[OpenMP][libomptarget] Initialize global memory stack only once.

Summary: The global stack initialization function may be called multiple times. The initialization of the shared memory slots should only happen when the function is called for the first time for a given warp master thread.

Reviewers: grokos, carlo.bertolli, ABataev, caomhin

Reviewed By: grokos

Subscribers: guansong, openmp-commits

Differential Revision: https://reviews.llvm.org/D44754

llvm-svn: 328148

openmp/libomptarget/deviceRTLs/nvptx/src/data_sharing.cu

@@ -346,9 +346,14 @@ EXTERN void __kmpc_data_sharing_init_stack() {
         &omptarget_nvptx_threadPrivateContext->TeamContext();
     __kmpc_data_sharing_slot *RootS = teamDescr->RootS(WID, IsMasterThread());
 
-    DataSharingState.SlotPtr[WID] = RootS;
-    DataSharingState.TailPtr[WID] = RootS;
-    DataSharingState.StackPtr[WID] = (void *)&RootS->Data[0];
+    // If a valid address has been returned then proceed with the initalization.
+    // Otherwise the initialization of the slot has already happened in a
+    // previous call to this function.
+    if (RootS) {
+      DataSharingState.SlotPtr[WID] = RootS;
+      DataSharingState.TailPtr[WID] = RootS;
+      DataSharingState.StackPtr[WID] = (void *)&RootS->Data[0];
+    }
   }
 
   // Currently we only support the sharing of variables between master and

openmp/libomptarget/deviceRTLs/nvptx/src/omptarget-nvptx.h

@@ -263,6 +263,9 @@ class omptarget_nvptx_TeamDescr {
     // If this is invoked by the master thread of the master warp then intialize
     // it with a smaller slot.
     if (IsMasterThread) {
+      // Do not initalize this slot again if it has already been initalized.
+      if (master_rootS[0].DataEnd == &master_rootS[0].Data[0] + DS_Slot_Size)
+        return 0;
       // Initialize the pointer to the end of the slot given the size of the
       // data section. DataEnd is non-inclusive.
       master_rootS[0].DataEnd = &master_rootS[0].Data[0] + DS_Slot_Size;
@@ -272,6 +275,10 @@ class omptarget_nvptx_TeamDescr {
       master_rootS[0].PrevSlotStackPtr = 0;
       return (__kmpc_data_sharing_slot *)&master_rootS[0];
     }
+    // Do not initalize this slot again if it has already been initalized.
+    if (worker_rootS[wid].DataEnd ==
+        &worker_rootS[wid].Data[0] + DS_Worker_Warp_Slot_Size)
+      return 0;
     // Initialize the pointer to the end of the slot given the size of the data
     // section. DataEnd is non-inclusive.
     worker_rootS[wid].DataEnd =