[Openmp-commits] [PATCH] D62199: [OPENMP][NVPTX]Fix barriers and parallel level counters, NFC.

[Alexey Bataev via Phabricator via Openmp-commits]

ABataev created this revision.
ABataev added reviewers: gtbercea, kkwli0, grokos.
Herald added subscribers: jdoerfert, jfb, guansong.
Herald added a project: OpenMP.

Parallel level counter should be volatile to prevent some dangerous
optimiations by the ptxas. Otherwise, ptxas optimizations lead to
undefined behaviour in some cases.
Also, use __threadfence() for #pragma omp flush and if the barrier
should not be used (we have only one thread in the team), still perform
flush operation since the standard requires implicit flush when
executing barriers.


Repository:
  rOMP OpenMP

https://reviews.llvm.org/D62199

Files:
  libomptarget/deviceRTLs/nvptx/src/omp_data.cu
  libomptarget/deviceRTLs/nvptx/src/omptarget-nvptx.h
  libomptarget/deviceRTLs/nvptx/src/sync.cu


Index: libomptarget/deviceRTLs/nvptx/src/sync.cu
===================================================================
--- libomptarget/deviceRTLs/nvptx/src/sync.cu
+++ libomptarget/deviceRTLs/nvptx/src/sync.cu
@@ -62,6 +62,8 @@
         // Barrier #1 is for synchronization among active threads.
         named_sync(L1_BARRIER, threads);
       }
+    } else {
+      __kmpc_flush(loc_ref);
     } // numberOfActiveOMPThreads > 1
     PRINT0(LD_SYNC, "completed kmpc_barrier\n");
   }
@@ -130,7 +132,7 @@
 
 EXTERN void __kmpc_flush(kmp_Ident *loc) {
   PRINT0(LD_IO, "call kmpc_flush\n");
-  __threadfence_system();
+  __threadfence();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
Index: libomptarget/deviceRTLs/nvptx/src/omptarget-nvptx.h
===================================================================
--- libomptarget/deviceRTLs/nvptx/src/omptarget-nvptx.h
+++ libomptarget/deviceRTLs/nvptx/src/omptarget-nvptx.h
@@ -398,7 +398,7 @@
     omptarget_nvptx_simpleMemoryManager;
 extern __device__ __shared__ uint32_t usedMemIdx;
 extern __device__ __shared__ uint32_t usedSlotIdx;
-extern __device__ __shared__ uint8_t
+extern __device__ __shared__ volatile uint8_t
     parallelLevel[MAX_THREADS_PER_TEAM / WARPSIZE];
 extern __device__ __shared__ uint16_t threadLimit;
 extern __device__ __shared__ uint16_t threadsInTeam;
Index: libomptarget/deviceRTLs/nvptx/src/omp_data.cu
===================================================================
--- libomptarget/deviceRTLs/nvptx/src/omp_data.cu
+++ libomptarget/deviceRTLs/nvptx/src/omp_data.cu
@@ -31,7 +31,8 @@
 __device__ __shared__ uint32_t usedMemIdx;
 __device__ __shared__ uint32_t usedSlotIdx;
 
-__device__ __shared__ uint8_t parallelLevel[MAX_THREADS_PER_TEAM / WARPSIZE];
+__device__ __shared__ volatile uint8_t
+    parallelLevel[MAX_THREADS_PER_TEAM / WARPSIZE];
 __device__ __shared__ uint16_t threadLimit;
 __device__ __shared__ uint16_t threadsInTeam;
 __device__ __shared__ uint16_t nThreads;


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