Fix CPU-only builds when NRN_ENABLE_GPU=OFF

treeset.cpp: include neuron/gpu/offload.hpp unconditionally so nrn_pragma_acc
macros are no-op stubs without GPU/OpenACC.

nrnivmodl.in: prefix every line of GPU-only nocmodl guards (not just the if).

gpu.py: skip _sync_to_hoc when HOC gpu_* methods are absent (non-GPU builds).

test_fast_imem.py: import backend_helper only when backend tests will run;
ship backend_helper.py with basic_tests SCRIPT_PATTERNS.

Author: nrnhines

bin/nrnivmodl.in

@@ -107,13 +107,13 @@ while [ "$1" ] ; do
 done
 
 @NRN_ENABLE_GPU_TRUE@if [ "$ForceNOCMODL" = true ]; then
-    echo "ERROR: -nocmodl is not supported with NRN_ENABLE_GPU builds. Use NMODL (default) instead."
-    exit 1
-fi
+@NRN_ENABLE_GPU_TRUE@    echo "ERROR: -nocmodl is not supported with NRN_ENABLE_GPU builds. Use NMODL (default) instead."
+@NRN_ENABLE_GPU_TRUE@    exit 1
+@NRN_ENABLE_GPU_TRUE@fi
 @NRN_ENABLE_GPU_TRUE@if [ -n "$UserNMODLBIN" ] && echo "$UserNMODLBIN" | grep -q nocmodl; then
-    echo "ERROR: NOCMODL cannot be used with NRN_ENABLE_GPU builds. Use NMODL (default) instead."
-    exit 1
-fi
+@NRN_ENABLE_GPU_TRUE@    echo "ERROR: NOCMODL cannot be used with NRN_ENABLE_GPU builds. Use NMODL (default) instead."
+@NRN_ENABLE_GPU_TRUE@    exit 1
+@NRN_ENABLE_GPU_TRUE@fi
 
 echo "$PWD"
 

share/lib/python/neuron/gpu.py

@@ -130,6 +130,9 @@ def _sync_to_hoc(self):
             pc = self._pc()
         except Exception:
             return
+        # HOC gpu_* methods are registered only when NRN_ENABLE_GPU is set at build time.
+        if not hasattr(pc, "gpu_enable"):
+            return
         pc.gpu_enable(int(self._enable))
         pc.gpu_backend(self._backend)
         pc.gpu_device_count(int(self._device_count))

src/neuron/gpu/offload.hpp

@@ -24,6 +24,10 @@
 #define nrn_gpu_pragma_omp(x)
 #endif
 
+// nrnoc GPU paths (e.g. treeset.cpp) use the same names as CoreNEURON offload.hpp.
+#define nrn_pragma_acc(x) nrn_gpu_pragma_acc(x)
+#define nrn_pragma_omp(x) nrn_gpu_pragma_omp(x)
+
 #include <cstddef>
 #include <stdexcept>
 #include <string_view>

src/nrnoc/treeset.cpp

@@ -22,8 +22,8 @@
 #include "utils/profile/profiler_interface.h"
 #include "multicore.h"
 
+#include "neuron/gpu/offload.hpp"
 #if defined(NRN_ENABLE_GPU)
-#include "coreneuron/utils/offload.hpp"
 #include "neuron/gpu/sync.hpp"
 #endif
 

test/CMakeLists.txt

@@ -385,7 +385,8 @@ if(NRN_ENABLE_PYTHON)
         PRELOAD_SANITIZER
         ENVIRONMENT "CC=${CMAKE_C_COMPILER}"
         COMMAND "${exe}" ${pytest} "./test/${group}"
-        SCRIPT_PATTERNS "test/${group}/*.json" "test/${group}/*.py")
+        SCRIPT_PATTERNS "test/${group}/*.json" "test/${group}/*.py"
+                        "test/coreneuron/backend_helper.py")
     endforeach()
   endforeach()
 

test/pytest_coreneuron/test_fast_imem.py

@@ -292,14 +292,18 @@ def cmp(name, **kwargs):
         import sys
         from pathlib import Path
 
-        sys.path.insert(0, str(Path(__file__).resolve().parent.parent / "coreneuron"))
-        from backend_helper import (
-            disable_test_backend,
-            enable_test_backend,
-            is_native_backend_test,
-        )
-
-        if is_native_backend_test() or coreneuron_available():
+        run_backend_tests = coreneuron_available()
+        backend_dir = Path(__file__).resolve().parent.parent / "coreneuron"
+        if (backend_dir / "backend_helper.py").is_file():
+            sys.path.insert(0, str(backend_dir))
+            from backend_helper import (
+                disable_test_backend,
+                enable_test_backend,
+                is_native_backend_test,
+            )
+
+            run_backend_tests = run_backend_tests or is_native_backend_test()
+        if run_backend_tests:
             tolerance = 5e-11
             enable_test_backend()
             run(tstop)