1687 fix: Make OpenMP no_create a documented no-op instead of aborting fypp.

docs/documentation/gpuParallelization.md

@@ -73,7 +73,7 @@ This wraps the lines in `code` with parallelization calls to openACC or openMP,
 | `copyinReadOnly` | string list         | None              | Allocates and copies readonly data to GPU and then deallocated on exit                    |
 | `copyout`        | string list         | None              | Allocates data on GPU on entrance and then deallocates and copies to CPU on exit          |
 | `create`         | string list         | None              | Allocates data on GPU on entrance and then deallocates on exit                            |
-| `no_create`      | string list         | None              | Use data in CPU memory unless data is already in GPU memory                               |
+| `no_create`      | string list         | None              | Use data in CPU memory unless data is already in GPU memory (OpenACC only)                |
 | `present`        | string list         | None              | Data that must be present in GPU memory. Increment counter on entrance, decrement on exit |
 | `deviceptr`      | string list         | None              | Pointer variables that are already allocated on GPU memory                                |
 | `attach`         | string list         | None              | Attaches device pointer to device targets on entrance, then detach on exit                |
@@ -184,7 +184,7 @@ Uses FYPP call directive using `#:call`
 | `copyinReadOnly` | string list         | None          | Allocates and copies readonly data to GPU and then deallocated on exit                    |
 | `copyout`        | string list         | None          | Allocates data on GPU on entrance and then deallocates and copies to CPU on exit          |
 | `create`         | string list         | None          | Allocates data on GPU on entrance and then deallocates on exit                            |
-| `no_create`      | string list         | None          | Use data in CPU memory unless data is already in GPU memory                               |
+| `no_create`      | string list         | None          | Use data in CPU memory unless data is already in GPU memory (OpenACC only)                |
 | `present`        | string list         | None          | Data that must be present in GPU memory. Increment counter on entrance, decrement on exit |
 | `deviceptr`      | string list         | None          | Pointer variables that are already allocated on GPU memory                                |
 | `attach`         | string list         | None          | Attaches device pointer to device targets on entrance, then detach on exit                |
@@ -247,7 +247,7 @@ Uses FYPP call directive using `#:call`
 | `copyinReadOnly` | string list | None          | Allocates and copies a readonly variable to GPU and then deallocated on exit                 |
 | `copyout`        | string list | None          | Allocates data on GPU on entrance and then deallocates and copies to CPU on exit             |
 | `create`         | string list | None          | Allocates data on GPU on entrance and then deallocates on exit                               |
-| `no_create`      | string list | None          | Use data in CPU memory unless data is already in GPU memory                                  |
+| `no_create`      | string list | None          | Use data in CPU memory unless data is already in GPU memory (OpenACC only)                   |
 | `present`        | string list | None          | Data that must be present in GPU memory. Increment counter on entrance, decrement on exit    |
 | `deviceptr`      | string list | None          | Pointer variables that are already allocated on GPU memory                                   |
 | `attach`         | string list | None          | Attaches device pointer to device targets on entrance, then detach on exit                   |

src/common/include/omp_macros.fpp

@@ -67,9 +67,14 @@
 #:enddef
 
 #:def OMP_NOCREATE_STR(no_create)
-    #:if no_create is not None
-        #:stop 'no_create is not supported yet'
-    #:endif
+    #! OpenMP has no no_create equivalent, so this is a documented no-op: the variable is
+    #! left to whatever mapping the enclosing region already applies to it. Note that is
+    #! NOT equivalent to no_create on most targets -- OMP_DEFAULT_STR emits nothing unless
+    #! the caller passes default='present', and even then only CCE maps allocatables and
+    #! pointers as present; NVHPC/PGI and the fallback map them tofrom, which copies rather
+    #! than reuses, and LLVMFlang emits nothing at all.
+    #! Do NOT #:stop here: GPU_DATA expands both backends before #if selects one, so
+    #! aborting would break OpenACC builds, where no_create is supported natively.
     #:set no_create_val = ''
     $:no_create_val
 #:enddef
@@ -275,11 +280,32 @@
         & no_create_val.strip('\n') + present_val.strip('\n') + &
         & deviceptr_val.strip('\n') + attach_val.strip('\n') + &
         & default_val.strip('\n')
+    #! An OpenMP `target data` region must carry at least one map, use_device_ptr or
+    #! use_device_addr clause. no_create contributes none (it is a no-op here), and
+    #! `default` is None by default, so GPU_DATA(no_create=x) with no other clause left
+    #! clause_val empty and emitted a bare `!$omp target data` that no compiler accepts.
+    #! Emit the body alone in that case -- a data region with nothing to map has nothing
+    #! to do, which is what GPU_DATA's own #else branch already does when neither backend
+    #! is enabled. A #:stop is not an option here, for the reason in OMP_NOCREATE_STR.
+    #! Only no_create earns that silence. If the caller asked for some other clause and
+    #! the backend produced nothing for it -- default='present' on LLVMFlang, where
+    #! OMP_DEFAULT_STR returns an empty string -- keep emitting the bare directive so the
+    #! build fails loudly rather than silently discarding a region that was asked for.
+    #:set other_clause_requested = copy is not None or copyin is not None or &
+        & copyinReadOnly is not None or copyout is not None or create is not None or &
+        & present is not None or deviceptr is not None or attach is not None or &
+        & default is not None
+    #:set emitted_clause = clause_val.strip() != '' or extraOmpArgs_val.strip() != ''
+    #:set has_clauses = emitted_clause or other_clause_requested
     #:set omp_directive = '!$omp target data ' + clause_val + extraOmpArgs_val.strip('\n')
     #:set end_omp_directive = '!$omp end target data'
-    $:omp_directive
+    #:if has_clauses
+        $:omp_directive
+    #:endif
     $:code
-    $:end_omp_directive
+    #:if has_clauses
+        $:end_omp_directive
+    #:endif
 #:enddef
 
 #:def OMP_ENTER_DATA(copyin=None, copyinReadOnly=None, create=None, attach=None, extraOmpArgs=None)