ID,
llvm::Constant *Addr,
uint64_t Size, int32_t) {
auto *F = dyn_cast<llvm::Function>(Addr);
// TODO: Add support for global variables on the device after declare target
// support.
if (!F)
return;
llvm::Module *M = F->getParent();
llvm::LLVMContext &Ctx = M->getContext();
// Get "nvvm.annotations" metadata node
llvm::NamedMDNode *MD = M->getOrInsertNamedMetadata("nvvm.annotations");
llvm::Metadata *MDVals[] = {
llvm::ConstantAsMetadata::get(F), llvm::MDString::get(Ctx, "kernel"),
llvm::ConstantAsMetadata::get(
llvm::ConstantInt::get(llvm::Type::getInt32Ty(Ctx), 1))};
// Append metadata to nvvm.annotations
MD->addOperand(llvm::MDNode::get(Ctx, MDVals));
}
void CGOpenMPRuntimeNVPTX::emitTargetOutlinedFunction(
const OMPExecutableDirective &D, StringRef ParentName,
llvm::Function *&OutlinedFn, llvm::Constant *&OutlinedFnID,
bool IsOffloadEntry, const RegionCodeGenTy &CodeGen) {
if (!IsOffloadEntry) // Nothing to do.
return;
assert(!ParentName.empty() && "Invalid target region parent name!");
emitGenericKernel(D, ParentName, OutlinedFn, OutlinedFnID, IsOffloadEntry,
CodeGen);
}
CGOpenMPRuntimeNVPTX::CGOpenMPRuntimeNVPTX(CodeGenModule &CGM)
: CGOpenMPRuntime(CGM) {
if (!CGM.getLangOpts().OpenMPIsDevice)
llvm_unreachable("OpenMP NVPTX can only handle device code.");
}
void CGOpenMPRuntimeNVPTX::emitNumTeamsClause(CodeGenFunction &CGF,
const Expr *NumTeams,
const Expr *ThreadLimit,
SourceLocation Loc) {}
llvm::Value *CGOpenMPRuntimeNVPTX::emitParallelOrTeamsOutlinedFunction(
const OMPExecutableDirective &D, const VarDecl *ThreadIDVar,
OpenMPDirectiveKind InnermostKind, const RegionCodeGenTy &CodeGen) {
llvm::Function *OutlinedFun = nullptr;
if (isa<OMPTeamsDirective>(D)) {
llvm::Value *OutlinedFunVal =
CGOpenMPRuntime::emitParallelOrTeamsOutlinedFunction(
D, ThreadIDVar, InnermostKind, CodeGen);
OutlinedFun = cast<llvm::Function>(OutlinedFunVal);
OutlinedFun->removeFnAttr(llvm::Attribute::NoInline);
OutlinedFun->addFnAttr(llvm::Attribute::AlwaysInline);
} else
llvm_unreachable("parallel directive is not yet supported for nvptx "
"backend.");
return OutlinedFun;
}
void CGOpenMPRuntimeNVPTX::emitTeamsCall(CodeGenFunction &CGF,
const OMPExecutableDirective &D,
SourceLocation Loc,
llvm::Value *OutlinedFn,
ArrayRef<llvm::Value *> CapturedVars) {
if (!CGF.HaveInsertPoint())
return;
Address ZeroAddr =
CGF.CreateTempAlloca(CGF.Int32Ty, CharUnits::fromQuantity(4),
/*Name*/ ".zero.addr");
CGF.InitTempAlloca(ZeroAddr, CGF.Builder.getInt32(/*C*/ 0));
llvm::SmallVector<llvm::Value *, 16> OutlinedFnArgs;
OutlinedFnArgs.push_back(ZeroAddr.getPointer());
OutlinedFnArgs.push_back(ZeroAddr.getPointer());
OutlinedFnArgs.append(CapturedVars.begin(), CapturedVars.end());
CGF.EmitCallOrInvoke(OutlinedFn, OutlinedFnArgs);
}
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