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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,
/// \brief Call to void __kmpc_spmd_kernel_init(kmp_int32 thread_limit,
/// short RequiresOMPRuntime, short RequiresDataSharing);
OMPRTL_NVPTX__kmpc_spmd_kernel_init,
/// \brief Call to void __kmpc_spmd_kernel_deinit();
OMPRTL_NVPTX__kmpc_spmd_kernel_deinit,
/// \brief Call to void __kmpc_kernel_prepare_parallel(void
/// *outlined_function);
OMPRTL_NVPTX__kmpc_kernel_prepare_parallel,
/// \brief Call to bool __kmpc_kernel_parallel(void **outlined_function);
OMPRTL_NVPTX__kmpc_kernel_parallel,
/// \brief Call to void __kmpc_kernel_end_parallel();
OMPRTL_NVPTX__kmpc_kernel_end_parallel,
/// Call to void __kmpc_serialized_parallel(ident_t *loc, kmp_int32
/// global_tid);
OMPRTL_NVPTX__kmpc_serialized_parallel,
/// Call to void __kmpc_end_serialized_parallel(ident_t *loc, kmp_int32
/// global_tid);
OMPRTL_NVPTX__kmpc_end_serialized_parallel,
/// \brief Call to int32_t __kmpc_shuffle_int32(int32_t element,
/// int16_t lane_offset, int16_t warp_size);
OMPRTL_NVPTX__kmpc_shuffle_int32,
/// \brief Call to int64_t __kmpc_shuffle_int64(int64_t element,
/// int16_t lane_offset, int16_t warp_size);
OMPRTL_NVPTX__kmpc_shuffle_int64,
/// \brief Call to __kmpc_nvptx_parallel_reduce_nowait(kmp_int32
/// global_tid, kmp_int32 num_vars, size_t reduce_size, void* reduce_data,
/// void (*kmp_ShuffleReductFctPtr)(void *rhsData, int16_t lane_id, int16_t
/// lane_offset, int16_t shortCircuit),
/// void (*kmp_InterWarpCopyFctPtr)(void* src, int32_t warp_num));
OMPRTL_NVPTX__kmpc_parallel_reduce_nowait,
/// \brief Call to __kmpc_nvptx_teams_reduce_nowait(int32_t global_tid,
/// int32_t num_vars, size_t reduce_size, void *reduce_data,
/// void (*kmp_ShuffleReductFctPtr)(void *rhs, int16_t lane_id, int16_t
/// lane_offset, int16_t shortCircuit),
/// void (*kmp_InterWarpCopyFctPtr)(void* src, int32_t warp_num),
/// void (*kmp_CopyToScratchpadFctPtr)(void *reduce_data, void * scratchpad,
/// int32_t index, int32_t width),
/// void (*kmp_LoadReduceFctPtr)(void *reduce_data, void * scratchpad, int32_t
/// index, int32_t width, int32_t reduce))
OMPRTL_NVPTX__kmpc_teams_reduce_nowait,
/// \brief Call to __kmpc_nvptx_end_reduce_nowait(int32_t global_tid);
OMPRTL_NVPTX__kmpc_end_reduce_nowait
};
/// Pre(post)-action for different OpenMP constructs specialized for NVPTX.
class NVPTXActionTy final : public PrePostActionTy {
llvm::Value *EnterCallee;
ArrayRef<llvm::Value *> EnterArgs;
llvm::Value *ExitCallee;
ArrayRef<llvm::Value *> ExitArgs;
bool Conditional;
llvm::BasicBlock *ContBlock = nullptr;
public:
NVPTXActionTy(llvm::Value *EnterCallee, ArrayRef<llvm::Value *> EnterArgs,
llvm::Value *ExitCallee, ArrayRef<llvm::Value *> ExitArgs,
bool Conditional = false)
: EnterCallee(EnterCallee), EnterArgs(EnterArgs), ExitCallee(ExitCallee),
ExitArgs(ExitArgs), Conditional(Conditional) {}
void Enter(CodeGenFunction &CGF) override {
llvm::Value *EnterRes = CGF.EmitRuntimeCall(EnterCallee, EnterArgs);
if (Conditional) {
llvm::Value *CallBool = CGF.Builder.CreateIsNotNull(EnterRes);
auto *ThenBlock = CGF.createBasicBlock("omp_if.then");
ContBlock = CGF.createBasicBlock("omp_if.end");
// Generate the branch (If-stmt)
CGF.Builder.CreateCondBr(CallBool, ThenBlock, ContBlock);
CGF.EmitBlock(ThenBlock);
}
}
void Done(CodeGenFunction &CGF) {
// Emit the rest of blocks/branches
CGF.EmitBranch(ContBlock);
CGF.EmitBlock(ContBlock, true);
}
void Exit(CodeGenFunction &CGF) override {
CGF.EmitRuntimeCall(ExitCallee, ExitArgs);
}
};
// A class to track the execution mode when codegening directives within
// a target region. The appropriate mode (generic/spmd) is set on entry
// to the target region and used by containing directives such as 'parallel'
// to emit optimized code.
class ExecutionModeRAII {
private:
CGOpenMPRuntimeNVPTX::ExecutionMode SavedMode;
CGOpenMPRuntimeNVPTX::ExecutionMode &Mode;
public:
ExecutionModeRAII(CGOpenMPRuntimeNVPTX::ExecutionMode &Mode,
CGOpenMPRuntimeNVPTX::ExecutionMode NewMode)
: Mode(Mode) {
SavedMode = Mode;
Mode = NewMode;
}
~ExecutionModeRAII() { Mode = SavedMode; }
};
/// GPU Configuration: This information can be derived from cuda registers,
/// however, providing compile time constants helps generate more efficient
/// code. For all practical purposes this is fine because the configuration
/// is the same for all known NVPTX architectures.
enum MachineConfiguration : unsigned {
WarpSize = 32,
/// Number of bits required to represent a lane identifier, which is
/// computed as log_2(WarpSize).
LaneIDBits = 5,
LaneIDMask = WarpSize - 1,
/// Global memory alignment for performance.
GlobalMemoryAlignment = 256,
};
enum NamedBarrier : unsigned {
/// Synchronize on this barrier #ID using a named barrier primitive.
/// Only the subset of active threads in a parallel region arrive at the
/// barrier.
NB_Parallel = 1,
};
} // anonymous 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 id of the warp in the block.
/// We assume that the warp size is 32, which is always the case
/// on the NVPTX device, to generate more efficient code.
static llvm::Value *getNVPTXWarpID(CodeGenFunction &CGF) {
CGBuilderTy &Bld = CGF.Builder;
return Bld.CreateAShr(getNVPTXThreadID(CGF), LaneIDBits, "nvptx_warp_id");
}
/// Get the id of the current lane in the Warp.
/// We assume that the warp size is 32, which is always the case
/// on the NVPTX device, to generate more efficient code.
static llvm::Value *getNVPTXLaneID(CodeGenFunction &CGF) {
CGBuilderTy &Bld = CGF.Builder;
return Bld.CreateAnd(getNVPTXThreadID(CGF), Bld.getInt32(LaneIDMask),
"nvptx_lane_id");
}
/// 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));
}
/// Get barrier #ID to synchronize selected (multiple of warp size) threads in
/// a CTA.
static void getNVPTXBarrier(CodeGenFunction &CGF, int ID,
llvm::Value *NumThreads) {
CGBuilderTy &Bld = CGF.Builder;
llvm::Value *Args[] = {Bld.getInt32(ID), NumThreads};
Bld.CreateCall(llvm::Intrinsic::getDeclaration(&CGF.CGM.getModule(),
llvm::Intrinsic::nvvm_barrier),
Args);
}
/// Synchronize all GPU threads in a block.
static void syncCTAThreads(CodeGenFunction &CGF) { getNVPTXCTABarrier(CGF); }
/// Synchronize worker threads in a parallel region.
static void syncParallelThreads(CodeGenFunction &CGF, llvm::Value *NumThreads) {
return getNVPTXBarrier(CGF, NB_Parallel, NumThreads);
}
/// Get the value of the thread_limit clause in the teams directive.
/// For the 'generic' execution mode, the runtime encodes thread_limit in
/// the launch parameters, always starting thread_limit+warpSize threads per
/// CTA. The threads in the last warp are reserved for master execution.
/// For the 'spmd' execution mode, all threads in a CTA are part of the team.
static llvm::Value *getThreadLimit(CodeGenFunction &CGF,
bool IsInSpmdExecutionMode = false) {
CGBuilderTy &Bld = CGF.Builder;
return IsInSpmdExecutionMode
? getNVPTXNumThreads(CGF)
: 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);
}
bool CGOpenMPRuntimeNVPTX::isInSpmdExecutionMode() const {
return CurrentExecutionMode == CGOpenMPRuntimeNVPTX::ExecutionMode::Spmd;
}
static CGOpenMPRuntimeNVPTX::ExecutionMode
getExecutionModeForDirective(CodeGenModule &CGM,
const OMPExecutableDirective &D) {
OpenMPDirectiveKind DirectiveKind = D.getDirectiveKind();
switch (DirectiveKind) {
case OMPD_target:
case OMPD_target_teams:
return CGOpenMPRuntimeNVPTX::ExecutionMode::Generic;
case OMPD_target_parallel:
return CGOpenMPRuntimeNVPTX::ExecutionMode::Spmd;
default:
llvm_unreachable("Unsupported directive on NVPTX device.");
}
llvm_unreachable("Unsupported directive on NVPTX device.");
}
void CGOpenMPRuntimeNVPTX::emitGenericKernel(const OMPExecutableDirective &D,
StringRef ParentName,
llvm::Function *&OutlinedFn,
llvm::Constant *&OutlinedFnID,
bool IsOffloadEntry,
const RegionCodeGenTy &CodeGen) {
ExecutionModeRAII ModeRAII(CurrentExecutionMode,
CGOpenMPRuntimeNVPTX::ExecutionMode::Generic);
EntryFunctionState EST;
WorkerFunctionState WST(CGM);
Work.clear();
// 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::emitSpmdKernel(const OMPExecutableDirective &D,
StringRef ParentName,
llvm::Function *&OutlinedFn,
llvm::Constant *&OutlinedFnID,
bool IsOffloadEntry,
const RegionCodeGenTy &CodeGen) {
ExecutionModeRAII ModeRAII(CurrentExecutionMode,
CGOpenMPRuntimeNVPTX::ExecutionMode::Spmd);
EntryFunctionState EST;
// Emit target region as a standalone region.
class NVPTXPrePostActionTy : public PrePostActionTy {
CGOpenMPRuntimeNVPTX &RT;
CGOpenMPRuntimeNVPTX::EntryFunctionState &EST;
const OMPExecutableDirective &D;
public:
NVPTXPrePostActionTy(CGOpenMPRuntimeNVPTX &RT,
CGOpenMPRuntimeNVPTX::EntryFunctionState &EST,
const OMPExecutableDirective &D)
: RT(RT), EST(EST), D(D) {}
void Enter(CodeGenFunction &CGF) override {
RT.emitSpmdEntryHeader(CGF, EST, D);
}
void Exit(CodeGenFunction &CGF) override {
RT.emitSpmdEntryFooter(CGF, EST);
}
} Action(*this, EST, D);
CodeGen.setAction(Action);
emitTargetOutlinedFunctionHelper(D, ParentName, OutlinedFn, OutlinedFnID,
IsOffloadEntry, CodeGen);
return;
}
void CGOpenMPRuntimeNVPTX::emitSpmdEntryHeader(
CodeGenFunction &CGF, EntryFunctionState &EST,
const OMPExecutableDirective &D) {
auto &Bld = CGF.Builder;
// Setup BBs in entry function.
llvm::BasicBlock *ExecuteBB = CGF.createBasicBlock(".execute");
EST.ExitBB = CGF.createBasicBlock(".exit");
// Initialize the OMP state in the runtime; called by all active threads.
// TODO: Set RequiresOMPRuntime and RequiresDataSharing parameters
// based on code analysis of the target region.
llvm::Value *Args[] = {getThreadLimit(CGF, /*IsInSpmdExecutionMode=*/true),
/*RequiresOMPRuntime=*/Bld.getInt16(1),
/*RequiresDataSharing=*/Bld.getInt16(1)};
CGF.EmitRuntimeCall(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_spmd_kernel_init), Args);
CGF.EmitBranch(ExecuteBB);
CGF.EmitBlock(ExecuteBB);
}
void CGOpenMPRuntimeNVPTX::emitSpmdEntryFooter(CodeGenFunction &CGF,
EntryFunctionState &EST) {
if (!EST.ExitBB)
EST.ExitBB = CGF.createBasicBlock(".exit");
llvm::BasicBlock *OMPDeInitBB = CGF.createBasicBlock(".omp.deinit");
CGF.EmitBranch(OMPDeInitBB);
CGF.EmitBlock(OMPDeInitBB);
// DeInitialize the OMP state in the runtime; called by all active threads.
CGF.EmitRuntimeCall(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_spmd_kernel_deinit), None);
CGF.EmitBranch(EST.ExitBB);
CGF.EmitBlock(EST.ExitBB);
EST.ExitBB = nullptr;
}
// Create a unique global variable to indicate the execution mode of this target
// region. The execution mode is either 'generic', or 'spmd' depending on the
// target directive. This variable is picked up by the offload library to setup
// the device appropriately before kernel launch. If the execution mode is
// 'generic', the runtime reserves one warp for the master, otherwise, all
// warps participate in parallel work.
static void setPropertyExecutionMode(CodeGenModule &CGM, StringRef Name,
CGOpenMPRuntimeNVPTX::ExecutionMode Mode) {
(void)new llvm::GlobalVariable(
CGM.getModule(), CGM.Int8Ty, /*isConstant=*/true,
llvm::GlobalValue::WeakAnyLinkage,
llvm::ConstantInt::get(CGM.Int8Ty, Mode), Name + Twine("_exec_mode"));
}
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));
llvm::Value *Args[] = {WorkFn.getPointer()};
llvm::Value *Ret = CGF.EmitRuntimeCall(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_kernel_parallel), Args);
Bld.CreateStore(Bld.CreateZExt(Ret, CGF.Int8Ty), ExecStatus);
// 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);
// Process work items: outlined parallel functions.
for (auto *W : Work) {
// Try to match this outlined function.
auto *ID = Bld.CreatePointerBitCastOrAddrSpaceCast(W, CGM.Int8PtrTy);
llvm::Value *WorkFnMatch =
Bld.CreateICmpEQ(Bld.CreateLoad(WorkFn), ID, "work_match");
llvm::BasicBlock *ExecuteFNBB = CGF.createBasicBlock(".execute.fn");
llvm::BasicBlock *CheckNextBB = CGF.createBasicBlock(".check.next");
Bld.CreateCondBr(WorkFnMatch, ExecuteFNBB, CheckNextBB);
// Execute this outlined function.
CGF.EmitBlock(ExecuteFNBB);
// Insert call to work function.
// FIXME: Pass arguments to outlined function from master thread.
auto *Fn = cast<llvm::Function>(W);
Address ZeroAddr =
CGF.CreateDefaultAlignTempAlloca(CGF.Int32Ty, /*Name=*/".zero.addr");
CGF.InitTempAlloca(ZeroAddr, CGF.Builder.getInt32(/*C=*/0));
llvm::Value *FnArgs[] = {ZeroAddr.getPointer(), ZeroAddr.getPointer()};
CGF.EmitCallOrInvoke(Fn, FnArgs);
// Go to end of parallel region.
CGF.EmitBranch(TerminateBB);
CGF.EmitBlock(CheckNextBB);
}
// Signal end of parallel region.
CGF.EmitBlock(TerminateBB);
CGF.EmitRuntimeCall(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_kernel_end_parallel),
llvm::None);
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, llvm::None, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_kernel_deinit");
break;
}
case OMPRTL_NVPTX__kmpc_spmd_kernel_init: {
// Build void __kmpc_spmd_kernel_init(kmp_int32 thread_limit,
// short RequiresOMPRuntime, short RequiresDataSharing);
llvm::Type *TypeParams[] = {CGM.Int32Ty, CGM.Int16Ty, CGM.Int16Ty};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.VoidTy, TypeParams, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_spmd_kernel_init");
break;
}
case OMPRTL_NVPTX__kmpc_spmd_kernel_deinit: {
// Build void __kmpc_spmd_kernel_deinit();
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.VoidTy, llvm::None, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_spmd_kernel_deinit");
break;
}
case OMPRTL_NVPTX__kmpc_kernel_prepare_parallel: {
/// Build void __kmpc_kernel_prepare_parallel(
/// void *outlined_function);
llvm::Type *TypeParams[] = {CGM.Int8PtrTy};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.VoidTy, TypeParams, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_kernel_prepare_parallel");
break;
}
case OMPRTL_NVPTX__kmpc_kernel_parallel: {
/// Build bool __kmpc_kernel_parallel(void **outlined_function);
llvm::Type *TypeParams[] = {CGM.Int8PtrPtrTy};
llvm::Type *RetTy = CGM.getTypes().ConvertType(CGM.getContext().BoolTy);
llvm::FunctionType *FnTy =
llvm::FunctionType::get(RetTy, TypeParams, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_kernel_parallel");
break;
}
case OMPRTL_NVPTX__kmpc_kernel_end_parallel: {
/// Build void __kmpc_kernel_end_parallel();
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.VoidTy, llvm::None, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_kernel_end_parallel");
break;
}
case OMPRTL_NVPTX__kmpc_serialized_parallel: {
// Build void __kmpc_serialized_parallel(ident_t *loc, kmp_int32
// global_tid);
llvm::Type *TypeParams[] = {getIdentTyPointerTy(), CGM.Int32Ty};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.VoidTy, TypeParams, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_serialized_parallel");
break;
}
case OMPRTL_NVPTX__kmpc_end_serialized_parallel: {
// Build void __kmpc_end_serialized_parallel(ident_t *loc, kmp_int32
// global_tid);
llvm::Type *TypeParams[] = {getIdentTyPointerTy(), CGM.Int32Ty};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.VoidTy, TypeParams, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_end_serialized_parallel");
break;
}
case OMPRTL_NVPTX__kmpc_shuffle_int32: {
// Build int32_t __kmpc_shuffle_int32(int32_t element,
// int16_t lane_offset, int16_t warp_size);
llvm::Type *TypeParams[] = {CGM.Int32Ty, CGM.Int16Ty, CGM.Int16Ty};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.Int32Ty, TypeParams, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_shuffle_int32");
break;
}
case OMPRTL_NVPTX__kmpc_shuffle_int64: {
// Build int64_t __kmpc_shuffle_int64(int64_t element,
// int16_t lane_offset, int16_t warp_size);
llvm::Type *TypeParams[] = {CGM.Int64Ty, CGM.Int16Ty, CGM.Int16Ty};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.Int64Ty, TypeParams, /*isVarArg*/ false);
RTLFn = CGM.CreateRuntimeFunction(FnTy, "__kmpc_shuffle_int64");
break;
}
case OMPRTL_NVPTX__kmpc_parallel_reduce_nowait: {
// Build int32_t kmpc_nvptx_parallel_reduce_nowait(kmp_int32 global_tid,
// kmp_int32 num_vars, size_t reduce_size, void* reduce_data,
// void (*kmp_ShuffleReductFctPtr)(void *rhsData, int16_t lane_id, int16_t
// lane_offset, int16_t Algorithm Version),
// void (*kmp_InterWarpCopyFctPtr)(void* src, int warp_num));
llvm::Type *ShuffleReduceTypeParams[] = {CGM.VoidPtrTy, CGM.Int16Ty,
CGM.Int16Ty, CGM.Int16Ty};
auto *ShuffleReduceFnTy =
llvm::FunctionType::get(CGM.VoidTy, ShuffleReduceTypeParams,
/*isVarArg=*/false);
llvm::Type *InterWarpCopyTypeParams[] = {CGM.VoidPtrTy, CGM.Int32Ty};
auto *InterWarpCopyFnTy =
llvm::FunctionType::get(CGM.VoidTy, InterWarpCopyTypeParams,
/*isVarArg=*/false);
llvm::Type *TypeParams[] = {CGM.Int32Ty,
CGM.Int32Ty,
CGM.SizeTy,
CGM.VoidPtrTy,
ShuffleReduceFnTy->getPointerTo(),
InterWarpCopyFnTy->getPointerTo()};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.Int32Ty, TypeParams, /*isVarArg=*/false);
RTLFn = CGM.CreateRuntimeFunction(
FnTy, /*Name=*/"__kmpc_nvptx_parallel_reduce_nowait");
break;
}
case OMPRTL_NVPTX__kmpc_teams_reduce_nowait: {
// Build int32_t __kmpc_nvptx_teams_reduce_nowait(int32_t global_tid,
// int32_t num_vars, size_t reduce_size, void *reduce_data,
// void (*kmp_ShuffleReductFctPtr)(void *rhsData, int16_t lane_id, int16_t
// lane_offset, int16_t shortCircuit),
// void (*kmp_InterWarpCopyFctPtr)(void* src, int32_t warp_num),
// void (*kmp_CopyToScratchpadFctPtr)(void *reduce_data, void * scratchpad,
// int32_t index, int32_t width),
// void (*kmp_LoadReduceFctPtr)(void *reduce_data, void * scratchpad,
// int32_t index, int32_t width, int32_t reduce))
llvm::Type *ShuffleReduceTypeParams[] = {CGM.VoidPtrTy, CGM.Int16Ty,
CGM.Int16Ty, CGM.Int16Ty};
auto *ShuffleReduceFnTy =
llvm::FunctionType::get(CGM.VoidTy, ShuffleReduceTypeParams,
/*isVarArg=*/false);
llvm::Type *InterWarpCopyTypeParams[] = {CGM.VoidPtrTy, CGM.Int32Ty};
auto *InterWarpCopyFnTy =
llvm::FunctionType::get(CGM.VoidTy, InterWarpCopyTypeParams,
/*isVarArg=*/false);
llvm::Type *CopyToScratchpadTypeParams[] = {CGM.VoidPtrTy, CGM.VoidPtrTy,
CGM.Int32Ty, CGM.Int32Ty};
auto *CopyToScratchpadFnTy =
llvm::FunctionType::get(CGM.VoidTy, CopyToScratchpadTypeParams,
/*isVarArg=*/false);
llvm::Type *LoadReduceTypeParams[] = {
CGM.VoidPtrTy, CGM.VoidPtrTy, CGM.Int32Ty, CGM.Int32Ty, CGM.Int32Ty};
auto *LoadReduceFnTy =
llvm::FunctionType::get(CGM.VoidTy, LoadReduceTypeParams,
/*isVarArg=*/false);
llvm::Type *TypeParams[] = {CGM.Int32Ty,
CGM.Int32Ty,
CGM.SizeTy,
CGM.VoidPtrTy,
ShuffleReduceFnTy->getPointerTo(),
InterWarpCopyFnTy->getPointerTo(),
CopyToScratchpadFnTy->getPointerTo(),
LoadReduceFnTy->getPointerTo()};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.Int32Ty, TypeParams, /*isVarArg=*/false);
RTLFn = CGM.CreateRuntimeFunction(
FnTy, /*Name=*/"__kmpc_nvptx_teams_reduce_nowait");
break;
}
case OMPRTL_NVPTX__kmpc_end_reduce_nowait: {
// Build __kmpc_end_reduce_nowait(kmp_int32 global_tid);
llvm::Type *TypeParams[] = {CGM.Int32Ty};
llvm::FunctionType *FnTy =
llvm::FunctionType::get(CGM.VoidTy, TypeParams, /*isVarArg=*/false);
RTLFn = CGM.CreateRuntimeFunction(
FnTy, /*Name=*/"__kmpc_nvptx_end_reduce_nowait");
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!");
CGOpenMPRuntimeNVPTX::ExecutionMode Mode =
getExecutionModeForDirective(CGM, D);
switch (Mode) {
case CGOpenMPRuntimeNVPTX::ExecutionMode::Generic:
emitGenericKernel(D, ParentName, OutlinedFn, OutlinedFnID, IsOffloadEntry,
CodeGen);
break;
case CGOpenMPRuntimeNVPTX::ExecutionMode::Spmd:
emitSpmdKernel(D, ParentName, OutlinedFn, OutlinedFnID, IsOffloadEntry,
CodeGen);
break;
case CGOpenMPRuntimeNVPTX::ExecutionMode::Unknown:
llvm_unreachable(
"Unknown programming model for OpenMP directive on NVPTX target.");
}
setPropertyExecutionMode(CGM, OutlinedFn->getName(), Mode);
}
CGOpenMPRuntimeNVPTX::CGOpenMPRuntimeNVPTX(CodeGenModule &CGM)
: CGOpenMPRuntime(CGM), CurrentExecutionMode(ExecutionMode::Unknown) {
if (!CGM.getLangOpts().OpenMPIsDevice)
llvm_unreachable("OpenMP NVPTX can only handle device code.");
}
void CGOpenMPRuntimeNVPTX::emitProcBindClause(CodeGenFunction &CGF,
OpenMPProcBindClauseKind ProcBind,
SourceLocation Loc) {
// Do nothing in case of Spmd mode and L0 parallel.
// TODO: If in Spmd mode and L1 parallel emit the clause.
if (isInSpmdExecutionMode())
return;
CGOpenMPRuntime::emitProcBindClause(CGF, ProcBind, Loc);
}
void CGOpenMPRuntimeNVPTX::emitNumThreadsClause(CodeGenFunction &CGF,
llvm::Value *NumThreads,
SourceLocation Loc) {
// Do nothing in case of Spmd mode and L0 parallel.
// TODO: If in Spmd mode and L1 parallel emit the clause.
if (isInSpmdExecutionMode())
return;
CGOpenMPRuntime::emitNumThreadsClause(CGF, NumThreads, Loc);
}
void CGOpenMPRuntimeNVPTX::emitNumTeamsClause(CodeGenFunction &CGF,
const Expr *NumTeams,
const Expr *ThreadLimit,
SourceLocation Loc) {}
llvm::Value *CGOpenMPRuntimeNVPTX::emitParallelOutlinedFunction(
const OMPExecutableDirective &D, const VarDecl *ThreadIDVar,
OpenMPDirectiveKind InnermostKind, const RegionCodeGenTy &CodeGen) {
return CGOpenMPRuntime::emitParallelOutlinedFunction(D, ThreadIDVar,
InnermostKind, CodeGen);
}
llvm::Value *CGOpenMPRuntimeNVPTX::emitTeamsOutlinedFunction(
const OMPExecutableDirective &D, const VarDecl *ThreadIDVar,
OpenMPDirectiveKind InnermostKind, const RegionCodeGenTy &CodeGen) {
llvm::Value *OutlinedFunVal = CGOpenMPRuntime::emitTeamsOutlinedFunction(
D, ThreadIDVar, InnermostKind, CodeGen);
llvm::Function *OutlinedFun = cast<llvm::Function>(OutlinedFunVal);
OutlinedFun->removeFnAttr(llvm::Attribute::NoInline);
OutlinedFun->removeFnAttr(llvm::Attribute::OptimizeNone);
OutlinedFun->addFnAttr(llvm::Attribute::AlwaysInline);
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);
}
void CGOpenMPRuntimeNVPTX::emitParallelCall(
CodeGenFunction &CGF, SourceLocation Loc, llvm::Value *OutlinedFn,
ArrayRef<llvm::Value *> CapturedVars, const Expr *IfCond) {
if (!CGF.HaveInsertPoint())
return;
if (isInSpmdExecutionMode())
emitSpmdParallelCall(CGF, Loc, OutlinedFn, CapturedVars, IfCond);
else
emitGenericParallelCall(CGF, Loc, OutlinedFn, CapturedVars, IfCond);
}
void CGOpenMPRuntimeNVPTX::emitGenericParallelCall(
CodeGenFunction &CGF, SourceLocation Loc, llvm::Value *OutlinedFn,
ArrayRef<llvm::Value *> CapturedVars, const Expr *IfCond) {
llvm::Function *Fn = cast<llvm::Function>(OutlinedFn);
auto &&L0ParallelGen = [this, Fn](CodeGenFunction &CGF, PrePostActionTy &) {
CGBuilderTy &Bld = CGF.Builder;
// Prepare for parallel region. Indicate the outlined function.
llvm::Value *Args[] = {Bld.CreateBitOrPointerCast(Fn, CGM.Int8PtrTy)};
CGF.EmitRuntimeCall(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_kernel_prepare_parallel),
Args);
// Activate workers. This barrier is used by the master to signal
// work for the workers.
syncCTAThreads(CGF);
// OpenMP [2.5, Parallel Construct, p.49]
// There is an implied barrier at the end of a parallel region. After the
// end of a parallel region, only the master thread of the team resumes
// execution of the enclosing task region.
//
// The master waits at this barrier until all workers are done.
syncCTAThreads(CGF);
// Remember for post-processing in worker loop.
Work.push_back(Fn);
};
auto *RTLoc = emitUpdateLocation(CGF, Loc);
auto *ThreadID = getThreadID(CGF, Loc);
llvm::Value *Args[] = {RTLoc, ThreadID};
auto &&SeqGen = [this, Fn, &CapturedVars, &Args](CodeGenFunction &CGF,
PrePostActionTy &) {
auto &&CodeGen = [this, Fn, &CapturedVars](CodeGenFunction &CGF,
PrePostActionTy &Action) {
Action.Enter(CGF);
llvm::SmallVector<llvm::Value *, 16> OutlinedFnArgs;
OutlinedFnArgs.push_back(
llvm::ConstantPointerNull::get(CGM.Int32Ty->getPointerTo()));
OutlinedFnArgs.push_back(
llvm::ConstantPointerNull::get(CGM.Int32Ty->getPointerTo()));
OutlinedFnArgs.append(CapturedVars.begin(), CapturedVars.end());
CGF.EmitCallOrInvoke(Fn, OutlinedFnArgs);
};
RegionCodeGenTy RCG(CodeGen);
NVPTXActionTy Action(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_serialized_parallel),
Args,
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_end_serialized_parallel),
Args);
RCG.setAction(Action);
RCG(CGF);
};
if (IfCond)
emitOMPIfClause(CGF, IfCond, L0ParallelGen, SeqGen);
else {
CodeGenFunction::RunCleanupsScope Scope(CGF);
RegionCodeGenTy ThenRCG(L0ParallelGen);
ThenRCG(CGF);
}
}
void CGOpenMPRuntimeNVPTX::emitSpmdParallelCall(
CodeGenFunction &CGF, SourceLocation Loc, llvm::Value *OutlinedFn,
ArrayRef<llvm::Value *> CapturedVars, const Expr *IfCond) {
// Just call the outlined function to execute the parallel region.
// OutlinedFn(&GTid, &zero, CapturedStruct);
//
// TODO: Do something with IfCond when support for the 'if' clause
// is added on Spmd target directives.
llvm::SmallVector<llvm::Value *, 16> OutlinedFnArgs;
OutlinedFnArgs.push_back(
llvm::ConstantPointerNull::get(CGM.Int32Ty->getPointerTo()));
OutlinedFnArgs.push_back(
llvm::ConstantPointerNull::get(CGM.Int32Ty->getPointerTo()));
OutlinedFnArgs.append(CapturedVars.begin(), CapturedVars.end());
CGF.EmitCallOrInvoke(OutlinedFn, OutlinedFnArgs);
}
/// This function creates calls to one of two shuffle functions to copy
/// variables between lanes in a warp.
static llvm::Value *createRuntimeShuffleFunction(CodeGenFunction &CGF,
QualType ElemTy,
llvm::Value *Elem,
llvm::Value *Offset) {
auto &CGM = CGF.CGM;
auto &C = CGM.getContext();
auto &Bld = CGF.Builder;
CGOpenMPRuntimeNVPTX &RT =
*(static_cast<CGOpenMPRuntimeNVPTX *>(&CGM.getOpenMPRuntime()));
unsigned Size = CGM.getContext().getTypeSizeInChars(ElemTy).getQuantity();
assert(Size <= 8 && "Unsupported bitwidth in shuffle instruction.");
OpenMPRTLFunctionNVPTX ShuffleFn = Size <= 4
? OMPRTL_NVPTX__kmpc_shuffle_int32
: OMPRTL_NVPTX__kmpc_shuffle_int64;
// Cast all types to 32- or 64-bit values before calling shuffle routines.
auto CastTy = Size <= 4 ? CGM.Int32Ty : CGM.Int64Ty;
auto *ElemCast = Bld.CreateSExtOrBitCast(Elem, CastTy);
auto *WarpSize = CGF.EmitScalarConversion(
getNVPTXWarpSize(CGF), C.getIntTypeForBitwidth(32, /* Signed */ true),
C.getIntTypeForBitwidth(16, /* Signed */ true), SourceLocation());
auto *ShuffledVal =
CGF.EmitRuntimeCall(RT.createNVPTXRuntimeFunction(ShuffleFn),
{ElemCast, Offset, WarpSize});
return Bld.CreateTruncOrBitCast(ShuffledVal, CGF.ConvertTypeForMem(ElemTy));
}
namespace {
enum CopyAction : unsigned {
// RemoteLaneToThread: Copy over a Reduce list from a remote lane in
// the warp using shuffle instructions.
RemoteLaneToThread,
// ThreadCopy: Make a copy of a Reduce list on the thread's stack.
ThreadCopy,
// ThreadToScratchpad: Copy a team-reduced array to the scratchpad.
ThreadToScratchpad,
// ScratchpadToThread: Copy from a scratchpad array in global memory
// containing team-reduced data to a thread's stack.
ScratchpadToThread,
};
} // namespace
struct CopyOptionsTy {
llvm::Value *RemoteLaneOffset;
llvm::Value *ScratchpadIndex;
llvm::Value *ScratchpadWidth;
};
/// Emit instructions to copy a Reduce list, which contains partially
/// aggregated values, in the specified direction.
static void emitReductionListCopy(
CopyAction Action, CodeGenFunction &CGF, QualType ReductionArrayTy,
ArrayRef<const Expr *> Privates, Address SrcBase, Address DestBase,
CopyOptionsTy CopyOptions = {nullptr, nullptr, nullptr}) {
auto &CGM = CGF.CGM;
auto &C = CGM.getContext();
auto &Bld = CGF.Builder;
auto *RemoteLaneOffset = CopyOptions.RemoteLaneOffset;
auto *ScratchpadIndex = CopyOptions.ScratchpadIndex;
auto *ScratchpadWidth = CopyOptions.ScratchpadWidth;
// Iterates, element-by-element, through the source Reduce list and
// make a copy.
unsigned Idx = 0;
unsigned Size = Privates.size();
for (auto &Private : Privates) {
Address SrcElementAddr = Address::invalid();
Address DestElementAddr = Address::invalid();
Address DestElementPtrAddr = Address::invalid();
// Should we shuffle in an element from a remote lane?
bool ShuffleInElement = false;
// Set to true to update the pointer in the dest Reduce list to a
// newly created element.
bool UpdateDestListPtr = false;
// Increment the src or dest pointer to the scratchpad, for each
// new element.
bool IncrScratchpadSrc = false;
bool IncrScratchpadDest = false;
switch (Action) {
case RemoteLaneToThread: {
// Step 1.1: Get the address for the src element in the Reduce list.
Address SrcElementPtrAddr =
Bld.CreateConstArrayGEP(SrcBase, Idx, CGF.getPointerSize());
llvm::Value *SrcElementPtrPtr = CGF.EmitLoadOfScalar(
SrcElementPtrAddr, /*Volatile=*/false, C.VoidPtrTy, SourceLocation());
SrcElementAddr =
Address(SrcElementPtrPtr, C.getTypeAlignInChars(Private->getType()));
// Step 1.2: Create a temporary to store the element in the destination
// Reduce list.
DestElementPtrAddr =
Bld.CreateConstArrayGEP(DestBase, Idx, CGF.getPointerSize());
DestElementAddr =
CGF.CreateMemTemp(Private->getType(), ".omp.reduction.element");
ShuffleInElement = true;
UpdateDestListPtr = true;
break;
}
case ThreadCopy: {
// Step 1.1: Get the address for the src element in the Reduce list.
Address SrcElementPtrAddr =
Bld.CreateConstArrayGEP(SrcBase, Idx, CGF.getPointerSize());
llvm::Value *SrcElementPtrPtr = CGF.EmitLoadOfScalar(
SrcElementPtrAddr, /*Volatile=*/false, C.VoidPtrTy, SourceLocation());
SrcElementAddr =
Address(SrcElementPtrPtr, C.getTypeAlignInChars(Private->getType()));
// Step 1.2: Get the address for dest element. The destination
// element has already been created on the thread's stack.
DestElementPtrAddr =
Bld.CreateConstArrayGEP(DestBase, Idx, CGF.getPointerSize());
llvm::Value *DestElementPtr =
CGF.EmitLoadOfScalar(DestElementPtrAddr, /*Volatile=*/false,
C.VoidPtrTy, SourceLocation());
Address DestElemAddr =
Address(DestElementPtr, C.getTypeAlignInChars(Private->getType()));
DestElementAddr = Bld.CreateElementBitCast(
DestElemAddr, CGF.ConvertTypeForMem(Private->getType()));
break;
}
case ThreadToScratchpad: {
// Step 1.1: Get the address for the src element in the Reduce list.
Address SrcElementPtrAddr =
Bld.CreateConstArrayGEP(SrcBase, Idx, CGF.getPointerSize());
llvm::Value *SrcElementPtrPtr = CGF.EmitLoadOfScalar(
SrcElementPtrAddr, /*Volatile=*/false, C.VoidPtrTy, SourceLocation());
SrcElementAddr =
Address(SrcElementPtrPtr, C.getTypeAlignInChars(Private->getType()));
// Step 1.2: Get the address for dest element:
// address = base + index * ElementSizeInChars.
unsigned ElementSizeInChars =
C.getTypeSizeInChars(Private->getType()).getQuantity();
auto *CurrentOffset =
Bld.CreateMul(llvm::ConstantInt::get(CGM.SizeTy, ElementSizeInChars),
ScratchpadIndex);
auto *ScratchPadElemAbsolutePtrVal =
Bld.CreateAdd(DestBase.getPointer(), CurrentOffset);
ScratchPadElemAbsolutePtrVal =
Bld.CreateIntToPtr(ScratchPadElemAbsolutePtrVal, CGF.VoidPtrTy);
Address ScratchpadPtr =
Address(ScratchPadElemAbsolutePtrVal,
C.getTypeAlignInChars(Private->getType()));
DestElementAddr = Bld.CreateElementBitCast(
ScratchpadPtr, CGF.ConvertTypeForMem(Private->getType()));
IncrScratchpadDest = true;
break;
}
case ScratchpadToThread: {
// Step 1.1: Get the address for the src element in the scratchpad.
// address = base + index * ElementSizeInChars.
unsigned ElementSizeInChars =
C.getTypeSizeInChars(Private->getType()).getQuantity();
auto *CurrentOffset =
Bld.CreateMul(llvm::ConstantInt::get(CGM.SizeTy, ElementSizeInChars),
ScratchpadIndex);
auto *ScratchPadElemAbsolutePtrVal =
Bld.CreateAdd(SrcBase.getPointer(), CurrentOffset);
ScratchPadElemAbsolutePtrVal =
Bld.CreateIntToPtr(ScratchPadElemAbsolutePtrVal, CGF.VoidPtrTy);
SrcElementAddr = Address(ScratchPadElemAbsolutePtrVal,
C.getTypeAlignInChars(Private->getType()));
IncrScratchpadSrc = true;
// Step 1.2: Create a temporary to store the element in the destination
// Reduce list.
DestElementPtrAddr =
Bld.CreateConstArrayGEP(DestBase, Idx, CGF.getPointerSize());
DestElementAddr =
CGF.CreateMemTemp(Private->getType(), ".omp.reduction.element");
UpdateDestListPtr = true;
break;
}
}
// Regardless of src and dest of copy, we emit the load of src
// element as this is required in all directions
SrcElementAddr = Bld.CreateElementBitCast(
SrcElementAddr, CGF.ConvertTypeForMem(Private->getType()));
llvm::Value *Elem =
CGF.EmitLoadOfScalar(SrcElementAddr, /*Volatile=*/false,
Private->getType(), SourceLocation());
// Now that all active lanes have read the element in the
// Reduce list, shuffle over the value from the remote lane.
if (ShuffleInElement) {
Elem = createRuntimeShuffleFunction(CGF, Private->getType(), Elem,
RemoteLaneOffset);
}
// Store the source element value to the dest element address.
CGF.EmitStoreOfScalar(Elem, DestElementAddr, /*Volatile=*/false,
Private->getType());
// Step 3.1: Modify reference in dest Reduce list as needed.
// Modifying the reference in Reduce list to point to the newly
// created element. The element is live in the current function
// scope and that of functions it invokes (i.e., reduce_function).
// RemoteReduceData[i] = (void*)&RemoteElem
if (UpdateDestListPtr) {
CGF.EmitStoreOfScalar(Bld.CreatePointerBitCastOrAddrSpaceCast(
DestElementAddr.getPointer(), CGF.VoidPtrTy),
DestElementPtrAddr, /*Volatile=*/false,
C.VoidPtrTy);
}
// Step 4.1: Increment SrcBase/DestBase so that it points to the starting
// address of the next element in scratchpad memory, unless we're currently
// processing the last one. Memory alignment is also taken care of here.
if ((IncrScratchpadDest || IncrScratchpadSrc) && (Idx + 1 < Size)) {
llvm::Value *ScratchpadBasePtr =
IncrScratchpadDest ? DestBase.getPointer() : SrcBase.getPointer();
unsigned ElementSizeInChars =
C.getTypeSizeInChars(Private->getType()).getQuantity();
ScratchpadBasePtr = Bld.CreateAdd(
ScratchpadBasePtr,
Bld.CreateMul(ScratchpadWidth, llvm::ConstantInt::get(
CGM.SizeTy, ElementSizeInChars)));
// Take care of global memory alignment for performance
ScratchpadBasePtr = Bld.CreateSub(ScratchpadBasePtr,
llvm::ConstantInt::get(CGM.SizeTy, 1));
ScratchpadBasePtr = Bld.CreateSDiv(
ScratchpadBasePtr,
llvm::ConstantInt::get(CGM.SizeTy, GlobalMemoryAlignment));
ScratchpadBasePtr = Bld.CreateAdd(ScratchpadBasePtr,
llvm::ConstantInt::get(CGM.SizeTy, 1));
ScratchpadBasePtr = Bld.CreateMul(
ScratchpadBasePtr,
llvm::ConstantInt::get(CGM.SizeTy, GlobalMemoryAlignment));
if (IncrScratchpadDest)
DestBase = Address(ScratchpadBasePtr, CGF.getPointerAlign());
else /* IncrScratchpadSrc = true */
SrcBase = Address(ScratchpadBasePtr, CGF.getPointerAlign());
}
Idx++;
}
}
/// This function emits a helper that loads data from the scratchpad array
/// and (optionally) reduces it with the input operand.
///
/// load_and_reduce(local, scratchpad, index, width, should_reduce)
/// reduce_data remote;
/// for elem in remote:
/// remote.elem = Scratchpad[elem_id][index]
/// if (should_reduce)
/// local = local @ remote
/// else
/// local = remote
static llvm::Value *
emitReduceScratchpadFunction(CodeGenModule &CGM,
ArrayRef<const Expr *> Privates,
QualType ReductionArrayTy, llvm::Value *ReduceFn) {
auto &C = CGM.getContext();
auto Int32Ty = C.getIntTypeForBitwidth(32, /* Signed */ true);
// Destination of the copy.
ImplicitParamDecl ReduceListArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, C.VoidPtrTy);
// Base address of the scratchpad array, with each element storing a
// Reduce list per team.
ImplicitParamDecl ScratchPadArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, C.VoidPtrTy);
// A source index into the scratchpad array.
ImplicitParamDecl IndexArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, Int32Ty);
// Row width of an element in the scratchpad array, typically
// the number of teams.
ImplicitParamDecl WidthArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, Int32Ty);
// If should_reduce == 1, then it's load AND reduce,
// If should_reduce == 0 (or otherwise), then it only loads (+ copy).
// The latter case is used for initialization.
ImplicitParamDecl ShouldReduceArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, Int32Ty);
FunctionArgList Args;
Args.push_back(&ReduceListArg);
Args.push_back(&ScratchPadArg);
Args.push_back(&IndexArg);
Args.push_back(&WidthArg);
Args.push_back(&ShouldReduceArg);
auto &CGFI = CGM.getTypes().arrangeBuiltinFunctionDeclaration(C.VoidTy, Args);
auto *Fn = llvm::Function::Create(
CGM.getTypes().GetFunctionType(CGFI), llvm::GlobalValue::InternalLinkage,
"_omp_reduction_load_and_reduce", &CGM.getModule());
CGM.SetInternalFunctionAttributes(/*DC=*/nullptr, Fn, CGFI);
CodeGenFunction CGF(CGM);
// We don't need debug information in this function as nothing here refers to
// user code.
CGF.disableDebugInfo();
CGF.StartFunction(GlobalDecl(), C.VoidTy, Fn, CGFI, Args);
auto &Bld = CGF.Builder;
// Get local Reduce list pointer.
Address AddrReduceListArg = CGF.GetAddrOfLocalVar(&ReduceListArg);
Address ReduceListAddr(
Bld.CreatePointerBitCastOrAddrSpaceCast(
CGF.EmitLoadOfScalar(AddrReduceListArg, /*Volatile=*/false,
C.VoidPtrTy, SourceLocation()),
CGF.ConvertTypeForMem(ReductionArrayTy)->getPointerTo()),
CGF.getPointerAlign());
Address AddrScratchPadArg = CGF.GetAddrOfLocalVar(&ScratchPadArg);
llvm::Value *ScratchPadBase = CGF.EmitLoadOfScalar(
AddrScratchPadArg, /*Volatile=*/false, C.VoidPtrTy, SourceLocation());
Address AddrIndexArg = CGF.GetAddrOfLocalVar(&IndexArg);
llvm::Value *IndexVal =
Bld.CreateIntCast(CGF.EmitLoadOfScalar(AddrIndexArg, /*Volatile=*/false,
Int32Ty, SourceLocation()),
CGM.SizeTy, /*isSigned=*/true);
Address AddrWidthArg = CGF.GetAddrOfLocalVar(&WidthArg);
llvm::Value *WidthVal =
Bld.CreateIntCast(CGF.EmitLoadOfScalar(AddrWidthArg, /*Volatile=*/false,
Int32Ty, SourceLocation()),
CGM.SizeTy, /*isSigned=*/true);
Address AddrShouldReduceArg = CGF.GetAddrOfLocalVar(&ShouldReduceArg);
llvm::Value *ShouldReduceVal = CGF.EmitLoadOfScalar(
AddrShouldReduceArg, /*Volatile=*/false, Int32Ty, SourceLocation());
// The absolute ptr address to the base addr of the next element to copy.
llvm::Value *CumulativeElemBasePtr =
Bld.CreatePtrToInt(ScratchPadBase, CGM.SizeTy);
Address SrcDataAddr(CumulativeElemBasePtr, CGF.getPointerAlign());
// Create a Remote Reduce list to store the elements read from the
// scratchpad array.
Address RemoteReduceList =
CGF.CreateMemTemp(ReductionArrayTy, ".omp.reduction.remote_red_list");
// Assemble remote Reduce list from scratchpad array.
emitReductionListCopy(ScratchpadToThread, CGF, ReductionArrayTy, Privates,
SrcDataAddr, RemoteReduceList,
{/*RemoteLaneOffset=*/nullptr,
/*ScratchpadIndex=*/IndexVal,
/*ScratchpadWidth=*/WidthVal});
llvm::BasicBlock *ThenBB = CGF.createBasicBlock("then");
llvm::BasicBlock *ElseBB = CGF.createBasicBlock("else");
llvm::BasicBlock *MergeBB = CGF.createBasicBlock("ifcont");
auto CondReduce = Bld.CreateICmpEQ(ShouldReduceVal, Bld.getInt32(1));
Bld.CreateCondBr(CondReduce, ThenBB, ElseBB);
CGF.EmitBlock(ThenBB);
// We should reduce with the local Reduce list.
// reduce_function(LocalReduceList, RemoteReduceList)
llvm::Value *LocalDataPtr = Bld.CreatePointerBitCastOrAddrSpaceCast(
ReduceListAddr.getPointer(), CGF.VoidPtrTy);
llvm::Value *RemoteDataPtr = Bld.CreatePointerBitCastOrAddrSpaceCast(
RemoteReduceList.getPointer(), CGF.VoidPtrTy);
CGF.EmitCallOrInvoke(ReduceFn, {LocalDataPtr, RemoteDataPtr});
Bld.CreateBr(MergeBB);
CGF.EmitBlock(ElseBB);
// No reduction; just copy:
// Local Reduce list = Remote Reduce list.
emitReductionListCopy(ThreadCopy, CGF, ReductionArrayTy, Privates,
RemoteReduceList, ReduceListAddr);
Bld.CreateBr(MergeBB);
CGF.EmitBlock(MergeBB);
CGF.FinishFunction();
return Fn;
}
/// This function emits a helper that stores reduced data from the team
/// master to a scratchpad array in global memory.
///
/// for elem in Reduce List:
/// scratchpad[elem_id][index] = elem
///
static llvm::Value *emitCopyToScratchpad(CodeGenModule &CGM,
ArrayRef<const Expr *> Privates,
QualType ReductionArrayTy) {
auto &C = CGM.getContext();
auto Int32Ty = C.getIntTypeForBitwidth(32, /* Signed */ true);
// Source of the copy.
ImplicitParamDecl ReduceListArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, C.VoidPtrTy);
// Base address of the scratchpad array, with each element storing a
// Reduce list per team.
ImplicitParamDecl ScratchPadArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, C.VoidPtrTy);
// A destination index into the scratchpad array, typically the team
// identifier.
ImplicitParamDecl IndexArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, Int32Ty);
// Row width of an element in the scratchpad array, typically
// the number of teams.
ImplicitParamDecl WidthArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, Int32Ty);
FunctionArgList Args;
Args.push_back(&ReduceListArg);
Args.push_back(&ScratchPadArg);
Args.push_back(&IndexArg);
Args.push_back(&WidthArg);
auto &CGFI = CGM.getTypes().arrangeBuiltinFunctionDeclaration(C.VoidTy, Args);
auto *Fn = llvm::Function::Create(
CGM.getTypes().GetFunctionType(CGFI), llvm::GlobalValue::InternalLinkage,
"_omp_reduction_copy_to_scratchpad", &CGM.getModule());
CGM.SetInternalFunctionAttributes(/*DC=*/nullptr, Fn, CGFI);
CodeGenFunction CGF(CGM);
// We don't need debug information in this function as nothing here refers to
// user code.
CGF.disableDebugInfo();
CGF.StartFunction(GlobalDecl(), C.VoidTy, Fn, CGFI, Args);
auto &Bld = CGF.Builder;
Address AddrReduceListArg = CGF.GetAddrOfLocalVar(&ReduceListArg);
Address SrcDataAddr(
Bld.CreatePointerBitCastOrAddrSpaceCast(
CGF.EmitLoadOfScalar(AddrReduceListArg, /*Volatile=*/false,
C.VoidPtrTy, SourceLocation()),
CGF.ConvertTypeForMem(ReductionArrayTy)->getPointerTo()),
CGF.getPointerAlign());
Address AddrScratchPadArg = CGF.GetAddrOfLocalVar(&ScratchPadArg);
llvm::Value *ScratchPadBase = CGF.EmitLoadOfScalar(
AddrScratchPadArg, /*Volatile=*/false, C.VoidPtrTy, SourceLocation());
Address AddrIndexArg = CGF.GetAddrOfLocalVar(&IndexArg);
llvm::Value *IndexVal =
Bld.CreateIntCast(CGF.EmitLoadOfScalar(AddrIndexArg, /*Volatile=*/false,
Int32Ty, SourceLocation()),
CGF.SizeTy, /*isSigned=*/true);
Address AddrWidthArg = CGF.GetAddrOfLocalVar(&WidthArg);
llvm::Value *WidthVal =
Bld.CreateIntCast(CGF.EmitLoadOfScalar(AddrWidthArg, /*Volatile=*/false,
Int32Ty, SourceLocation()),
CGF.SizeTy, /*isSigned=*/true);
// The absolute ptr address to the base addr of the next element to copy.
llvm::Value *CumulativeElemBasePtr =
Bld.CreatePtrToInt(ScratchPadBase, CGM.SizeTy);
Address DestDataAddr(CumulativeElemBasePtr, CGF.getPointerAlign());
emitReductionListCopy(ThreadToScratchpad, CGF, ReductionArrayTy, Privates,
SrcDataAddr, DestDataAddr,
{/*RemoteLaneOffset=*/nullptr,
/*ScratchpadIndex=*/IndexVal,
/*ScratchpadWidth=*/WidthVal});
CGF.FinishFunction();
return Fn;
}
/// This function emits a helper that gathers Reduce lists from the first
/// lane of every active warp to lanes in the first warp.
///
/// void inter_warp_copy_func(void* reduce_data, num_warps)
/// shared smem[warp_size];
/// For all data entries D in reduce_data:
/// If (I am the first lane in each warp)
/// Copy my local D to smem[warp_id]
/// sync
/// if (I am the first warp)
/// Copy smem[thread_id] to my local D
/// sync
static llvm::Value *emitInterWarpCopyFunction(CodeGenModule &CGM,
ArrayRef<const Expr *> Privates,
QualType ReductionArrayTy) {
auto &C = CGM.getContext();
auto &M = CGM.getModule();
// ReduceList: thread local Reduce list.
// At the stage of the computation when this function is called, partially
// aggregated values reside in the first lane of every active warp.
ImplicitParamDecl ReduceListArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, C.VoidPtrTy);
// NumWarps: number of warps active in the parallel region. This could
// be smaller than 32 (max warps in a CTA) for partial block reduction.
ImplicitParamDecl NumWarpsArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr,
C.getIntTypeForBitwidth(32, /* Signed */ true));
FunctionArgList Args;
Args.push_back(&ReduceListArg);
Args.push_back(&NumWarpsArg);
auto &CGFI = CGM.getTypes().arrangeBuiltinFunctionDeclaration(C.VoidTy, Args);
auto *Fn = llvm::Function::Create(
CGM.getTypes().GetFunctionType(CGFI), llvm::GlobalValue::InternalLinkage,
"_omp_reduction_inter_warp_copy_func", &CGM.getModule());
CGM.SetInternalFunctionAttributes(/*DC=*/nullptr, Fn, CGFI);
CodeGenFunction CGF(CGM);
// We don't need debug information in this function as nothing here refers to
// user code.
CGF.disableDebugInfo();
CGF.StartFunction(GlobalDecl(), C.VoidTy, Fn, CGFI, Args);
auto &Bld = CGF.Builder;
// This array is used as a medium to transfer, one reduce element at a time,
// the data from the first lane of every warp to lanes in the first warp
// in order to perform the final step of a reduction in a parallel region
// (reduction across warps). The array is placed in NVPTX __shared__ memory
// for reduced latency, as well as to have a distinct copy for concurrently
// executing target regions. The array is declared with common linkage so
// as to be shared across compilation units.
const char *TransferMediumName =
"__openmp_nvptx_data_transfer_temporary_storage";
llvm::GlobalVariable *TransferMedium =
M.getGlobalVariable(TransferMediumName);
if (!TransferMedium) {
auto *Ty = llvm::ArrayType::get(CGM.Int64Ty, WarpSize);
unsigned SharedAddressSpace = C.getTargetAddressSpace(LangAS::cuda_shared);
TransferMedium = new llvm::GlobalVariable(
M, Ty,
/*isConstant=*/false, llvm::GlobalVariable::CommonLinkage,
llvm::Constant::getNullValue(Ty), TransferMediumName,
/*InsertBefore=*/nullptr, llvm::GlobalVariable::NotThreadLocal,
SharedAddressSpace);
}
// Get the CUDA thread id of the current OpenMP thread on the GPU.
auto *ThreadID = getNVPTXThreadID(CGF);
// nvptx_lane_id = nvptx_id % warpsize
auto *LaneID = getNVPTXLaneID(CGF);
// nvptx_warp_id = nvptx_id / warpsize
auto *WarpID = getNVPTXWarpID(CGF);
Address AddrReduceListArg = CGF.GetAddrOfLocalVar(&ReduceListArg);
Address LocalReduceList(
Bld.CreatePointerBitCastOrAddrSpaceCast(
CGF.EmitLoadOfScalar(AddrReduceListArg, /*Volatile=*/false,
C.VoidPtrTy, SourceLocation()),
CGF.ConvertTypeForMem(ReductionArrayTy)->getPointerTo()),
CGF.getPointerAlign());
unsigned Idx = 0;
for (auto &Private : Privates) {
//
// Warp master copies reduce element to transfer medium in __shared__
// memory.
//
llvm::BasicBlock *ThenBB = CGF.createBasicBlock("then");
llvm::BasicBlock *ElseBB = CGF.createBasicBlock("else");
llvm::BasicBlock *MergeBB = CGF.createBasicBlock("ifcont");
// if (lane_id == 0)
auto IsWarpMaster =
Bld.CreateICmpEQ(LaneID, Bld.getInt32(0), "warp_master");
Bld.CreateCondBr(IsWarpMaster, ThenBB, ElseBB);
CGF.EmitBlock(ThenBB);
// Reduce element = LocalReduceList[i]
Address ElemPtrPtrAddr =
Bld.CreateConstArrayGEP(LocalReduceList, Idx, CGF.getPointerSize());
llvm::Value *ElemPtrPtr = CGF.EmitLoadOfScalar(
ElemPtrPtrAddr, /*Volatile=*/false, C.VoidPtrTy, SourceLocation());
// elemptr = (type[i]*)(elemptrptr)
Address ElemPtr =
Address(ElemPtrPtr, C.getTypeAlignInChars(Private->getType()));
ElemPtr = Bld.CreateElementBitCast(
ElemPtr, CGF.ConvertTypeForMem(Private->getType()));
// elem = *elemptr
llvm::Value *Elem = CGF.EmitLoadOfScalar(
ElemPtr, /*Volatile=*/false, Private->getType(), SourceLocation());
// Get pointer to location in transfer medium.
// MediumPtr = &medium[warp_id]
llvm::Value *MediumPtrVal = Bld.CreateInBoundsGEP(
TransferMedium, {llvm::Constant::getNullValue(CGM.Int64Ty), WarpID});
Address MediumPtr(MediumPtrVal, C.getTypeAlignInChars(Private->getType()));
// Casting to actual data type.
// MediumPtr = (type[i]*)MediumPtrAddr;
MediumPtr = Bld.CreateElementBitCast(
MediumPtr, CGF.ConvertTypeForMem(Private->getType()));
//*MediumPtr = elem
Bld.CreateStore(Elem, MediumPtr);
Bld.CreateBr(MergeBB);
CGF.EmitBlock(ElseBB);
Bld.CreateBr(MergeBB);
CGF.EmitBlock(MergeBB);
Address AddrNumWarpsArg = CGF.GetAddrOfLocalVar(&NumWarpsArg);
llvm::Value *NumWarpsVal = CGF.EmitLoadOfScalar(
AddrNumWarpsArg, /*Volatile=*/false, C.IntTy, SourceLocation());
auto *NumActiveThreads = Bld.CreateNSWMul(
NumWarpsVal, getNVPTXWarpSize(CGF), "num_active_threads");
// named_barrier_sync(ParallelBarrierID, num_active_threads)
syncParallelThreads(CGF, NumActiveThreads);
//
// Warp 0 copies reduce element from transfer medium.
//
llvm::BasicBlock *W0ThenBB = CGF.createBasicBlock("then");
llvm::BasicBlock *W0ElseBB = CGF.createBasicBlock("else");
llvm::BasicBlock *W0MergeBB = CGF.createBasicBlock("ifcont");
// Up to 32 threads in warp 0 are active.
auto IsActiveThread =
Bld.CreateICmpULT(ThreadID, NumWarpsVal, "is_active_thread");
Bld.CreateCondBr(IsActiveThread, W0ThenBB, W0ElseBB);
CGF.EmitBlock(W0ThenBB);
// SrcMediumPtr = &medium[tid]
llvm::Value *SrcMediumPtrVal = Bld.CreateInBoundsGEP(
TransferMedium, {llvm::Constant::getNullValue(CGM.Int64Ty), ThreadID});
Address SrcMediumPtr(SrcMediumPtrVal,
C.getTypeAlignInChars(Private->getType()));
// SrcMediumVal = *SrcMediumPtr;
SrcMediumPtr = Bld.CreateElementBitCast(
SrcMediumPtr, CGF.ConvertTypeForMem(Private->getType()));
llvm::Value *SrcMediumValue = CGF.EmitLoadOfScalar(
SrcMediumPtr, /*Volatile=*/false, Private->getType(), SourceLocation());
// TargetElemPtr = (type[i]*)(SrcDataAddr[i])
Address TargetElemPtrPtr =
Bld.CreateConstArrayGEP(LocalReduceList, Idx, CGF.getPointerSize());
llvm::Value *TargetElemPtrVal = CGF.EmitLoadOfScalar(
TargetElemPtrPtr, /*Volatile=*/false, C.VoidPtrTy, SourceLocation());
Address TargetElemPtr =
Address(TargetElemPtrVal, C.getTypeAlignInChars(Private->getType()));
TargetElemPtr = Bld.CreateElementBitCast(
TargetElemPtr, CGF.ConvertTypeForMem(Private->getType()));
// *TargetElemPtr = SrcMediumVal;
CGF.EmitStoreOfScalar(SrcMediumValue, TargetElemPtr, /*Volatile=*/false,
Private->getType());
Bld.CreateBr(W0MergeBB);
CGF.EmitBlock(W0ElseBB);
Bld.CreateBr(W0MergeBB);
CGF.EmitBlock(W0MergeBB);
// While warp 0 copies values from transfer medium, all other warps must
// wait.
syncParallelThreads(CGF, NumActiveThreads);
Idx++;
}
CGF.FinishFunction();
return Fn;
}
/// Emit a helper that reduces data across two OpenMP threads (lanes)
/// in the same warp. It uses shuffle instructions to copy over data from
/// a remote lane's stack. The reduction algorithm performed is specified
/// by the fourth parameter.
///
/// Algorithm Versions.
/// Full Warp Reduce (argument value 0):
/// This algorithm assumes that all 32 lanes are active and gathers
/// data from these 32 lanes, producing a single resultant value.
/// Contiguous Partial Warp Reduce (argument value 1):
/// This algorithm assumes that only a *contiguous* subset of lanes
/// are active. This happens for the last warp in a parallel region
/// when the user specified num_threads is not an integer multiple of
/// 32. This contiguous subset always starts with the zeroth lane.
/// Partial Warp Reduce (argument value 2):
/// This algorithm gathers data from any number of lanes at any position.
/// All reduced values are stored in the lowest possible lane. The set
/// of problems every algorithm addresses is a super set of those
/// addressable by algorithms with a lower version number. Overhead
/// increases as algorithm version increases.
///
/// Terminology
/// Reduce element:
/// Reduce element refers to the individual data field with primitive
/// data types to be combined and reduced across threads.
/// Reduce list:
/// Reduce list refers to a collection of local, thread-private
/// reduce elements.
/// Remote Reduce list:
/// Remote Reduce list refers to a collection of remote (relative to
/// the current thread) reduce elements.
///
/// We distinguish between three states of threads that are important to
/// the implementation of this function.
/// Alive threads:
/// Threads in a warp executing the SIMT instruction, as distinguished from
/// threads that are inactive due to divergent control flow.
/// Active threads:
/// The minimal set of threads that has to be alive upon entry to this
/// function. The computation is correct iff active threads are alive.
/// Some threads are alive but they are not active because they do not
/// contribute to the computation in any useful manner. Turning them off
/// may introduce control flow overheads without any tangible benefits.
/// Effective threads:
/// In order to comply with the argument requirements of the shuffle
/// function, we must keep all lanes holding data alive. But at most
/// half of them perform value aggregation; we refer to this half of
/// threads as effective. The other half is simply handing off their
/// data.
///
/// Procedure
/// Value shuffle:
/// In this step active threads transfer data from higher lane positions
/// in the warp to lower lane positions, creating Remote Reduce list.
/// Value aggregation:
/// In this step, effective threads combine their thread local Reduce list
/// with Remote Reduce list and store the result in the thread local
/// Reduce list.
/// Value copy:
/// In this step, we deal with the assumption made by algorithm 2
/// (i.e. contiguity assumption). When we have an odd number of lanes
/// active, say 2k+1, only k threads will be effective and therefore k
/// new values will be produced. However, the Reduce list owned by the
/// (2k+1)th thread is ignored in the value aggregation. Therefore
/// we copy the Reduce list from the (2k+1)th lane to (k+1)th lane so
/// that the contiguity assumption still holds.
static llvm::Value *
emitShuffleAndReduceFunction(CodeGenModule &CGM,
ArrayRef<const Expr *> Privates,
QualType ReductionArrayTy, llvm::Value *ReduceFn) {
auto &C = CGM.getContext();
// Thread local Reduce list used to host the values of data to be reduced.
ImplicitParamDecl ReduceListArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, C.VoidPtrTy);
// Current lane id; could be logical.
ImplicitParamDecl LaneIDArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, C.ShortTy);
// Offset of the remote source lane relative to the current lane.
ImplicitParamDecl RemoteLaneOffsetArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, C.ShortTy);
// Algorithm version. This is expected to be known at compile time.
ImplicitParamDecl AlgoVerArg(C, /*DC=*/nullptr, SourceLocation(),
/*Id=*/nullptr, C.ShortTy);
FunctionArgList Args;
Args.push_back(&ReduceListArg);
Args.push_back(&LaneIDArg);
Args.push_back(&RemoteLaneOffsetArg);
Args.push_back(&AlgoVerArg);
auto &CGFI = CGM.getTypes().arrangeBuiltinFunctionDeclaration(C.VoidTy, Args);
auto *Fn = llvm::Function::Create(
CGM.getTypes().GetFunctionType(CGFI), llvm::GlobalValue::InternalLinkage,
"_omp_reduction_shuffle_and_reduce_func", &CGM.getModule());
CGM.SetInternalFunctionAttributes(/*D=*/nullptr, Fn, CGFI);
CodeGenFunction CGF(CGM);
// We don't need debug information in this function as nothing here refers to
// user code.
CGF.disableDebugInfo();
CGF.StartFunction(GlobalDecl(), C.VoidTy, Fn, CGFI, Args);
auto &Bld = CGF.Builder;
Address AddrReduceListArg = CGF.GetAddrOfLocalVar(&ReduceListArg);
Address LocalReduceList(
Bld.CreatePointerBitCastOrAddrSpaceCast(
CGF.EmitLoadOfScalar(AddrReduceListArg, /*Volatile=*/false,
C.VoidPtrTy, SourceLocation()),
CGF.ConvertTypeForMem(ReductionArrayTy)->getPointerTo()),
CGF.getPointerAlign());
Address AddrLaneIDArg = CGF.GetAddrOfLocalVar(&LaneIDArg);
llvm::Value *LaneIDArgVal = CGF.EmitLoadOfScalar(
AddrLaneIDArg, /*Volatile=*/false, C.ShortTy, SourceLocation());
Address AddrRemoteLaneOffsetArg = CGF.GetAddrOfLocalVar(&RemoteLaneOffsetArg);
llvm::Value *RemoteLaneOffsetArgVal = CGF.EmitLoadOfScalar(
AddrRemoteLaneOffsetArg, /*Volatile=*/false, C.ShortTy, SourceLocation());
Address AddrAlgoVerArg = CGF.GetAddrOfLocalVar(&AlgoVerArg);
llvm::Value *AlgoVerArgVal = CGF.EmitLoadOfScalar(
AddrAlgoVerArg, /*Volatile=*/false, C.ShortTy, SourceLocation());
// Create a local thread-private variable to host the Reduce list
// from a remote lane.
Address RemoteReduceList =
CGF.CreateMemTemp(ReductionArrayTy, ".omp.reduction.remote_reduce_list");
// This loop iterates through the list of reduce elements and copies,
// element by element, from a remote lane in the warp to RemoteReduceList,
// hosted on the thread's stack.
emitReductionListCopy(RemoteLaneToThread, CGF, ReductionArrayTy, Privates,
LocalReduceList, RemoteReduceList,
{/*RemoteLaneOffset=*/RemoteLaneOffsetArgVal,
/*ScratchpadIndex=*/nullptr,
/*ScratchpadWidth=*/nullptr});
// The actions to be performed on the Remote Reduce list is dependent
// on the algorithm version.
//
// if (AlgoVer==0) || (AlgoVer==1 && (LaneId < Offset)) || (AlgoVer==2 &&
// LaneId % 2 == 0 && Offset > 0):
// do the reduction value aggregation
//
// The thread local variable Reduce list is mutated in place to host the
// reduced data, which is the aggregated value produced from local and
// remote lanes.
//
// Note that AlgoVer is expected to be a constant integer known at compile
// time.
// When AlgoVer==0, the first conjunction evaluates to true, making
// the entire predicate true during compile time.
// When AlgoVer==1, the second conjunction has only the second part to be
// evaluated during runtime. Other conjunctions evaluates to false
// during compile time.
// When AlgoVer==2, the third conjunction has only the second part to be
// evaluated during runtime. Other conjunctions evaluates to false
// during compile time.
auto CondAlgo0 = Bld.CreateICmpEQ(AlgoVerArgVal, Bld.getInt16(0));
auto Algo1 = Bld.CreateICmpEQ(AlgoVerArgVal, Bld.getInt16(1));
auto CondAlgo1 = Bld.CreateAnd(
Algo1, Bld.CreateICmpULT(LaneIDArgVal, RemoteLaneOffsetArgVal));
auto Algo2 = Bld.CreateICmpEQ(AlgoVerArgVal, Bld.getInt16(2));
auto CondAlgo2 = Bld.CreateAnd(
Algo2,
Bld.CreateICmpEQ(Bld.CreateAnd(LaneIDArgVal, Bld.getInt16(1)),
Bld.getInt16(0)));
CondAlgo2 = Bld.CreateAnd(
CondAlgo2, Bld.CreateICmpSGT(RemoteLaneOffsetArgVal, Bld.getInt16(0)));
auto CondReduce = Bld.CreateOr(CondAlgo0, CondAlgo1);
CondReduce = Bld.CreateOr(CondReduce, CondAlgo2);
llvm::BasicBlock *ThenBB = CGF.createBasicBlock("then");
llvm::BasicBlock *ElseBB = CGF.createBasicBlock("else");
llvm::BasicBlock *MergeBB = CGF.createBasicBlock("ifcont");
Bld.CreateCondBr(CondReduce, ThenBB, ElseBB);
CGF.EmitBlock(ThenBB);
// reduce_function(LocalReduceList, RemoteReduceList)
llvm::Value *LocalReduceListPtr = Bld.CreatePointerBitCastOrAddrSpaceCast(
LocalReduceList.getPointer(), CGF.VoidPtrTy);
llvm::Value *RemoteReduceListPtr = Bld.CreatePointerBitCastOrAddrSpaceCast(
RemoteReduceList.getPointer(), CGF.VoidPtrTy);
CGF.EmitCallOrInvoke(ReduceFn, {LocalReduceListPtr, RemoteReduceListPtr});
Bld.CreateBr(MergeBB);
CGF.EmitBlock(ElseBB);
Bld.CreateBr(MergeBB);
CGF.EmitBlock(MergeBB);
// if (AlgoVer==1 && (LaneId >= Offset)) copy Remote Reduce list to local
// Reduce list.
Algo1 = Bld.CreateICmpEQ(AlgoVerArgVal, Bld.getInt16(1));
auto CondCopy = Bld.CreateAnd(
Algo1, Bld.CreateICmpUGE(LaneIDArgVal, RemoteLaneOffsetArgVal));
llvm::BasicBlock *CpyThenBB = CGF.createBasicBlock("then");
llvm::BasicBlock *CpyElseBB = CGF.createBasicBlock("else");
llvm::BasicBlock *CpyMergeBB = CGF.createBasicBlock("ifcont");
Bld.CreateCondBr(CondCopy, CpyThenBB, CpyElseBB);
CGF.EmitBlock(CpyThenBB);
emitReductionListCopy(ThreadCopy, CGF, ReductionArrayTy, Privates,
RemoteReduceList, LocalReduceList);
Bld.CreateBr(CpyMergeBB);
CGF.EmitBlock(CpyElseBB);
Bld.CreateBr(CpyMergeBB);
CGF.EmitBlock(CpyMergeBB);
CGF.FinishFunction();
return Fn;
}
///
/// Design of OpenMP reductions on the GPU
///
/// Consider a typical OpenMP program with one or more reduction
/// clauses:
///
/// float foo;
/// double bar;
/// #pragma omp target teams distribute parallel for \
/// reduction(+:foo) reduction(*:bar)
/// for (int i = 0; i < N; i++) {
/// foo += A[i]; bar *= B[i];
/// }
///
/// where 'foo' and 'bar' are reduced across all OpenMP threads in
/// all teams. In our OpenMP implementation on the NVPTX device an
/// OpenMP team is mapped to a CUDA threadblock and OpenMP threads
/// within a team are mapped to CUDA threads within a threadblock.
/// Our goal is to efficiently aggregate values across all OpenMP
/// threads such that:
///
/// - the compiler and runtime are logically concise, and
/// - the reduction is performed efficiently in a hierarchical
/// manner as follows: within OpenMP threads in the same warp,
/// across warps in a threadblock, and finally across teams on
/// the NVPTX device.
///
/// Introduction to Decoupling
///
/// We would like to decouple the compiler and the runtime so that the
/// latter is ignorant of the reduction variables (number, data types)
/// and the reduction operators. This allows a simpler interface
/// and implementation while still attaining good performance.
///
/// Pseudocode for the aforementioned OpenMP program generated by the
/// compiler is as follows:
///
/// 1. Create private copies of reduction variables on each OpenMP
/// thread: 'foo_private', 'bar_private'
/// 2. Each OpenMP thread reduces the chunk of 'A' and 'B' assigned
/// to it and writes the result in 'foo_private' and 'bar_private'
/// respectively.
/// 3. Call the OpenMP runtime on the GPU to reduce within a team
/// and store the result on the team master:
///
/// __kmpc_nvptx_parallel_reduce_nowait(...,
/// reduceData, shuffleReduceFn, interWarpCpyFn)
///
/// where:
/// struct ReduceData {
/// double *foo;
/// double *bar;
/// } reduceData
/// reduceData.foo = &foo_private
/// reduceData.bar = &bar_private
///
/// 'shuffleReduceFn' and 'interWarpCpyFn' are pointers to two
/// auxiliary functions generated by the compiler that operate on
/// variables of type 'ReduceData'. They aid the runtime perform
/// algorithmic steps in a data agnostic manner.
///
/// 'shuffleReduceFn' is a pointer to a function that reduces data
/// of type 'ReduceData' across two OpenMP threads (lanes) in the
/// same warp. It takes the following arguments as input:
///
/// a. variable of type 'ReduceData' on the calling lane,
/// b. its lane_id,
/// c. an offset relative to the current lane_id to generate a
/// remote_lane_id. The remote lane contains the second
/// variable of type 'ReduceData' that is to be reduced.
/// d. an algorithm version parameter determining which reduction
/// algorithm to use.
///
/// 'shuffleReduceFn' retrieves data from the remote lane using
/// efficient GPU shuffle intrinsics and reduces, using the
/// algorithm specified by the 4th parameter, the two operands
/// element-wise. The result is written to the first operand.
///
/// Different reduction algorithms are implemented in different
/// runtime functions, all calling 'shuffleReduceFn' to perform
/// the essential reduction step. Therefore, based on the 4th
/// parameter, this function behaves slightly differently to
/// cooperate with the runtime to ensure correctness under
/// different circumstances.
///
/// 'InterWarpCpyFn' is a pointer to a function that transfers
/// reduced variables across warps. It tunnels, through CUDA
/// shared memory, the thread-private data of type 'ReduceData'
/// from lane 0 of each warp to a lane in the first warp.
/// 4. Call the OpenMP runtime on the GPU to reduce across teams.
/// The last team writes the global reduced value to memory.
///
/// ret = __kmpc_nvptx_teams_reduce_nowait(...,
/// reduceData, shuffleReduceFn, interWarpCpyFn,
/// scratchpadCopyFn, loadAndReduceFn)
///
/// 'scratchpadCopyFn' is a helper that stores reduced
/// data from the team master to a scratchpad array in
/// global memory.
///
/// 'loadAndReduceFn' is a helper that loads data from
/// the scratchpad array and reduces it with the input
/// operand.
///
/// These compiler generated functions hide address
/// calculation and alignment information from the runtime.
/// 5. if ret == 1:
/// The team master of the last team stores the reduced
/// result to the globals in memory.
/// foo += reduceData.foo; bar *= reduceData.bar
///
///
/// Warp Reduction Algorithms
///
/// On the warp level, we have three algorithms implemented in the
/// OpenMP runtime depending on the number of active lanes:
///
/// Full Warp Reduction
///
/// The reduce algorithm within a warp where all lanes are active
/// is implemented in the runtime as follows:
///
/// full_warp_reduce(void *reduce_data,
/// kmp_ShuffleReductFctPtr ShuffleReduceFn) {
/// for (int offset = WARPSIZE/2; offset > 0; offset /= 2)
/// ShuffleReduceFn(reduce_data, 0, offset, 0);
/// }
///
/// The algorithm completes in log(2, WARPSIZE) steps.
///
/// 'ShuffleReduceFn' is used here with lane_id set to 0 because it is
/// not used therefore we save instructions by not retrieving lane_id
/// from the corresponding special registers. The 4th parameter, which
/// represents the version of the algorithm being used, is set to 0 to
/// signify full warp reduction.
///
/// In this version, 'ShuffleReduceFn' behaves, per element, as follows:
///
/// #reduce_elem refers to an element in the local lane's data structure
/// #remote_elem is retrieved from a remote lane
/// remote_elem = shuffle_down(reduce_elem, offset, WARPSIZE);
/// reduce_elem = reduce_elem REDUCE_OP remote_elem;
///
/// Contiguous Partial Warp Reduction
///
/// This reduce algorithm is used within a warp where only the first
/// 'n' (n <= WARPSIZE) lanes are active. It is typically used when the
/// number of OpenMP threads in a parallel region is not a multiple of
/// WARPSIZE. The algorithm is implemented in the runtime as follows:
///
/// void
/// contiguous_partial_reduce(void *reduce_data,
/// kmp_ShuffleReductFctPtr ShuffleReduceFn,
/// int size, int lane_id) {
/// int curr_size;
/// int offset;
/// curr_size = size;
/// mask = curr_size/2;
/// while (offset>0) {
/// ShuffleReduceFn(reduce_data, lane_id, offset, 1);
/// curr_size = (curr_size+1)/2;
/// offset = curr_size/2;
/// }
/// }
///
/// In this version, 'ShuffleReduceFn' behaves, per element, as follows:
///
/// remote_elem = shuffle_down(reduce_elem, offset, WARPSIZE);
/// if (lane_id < offset)
/// reduce_elem = reduce_elem REDUCE_OP remote_elem
/// else
/// reduce_elem = remote_elem
///
/// This algorithm assumes that the data to be reduced are located in a
/// contiguous subset of lanes starting from the first. When there is
/// an odd number of active lanes, the data in the last lane is not
/// aggregated with any other lane's dat but is instead copied over.
///
/// Dispersed Partial Warp Reduction
///
/// This algorithm is used within a warp when any discontiguous subset of
/// lanes are active. It is used to implement the reduction operation
/// across lanes in an OpenMP simd region or in a nested parallel region.
///
/// void
/// dispersed_partial_reduce(void *reduce_data,
/// kmp_ShuffleReductFctPtr ShuffleReduceFn) {
/// int size, remote_id;
/// int logical_lane_id = number_of_active_lanes_before_me() * 2;
/// do {
/// remote_id = next_active_lane_id_right_after_me();
/// # the above function returns 0 of no active lane
/// # is present right after the current lane.
/// size = number_of_active_lanes_in_this_warp();
/// logical_lane_id /= 2;
/// ShuffleReduceFn(reduce_data, logical_lane_id,
/// remote_id-1-threadIdx.x, 2);
/// } while (logical_lane_id % 2 == 0 && size > 1);
/// }
///
/// There is no assumption made about the initial state of the reduction.
/// Any number of lanes (>=1) could be active at any position. The reduction
/// result is returned in the first active lane.
///
/// In this version, 'ShuffleReduceFn' behaves, per element, as follows:
///
/// remote_elem = shuffle_down(reduce_elem, offset, WARPSIZE);
/// if (lane_id % 2 == 0 && offset > 0)
/// reduce_elem = reduce_elem REDUCE_OP remote_elem
/// else
/// reduce_elem = remote_elem
///
///
/// Intra-Team Reduction
///
/// This function, as implemented in the runtime call
/// '__kmpc_nvptx_parallel_reduce_nowait', aggregates data across OpenMP
/// threads in a team. It first reduces within a warp using the
/// aforementioned algorithms. We then proceed to gather all such
/// reduced values at the first warp.
///
/// The runtime makes use of the function 'InterWarpCpyFn', which copies
/// data from each of the "warp master" (zeroth lane of each warp, where
/// warp-reduced data is held) to the zeroth warp. This step reduces (in
/// a mathematical sense) the problem of reduction across warp masters in
/// a block to the problem of warp reduction.
///
///
/// Inter-Team Reduction
///
/// Once a team has reduced its data to a single value, it is stored in
/// a global scratchpad array. Since each team has a distinct slot, this
/// can be done without locking.
///
/// The last team to write to the scratchpad array proceeds to reduce the
/// scratchpad array. One or more workers in the last team use the helper
/// 'loadAndReduceDataFn' to load and reduce values from the array, i.e.,
/// the k'th worker reduces every k'th element.
///
/// Finally, a call is made to '__kmpc_nvptx_parallel_reduce_nowait' to
/// reduce across workers and compute a globally reduced value.
///
void CGOpenMPRuntimeNVPTX::emitReduction(
CodeGenFunction &CGF, SourceLocation Loc, ArrayRef<const Expr *> Privates,
ArrayRef<const Expr *> LHSExprs, ArrayRef<const Expr *> RHSExprs,
ArrayRef<const Expr *> ReductionOps, ReductionOptionsTy Options) {
if (!CGF.HaveInsertPoint())
return;
bool ParallelReduction = isOpenMPParallelDirective(Options.ReductionKind);
bool TeamsReduction = isOpenMPTeamsDirective(Options.ReductionKind);
// FIXME: Add support for simd reduction.
assert((TeamsReduction || ParallelReduction) &&
"Invalid reduction selection in emitReduction.");
auto &C = CGM.getContext();
// 1. Build a list of reduction variables.
// void *RedList[<n>] = {<ReductionVars>[0], ..., <ReductionVars>[<n>-1]};
auto Size = RHSExprs.size();
for (auto *E : Privates) {
if (E->getType()->isVariablyModifiedType())
// Reserve place for array size.
++Size;
}
llvm::APInt ArraySize(/*unsigned int numBits=*/32, Size);
QualType ReductionArrayTy =
C.getConstantArrayType(C.VoidPtrTy, ArraySize, ArrayType::Normal,
/*IndexTypeQuals=*/0);
Address ReductionList =
CGF.CreateMemTemp(ReductionArrayTy, ".omp.reduction.red_list");
auto IPriv = Privates.begin();
unsigned Idx = 0;
for (unsigned I = 0, E = RHSExprs.size(); I < E; ++I, ++IPriv, ++Idx) {
Address Elem = CGF.Builder.CreateConstArrayGEP(ReductionList, Idx,
CGF.getPointerSize());
CGF.Builder.CreateStore(
CGF.Builder.CreatePointerBitCastOrAddrSpaceCast(
CGF.EmitLValue(RHSExprs[I]).getPointer(), CGF.VoidPtrTy),
Elem);
if ((*IPriv)->getType()->isVariablyModifiedType()) {
// Store array size.
++Idx;
Elem = CGF.Builder.CreateConstArrayGEP(ReductionList, Idx,
CGF.getPointerSize());
llvm::Value *Size = CGF.Builder.CreateIntCast(
CGF.getVLASize(
CGF.getContext().getAsVariableArrayType((*IPriv)->getType()))
.first,
CGF.SizeTy, /*isSigned=*/false);
CGF.Builder.CreateStore(CGF.Builder.CreateIntToPtr(Size, CGF.VoidPtrTy),
Elem);
}
}
// 2. Emit reduce_func().
auto *ReductionFn = emitReductionFunction(
CGM, CGF.ConvertTypeForMem(ReductionArrayTy)->getPointerTo(), Privates,
LHSExprs, RHSExprs, ReductionOps);
// 4. Build res = __kmpc_reduce{_nowait}(<gtid>, <n>, sizeof(RedList),
// RedList, shuffle_reduce_func, interwarp_copy_func);
auto *ThreadId = getThreadID(CGF, Loc);
auto *ReductionArrayTySize = CGF.getTypeSize(ReductionArrayTy);
auto *RL = CGF.Builder.CreatePointerBitCastOrAddrSpaceCast(
ReductionList.getPointer(), CGF.VoidPtrTy);
auto *ShuffleAndReduceFn = emitShuffleAndReduceFunction(
CGM, Privates, ReductionArrayTy, ReductionFn);
auto *InterWarpCopyFn =
emitInterWarpCopyFunction(CGM, Privates, ReductionArrayTy);
llvm::Value *Res = nullptr;
if (ParallelReduction) {
llvm::Value *Args[] = {ThreadId,
CGF.Builder.getInt32(RHSExprs.size()),
ReductionArrayTySize,
RL,
ShuffleAndReduceFn,
InterWarpCopyFn};
Res = CGF.EmitRuntimeCall(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_parallel_reduce_nowait),
Args);
}
if (TeamsReduction) {
auto *ScratchPadCopyFn =
emitCopyToScratchpad(CGM, Privates, ReductionArrayTy);
auto *LoadAndReduceFn = emitReduceScratchpadFunction(
CGM, Privates, ReductionArrayTy, ReductionFn);
llvm::Value *Args[] = {ThreadId,
CGF.Builder.getInt32(RHSExprs.size()),
ReductionArrayTySize,
RL,
ShuffleAndReduceFn,
InterWarpCopyFn,
ScratchPadCopyFn,
LoadAndReduceFn};
Res = CGF.EmitRuntimeCall(
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_teams_reduce_nowait),
Args);
}
// 5. Build switch(res)
auto *DefaultBB = CGF.createBasicBlock(".omp.reduction.default");
auto *SwInst = CGF.Builder.CreateSwitch(Res, DefaultBB, /*NumCases=*/1);
// 6. Build case 1: where we have reduced values in the master
// thread in each team.
// __kmpc_end_reduce{_nowait}(<gtid>);
// break;
auto *Case1BB = CGF.createBasicBlock(".omp.reduction.case1");
SwInst->addCase(CGF.Builder.getInt32(1), Case1BB);
CGF.EmitBlock(Case1BB);
// Add emission of __kmpc_end_reduce{_nowait}(<gtid>);
llvm::Value *EndArgs[] = {ThreadId};
auto &&CodeGen = [&Privates, &LHSExprs, &RHSExprs, &ReductionOps,
this](CodeGenFunction &CGF, PrePostActionTy &Action) {
auto IPriv = Privates.begin();
auto ILHS = LHSExprs.begin();
auto IRHS = RHSExprs.begin();
for (auto *E : ReductionOps) {
emitSingleReductionCombiner(CGF, E, *IPriv, cast<DeclRefExpr>(*ILHS),
cast<DeclRefExpr>(*IRHS));
++IPriv;
++ILHS;
++IRHS;
}
};
RegionCodeGenTy RCG(CodeGen);
NVPTXActionTy Action(
nullptr, llvm::None,
createNVPTXRuntimeFunction(OMPRTL_NVPTX__kmpc_end_reduce_nowait),
EndArgs);
RCG.setAction(Action);
RCG(CGF);
CGF.EmitBranch(DefaultBB);
CGF.EmitBlock(DefaultBB, /*IsFinished=*/true);
}
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