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[OPENMP][NVPTX]Fix incompatibility of __syncthreads with LLVM, NFC.

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Summary:
One of the LLVM optimizations, split critical edges, also clones tail
instructions. This is a dangerous operation for __syncthreads()
functions and this transformation leads to undefined behavior or
incorrect results. Patch fixes this problem by replacing __syncthreads()
function with the assembler instruction, which cost is too high and
wich cannot be copied.

Reviewers: grokos, gtbercea, kkwli0

Subscribers: guansong, openmp-commits, caomhin

Differential Revision: https://reviews.llvm.org/D56274

llvm-svn: 350333
This commit is contained in:
Alexey Bataev 2019-01-03 17:43:46 +00:00
parent 0f67746c92
commit 3c74be8049
4 changed files with 15 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
openmp/libomptarget/deviceRTLs/nvptx/src/data_sharing.cu
View File

@ -564,7 +564,8 @@ EXTERN void __kmpc_get_team_static_memory(const void *buf, size_t size,
if (GetThreadIdInBlock() == 0) {
*frame = omptarget_nvptx_simpleMemoryManager.Acquire(buf, size);
}
__syncthreads();
// FIXME: use __syncthreads instead when the function copy is fixed in LLVM.
__SYNCTHREADS();
return;
}
ASSERT0(LT_FUSSY, GetThreadIdInBlock() == getMasterThreadId(),
@ -577,7 +578,8 @@ EXTERN void __kmpc_restore_team_static_memory(int16_t is_shared) {
if (is_shared)
return;
if (isSPMDMode()) {
__syncthreads();
// FIXME: use __syncthreads instead when the function copy is fixed in LLVM.
__SYNCTHREADS();
if (GetThreadIdInBlock() == 0) {
omptarget_nvptx_simpleMemoryManager.Release();
}

9
openmp/libomptarget/deviceRTLs/nvptx/src/omptarget-nvptx.cu
View File

@ -105,7 +105,8 @@ EXTERN void __kmpc_spmd_kernel_init(int ThreadLimit, int16_t RequiresOMPRuntime,
omptarget_nvptx_simpleThreadPrivateContext =
omptarget_nvptx_device_simpleState[slot].Dequeue();
}
__syncthreads();
// FIXME: use __syncthreads instead when the function copy is fixed in LLVM.
__SYNCTHREADS();
omptarget_nvptx_simpleThreadPrivateContext->Init();
return;
}
@ -129,7 +130,8 @@ EXTERN void __kmpc_spmd_kernel_init(int ThreadLimit, int16_t RequiresOMPRuntime,
// init team context
currTeamDescr.InitTeamDescr();
}
__syncthreads();
// FIXME: use __syncthreads instead when the function copy is fixed in LLVM.
__SYNCTHREADS();
omptarget_nvptx_TeamDescr &currTeamDescr = getMyTeamDescriptor();
omptarget_nvptx_WorkDescr &workDescr = getMyWorkDescriptor();
@ -170,7 +172,8 @@ EXTERN __attribute__((deprecated)) void __kmpc_spmd_kernel_deinit() {
EXTERN void __kmpc_spmd_kernel_deinit_v2(int16_t RequiresOMPRuntime) {
// We're not going to pop the task descr stack of each thread since
// there are no more parallel regions in SPMD mode.
__syncthreads();
// FIXME: use __syncthreads instead when the function copy is fixed in LLVM.
__SYNCTHREADS();
int threadId = GetThreadIdInBlock();
if (!RequiresOMPRuntime) {
if (threadId == 0) {

3
openmp/libomptarget/deviceRTLs/nvptx/src/omptarget-nvptx.h
View File

@ -63,6 +63,9 @@
#define __ACTIVEMASK() __ballot(1)
#endif
#define __SYNCTHREADS_N(n) asm volatile("bar.sync %0;" : : "r"(n) : "memory");
#define __SYNCTHREADS() __SYNCTHREADS_N(0)
// arguments needed for L0 parallelism only.
class omptarget_nvptx_SharedArgs {
public:

3
openmp/libomptarget/deviceRTLs/nvptx/src/sync.cu
View File

@ -74,7 +74,8 @@ EXTERN void __kmpc_barrier(kmp_Ident *loc_ref, int32_t tid) {
// parallel region and that all worker threads participate.
EXTERN void __kmpc_barrier_simple_spmd(kmp_Ident *loc_ref, int32_t tid) {
PRINT0(LD_SYNC, "call kmpc_barrier_simple_spmd\n");
__syncthreads();
// FIXME: use __syncthreads instead when the function copy is fixed in LLVM.
__SYNCTHREADS();
PRINT0(LD_SYNC, "completed kmpc_barrier_simple_spmd\n");
}