[OpenACC] Prototype OpenMP extension: no_alloc map type modifier

The `no_alloc` map type modifier is an original OpenMP extension for
the sake of supporting OpenACC's `no_create` clause, which will be
implemented in a following commit.  Currently, all testing of
`no_alloc` is via testing for `no_create`.  That is, `no_alloc` is not
well tested outside of translations from OpenACC to OpenMP, so it is
not yet recommended for general use in OpenMP code.

Author: jdenny-ornl

clang/include/clang/AST/OpenMPClause.h

@@ -5278,7 +5278,8 @@ class OMPMapClause final : public OMPMappableExprListClause<OMPMapClause>,
   /// Map-type-modifiers for the 'map' clause.
   OpenMPMapModifierKind MapTypeModifiers[NumberOfOMPMapClauseModifiers] = {
       OMPC_MAP_MODIFIER_unknown, OMPC_MAP_MODIFIER_unknown,
-      OMPC_MAP_MODIFIER_unknown, OMPC_MAP_MODIFIER_unknown};
+      OMPC_MAP_MODIFIER_unknown, OMPC_MAP_MODIFIER_unknown,
+      OMPC_MAP_MODIFIER_unknown};
 
   /// Location of map-type-modifiers for the 'map' clause.
   SourceLocation MapTypeModifiersLoc[NumberOfOMPMapClauseModifiers];

clang/include/clang/Basic/OpenMPKinds.def

@@ -125,6 +125,10 @@ OPENMP_MAP_MODIFIER_KIND(always)
 OPENMP_MAP_MODIFIER_KIND(close)
 OPENMP_MAP_MODIFIER_KIND(mapper)
 OPENMP_MAP_MODIFIER_KIND(present)
+// This is an OpenMP extension for the sake of OpenACC support.
+// TODO: Currently, it is not well tested outside of translations from OpenACC
+// to OpenMP, so it is not yet recommended for general use in OpenMP code.
+OPENMP_MAP_MODIFIER_KIND(no_alloc)
 
 // Modifiers for 'to' clause.
 OPENMP_TO_MODIFIER_KIND(mapper)

clang/lib/CodeGen/CGOpenMPRuntime.cpp

@@ -7840,6 +7840,12 @@ class MappableExprsHandler {
     OMP_MAP_CLOSE = 0x400,
     /// Produce a runtime error if the data is not already allocated.
     OMP_MAP_PRESENT = 0x800,
+    // Skip allocating the data if it is not already allocated.
+    // This is an OpenMP extension for the sake of OpenACC support.
+    // TODO: Currently, it is not well tested outside of translations from
+    // OpenACC to OpenMP, so it is not yet recommended for general use in
+    // OpenMP code.
+    OMP_MAP_NO_ALLOC = 0x1000,
     /// The 16 MSBs of the flags indicate whether the entry is member of some
     /// struct/class.
     OMP_MAP_MEMBER_OF = 0xffff000000000000,
@@ -8059,6 +8065,9 @@ class MappableExprsHandler {
     if (llvm::find(MapModifiers, OMPC_MAP_MODIFIER_present)
         != MapModifiers.end())
       Bits |= OMP_MAP_PRESENT;
+    if (llvm::find(MapModifiers, OMPC_MAP_MODIFIER_no_alloc)
+        != MapModifiers.end())
+      Bits |= OMP_MAP_NO_ALLOC;
     return Bits;
   }
 

clang/lib/Parse/ParseOpenMP.cpp

@@ -3095,7 +3095,8 @@ bool Parser::parseMapTypeModifiers(OpenMPVarListDataTy &Data) {
     OpenMPMapModifierKind TypeModifier = isMapModifier(*this);
     if (TypeModifier == OMPC_MAP_MODIFIER_always ||
         TypeModifier == OMPC_MAP_MODIFIER_close ||
-        TypeModifier == OMPC_MAP_MODIFIER_present) {
+        TypeModifier == OMPC_MAP_MODIFIER_present ||
+        TypeModifier == OMPC_MAP_MODIFIER_no_alloc) {
       Data.MapTypeModifiers.push_back(TypeModifier);
       Data.MapTypeModifiersLoc.push_back(Tok.getLocation());
       ConsumeToken();

clang/lib/Sema/SemaOpenMP.cpp

@@ -17330,7 +17330,8 @@ OMPClause *Sema::ActOnOpenMPMapClause(
     const OMPVarListLocTy &Locs, ArrayRef<Expr *> UnresolvedMappers) {
   OpenMPMapModifierKind Modifiers[] = {
       OMPC_MAP_MODIFIER_unknown, OMPC_MAP_MODIFIER_unknown,
-      OMPC_MAP_MODIFIER_unknown, OMPC_MAP_MODIFIER_unknown};
+      OMPC_MAP_MODIFIER_unknown, OMPC_MAP_MODIFIER_unknown,
+      OMPC_MAP_MODIFIER_unknown};
   SourceLocation ModifiersLoc[NumberOfOMPMapClauseModifiers];
 
   // Process map-type-modifiers, flag errors for duplicate modifiers.

openmp/libomptarget/include/omptarget.h

@@ -51,6 +51,11 @@ enum tgt_map_type {
   OMP_TGT_MAPTYPE_CLOSE           = 0x400,
   // runtime error if not already allocated
   OMP_TGT_MAPTYPE_PRESENT         = 0x800,
+  // skip allocation if not already allocated
+  // This is an OpenMP extension for the sake of OpenACC support.
+  // TODO: Currently, it is not well tested outside of translations from OpenACC
+  // to OpenMP, so it is not yet recommended for general use in OpenMP code.
+  OMP_TGT_MAPTYPE_NO_ALLOC        = 0x1000,
   // member of struct, member given by [16 MSBs] - 1
   OMP_TGT_MAPTYPE_MEMBER_OF       = 0xffff000000000000
 };

openmp/libomptarget/src/device.cpp

@@ -154,7 +154,7 @@ LookupResult DeviceTy::lookupMapping(void *HstPtrBegin, int64_t Size) {
 // to do an illegal mapping.
 void *DeviceTy::getOrAllocTgtPtr(void *HstPtrBegin, void *HstPtrBase,
     int64_t Size, bool &IsNew, bool &IsHostPtr, bool IsImplicit,
-    bool UpdateRefCount, bool HasCloseModifier, bool HasPresentModifier) {
+    bool UpdateRefCount, bool HasCloseModifier, bool DoNotAllocate) {
   void *rc = NULL;
   IsHostPtr = false;
   IsNew = false;
@@ -196,9 +196,8 @@ void *DeviceTy::getOrAllocTgtPtr(void *HstPtrBegin, void *HstPtrBase,
          DPxPTR((uintptr_t)HstPtrBegin), Size, (UpdateRefCount ? " updated" : ""));
       IsHostPtr = true;
       rc = HstPtrBegin;
-    } else if (HasPresentModifier) {
-      DP("Mapping required but does not exist%s for HstPtrBegin=" DPxMOD
-         ", Size=%ld\n",
+    } else if (DoNotAllocate) {
+      DP("Mapping does not exist%s for HstPtrBegin=" DPxMOD ", Size=%ld\n",
          (IsImplicit ? " (implicit)" : ""), DPxPTR(HstPtrBegin), Size);
     } else {
       // If it is not contained and Size > 0 we should create a new entry for it.
@@ -252,14 +251,15 @@ void *DeviceTy::getOrAllocTgtPtr(void *HstPtrBegin, void *HstPtrBase,
 // Return the target pointer begin (where the data will be moved).
 // Decrement the reference counter if called from target_data_end.
 void *DeviceTy::getTgtPtrBegin(void *HstPtrBegin, int64_t Size, bool &IsLast,
-    bool UpdateRefCount, bool &IsHostPtr) {
+    bool UpdateRefCount, bool &IsHostPtr, bool MustContain) {
   void *rc = NULL;
   IsHostPtr = false;
   IsLast = false;
   DataMapMtx.lock();
   LookupResult lr = lookupMapping(HstPtrBegin, Size);
 
-  if (lr.Flags.IsContained || lr.Flags.ExtendsBefore || lr.Flags.ExtendsAfter) {
+  if (lr.Flags.IsContained ||
+      (!MustContain && (lr.Flags.ExtendsBefore || lr.Flags.ExtendsAfter))) {
     auto &HT = *lr.Entry;
     IsLast = HT.getRefCount() == 1;
 

openmp/libomptarget/src/device.h

@@ -175,10 +175,10 @@ struct DeviceTy {
   LookupResult lookupMapping(void *HstPtrBegin, int64_t Size);
   void *getOrAllocTgtPtr(void *HstPtrBegin, void *HstPtrBase, int64_t Size,
       bool &IsNew, bool &IsHostPtr, bool IsImplicit, bool UpdateRefCount = true,
-      bool HasCloseModifier = false, bool HasPresentModifier = false);
+      bool HasCloseModifier = false, bool DoNotAllocate = false);
   void *getTgtPtrBegin(void *HstPtrBegin, int64_t Size);
   void *getTgtPtrBegin(void *HstPtrBegin, int64_t Size, bool &IsLast,
-      bool UpdateRefCount, bool &IsHostPtr);
+      bool UpdateRefCount, bool &IsHostPtr, bool MustContain = false);
   int deallocTgtPtr(void *TgtPtrBegin, int64_t Size, bool ForceDelete,
                     bool HasCloseModifier = false);
   int associatePtr(void *HstPtrBegin, void *TgtPtrBegin, int64_t Size);

openmp/libomptarget/src/omptarget.cpp

@@ -347,6 +347,7 @@ int target_data_begin(DeviceTy &Device, int32_t arg_num, void **args_base,
     // a close map modifier was associated with a map that contained a to.
     bool HasCloseModifier = arg_types[i] & OMP_TGT_MAPTYPE_CLOSE;
     bool HasPresentModifier = arg_types[i] & OMP_TGT_MAPTYPE_PRESENT;
+    bool HasNoAllocModifier = arg_types[i] & OMP_TGT_MAPTYPE_NO_ALLOC;
     // UpdateRef is based on MEMBER_OF instead of TARGET_PARAM because if we
     // have reached this point via __tgt_target_data_begin and not __tgt_target
     // then no argument is marked as TARGET_PARAM ("omp target data map" is not
@@ -376,13 +377,17 @@ int target_data_begin(DeviceTy &Device, int32_t arg_num, void **args_base,
 
     void *TgtPtrBegin = Device.getOrAllocTgtPtr(HstPtrBegin, HstPtrBase,
         data_size, IsNew, IsHostPtr, IsImplicit, UpdateRef, HasCloseModifier,
-        HasPresentModifier);
+        HasPresentModifier || HasNoAllocModifier);
     // If data_size==0, then the argument could be a zero-length pointer to
     // NULL, so getOrAlloc() returning NULL is not an error.
     if (!TgtPtrBegin && data_size) {
       DP("Call to getOrAllocTgtPtr returned null pointer (%s).\n",
-         HasPresentModifier ? "'present' map type modifier"
-                            : "device failure or illegal mapping");
+         HasPresentModifier
+             ? "'present' map type modifier"
+             : HasNoAllocModifier ? "'no_alloc' map type modifier"
+                                  : "device failure or illegal mapping");
+      if (!HasPresentModifier && HasNoAllocModifier)
+        continue;
       OMPT_DISPATCH_CALLBACK_TARGET_MAP();
       return OFFLOAD_FAIL;
     }
@@ -488,13 +493,19 @@ int target_data_end(DeviceTy &Device, int32_t arg_num, void **args_base,
         (arg_types[i] & OMP_TGT_MAPTYPE_PTR_AND_OBJ);
     bool ForceDelete = arg_types[i] & OMP_TGT_MAPTYPE_DELETE;
     bool HasCloseModifier = arg_types[i] & OMP_TGT_MAPTYPE_CLOSE;
+    bool HasNoAllocModifier = arg_types[i] & OMP_TGT_MAPTYPE_NO_ALLOC;
 
     // If PTR_AND_OBJ, HstPtrBegin is address of pointee
     void *TgtPtrBegin = Device.getTgtPtrBegin(HstPtrBegin, data_size, IsLast,
-        UpdateRef, IsHostPtr);
-    DP("There are %" PRId64 " bytes allocated at target address " DPxMOD
-        " - is%s last\n", data_size, DPxPTR(TgtPtrBegin),
-        (IsLast ? "" : " not"));
+        UpdateRef, IsHostPtr, HasNoAllocModifier);
+    if (!TgtPtrBegin) {
+      DP("Data is not allocated on device\n");
+      assert(!IsLast && "expected no deallocation for unallocated data");
+    } else {
+      DP("There are %" PRId64 " bytes allocated at target address " DPxMOD
+          " - is%s last\n", data_size, DPxPTR(TgtPtrBegin),
+          (IsLast ? "" : " not"));
+    }
 
     bool DelEntry = IsLast || ForceDelete;