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[libomptarget][NFC] Outline parallel SPMD function #78642

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Jan 29, 2024
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[libomptarget][NFC] Outline parallel SPMD function #78642

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108 changes: 62 additions & 46 deletions openmp/libomptarget/DeviceRTL/src/Parallelism.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -83,6 +83,64 @@ uint32_t determineNumberOfThreads(int32_t NumThreadsClause) {

extern "C" {

[[clang::always_inline]] void __kmpc_parallel_spmd(IdentTy *ident,
int32_t num_threads,
void *fn, void **args,
const int64_t nargs) {
uint32_t TId = mapping::getThreadIdInBlock();
uint32_t NumThreads = determineNumberOfThreads(num_threads);
uint32_t PTeamSize =
NumThreads == mapping::getMaxTeamThreads() ? 0 : NumThreads;
// Avoid the race between the read of the `icv::Level` above and the write
// below by synchronizing all threads here.
synchronize::threadsAligned(atomic::seq_cst);
{
// Note that the order here is important. `icv::Level` has to be updated
// last or the other updates will cause a thread specific state to be
// created.
state::ValueRAII ParallelTeamSizeRAII(state::ParallelTeamSize, PTeamSize,
1u, TId == 0, ident,
/*ForceTeamState=*/true);
state::ValueRAII ActiveLevelRAII(icv::ActiveLevel, 1u, 0u, TId == 0, ident,
/*ForceTeamState=*/true);
state::ValueRAII LevelRAII(icv::Level, 1u, 0u, TId == 0, ident,
/*ForceTeamState=*/true);

// Synchronize all threads after the main thread (TId == 0) set up the
// team state properly.
synchronize::threadsAligned(atomic::acq_rel);

state::ParallelTeamSize.assert_eq(PTeamSize, ident,
/*ForceTeamState=*/true);
icv::ActiveLevel.assert_eq(1u, ident, /*ForceTeamState=*/true);
icv::Level.assert_eq(1u, ident, /*ForceTeamState=*/true);

// Ensure we synchronize before we run user code to avoid invalidating the
// assumptions above.
synchronize::threadsAligned(atomic::relaxed);

if (!PTeamSize || TId < PTeamSize)
invokeMicrotask(TId, 0, fn, args, nargs);

// Synchronize all threads at the end of a parallel region.
synchronize::threadsAligned(atomic::seq_cst);
}

// Synchronize all threads to make sure every thread exits the scope above;
// otherwise the following assertions and the assumption in
// __kmpc_target_deinit may not hold.
synchronize::threadsAligned(atomic::acq_rel);

state::ParallelTeamSize.assert_eq(1u, ident, /*ForceTeamState=*/true);
icv::ActiveLevel.assert_eq(0u, ident, /*ForceTeamState=*/true);
icv::Level.assert_eq(0u, ident, /*ForceTeamState=*/true);

// Ensure we synchronize to create an aligned region around the assumptions.
synchronize::threadsAligned(atomic::relaxed);

return;
}

[[clang::always_inline]] void
__kmpc_parallel_51(IdentTy *ident, int32_t, int32_t if_expr,
int32_t num_threads, int proc_bind, void *fn,
Expand Down Expand Up @@ -112,52 +170,10 @@ __kmpc_parallel_51(IdentTy *ident, int32_t, int32_t if_expr,
uint32_t MaxTeamThreads = mapping::getMaxTeamThreads();
uint32_t PTeamSize = NumThreads == MaxTeamThreads ? 0 : NumThreads;
if (mapping::isSPMDMode()) {
// Avoid the race between the read of the `icv::Level` above and the write
// below by synchronizing all threads here.
synchronize::threadsAligned(atomic::seq_cst);
{
// Note that the order here is important. `icv::Level` has to be updated
// last or the other updates will cause a thread specific state to be
// created.
state::ValueRAII ParallelTeamSizeRAII(state::ParallelTeamSize, PTeamSize,
1u, TId == 0, ident,
/*ForceTeamState=*/true);
state::ValueRAII ActiveLevelRAII(icv::ActiveLevel, 1u, 0u, TId == 0,
ident, /*ForceTeamState=*/true);
state::ValueRAII LevelRAII(icv::Level, 1u, 0u, TId == 0, ident,
/*ForceTeamState=*/true);

// Synchronize all threads after the main thread (TId == 0) set up the
// team state properly.
synchronize::threadsAligned(atomic::acq_rel);

state::ParallelTeamSize.assert_eq(PTeamSize, ident,
/*ForceTeamState=*/true);
icv::ActiveLevel.assert_eq(1u, ident, /*ForceTeamState=*/true);
icv::Level.assert_eq(1u, ident, /*ForceTeamState=*/true);

// Ensure we synchronize before we run user code to avoid invalidating the
// assumptions above.
synchronize::threadsAligned(atomic::relaxed);

if (!PTeamSize || TId < PTeamSize)
invokeMicrotask(TId, 0, fn, args, nargs);

// Synchronize all threads at the end of a parallel region.
synchronize::threadsAligned(atomic::seq_cst);
}

// Synchronize all threads to make sure every thread exits the scope above;
// otherwise the following assertions and the assumption in
// __kmpc_target_deinit may not hold.
synchronize::threadsAligned(atomic::acq_rel);

state::ParallelTeamSize.assert_eq(1u, ident, /*ForceTeamState=*/true);
icv::ActiveLevel.assert_eq(0u, ident, /*ForceTeamState=*/true);
icv::Level.assert_eq(0u, ident, /*ForceTeamState=*/true);

// Ensure we synchronize to create an aligned region around the assumptions.
synchronize::threadsAligned(atomic::relaxed);
// This was moved to its own routine so it could be called directly
// in certain situations to avoid resource consumption of unused
// logic in parallel_51.
__kmpc_parallel_spmd(ident, num_threads, fn, args, nargs);

return;
}
Expand Down