WIP: Opencl to SPIR-V ahead-of-time compilation

This does not yet use the pystencils' cache folder or disk caching of the compilation.

This can be used to embed compiled bytecode into waLBerla executables as I do with my Vulkan wrapper. Not sure if this is a good way to go but at least we can experiment with it.

A good way to proceed with this MR is also a comparison between hip/sicl/ocl/vulkan in order to identify a suitable backend for pystencils.

pystencils/opencl/spirv.py

@@ -66,8 +66,10 @@ def _opencl_to_spriv(opencl_code,
             f.write(code)
         if opencl_output_file:
             shutil.copy(cl_file, opencl_output_file)
+        spirv_opt = shutil.which('spirv-opt')
 
         if spirv_compiler == 'clspv':
+            # You can pass -cl-std=CLC++ to clspv to compile C++ for OpenCL (you wil also need -inline-entry-points)
             assert 0 == call(['clspv',
                               *OCL_FAST_MATH_FLAGS,
                               *(['-cl-single-precision-constant'] if silence_warnings else []),
@@ -83,17 +85,10 @@ def _opencl_to_spriv(opencl_code,
             if code_as_c_array:
                 raise("Output as C-array only supported with clspv")
             clang = get_clang_command()
-            if not clang:
-                raise('Could not find clang!')
             llvm_spirv = shutil.which('llvm-spirv')
-            if not llvm_spirv:
-                raise('Could not find llvm-spirv!')
-            spirv_opt = shutil.which('spirv-opt')
-            if not spirv_opt:
-                raise('Could not find llvm-opt!')
 
             assert 0 == call([clang,
-                              '-cc1',  # or cc1?
+                              '-cc1',
                               '-x', 'cl',
                               '-triple', 'spir',
                               f"-cl-std=CL{opencl_version}",
@@ -105,15 +100,15 @@ def _opencl_to_spriv(opencl_code,
                               '-o',
                               llvm_file])
             assert 0 == call([llvm_spirv,
-                              llvm_file,  # or cc1?
+                              llvm_file,
                               '-o',
                               spirv_file])
-            assert 0 == call([spirv_opt,
-                              spirv_file,  # or cc1?
-                              '-o',
-                              output_file])
-        assert isfile(spirv_file)
-        shutil.copy(spirv_file, output_file)
+
+        assert 0 == call([spirv_opt,
+                          spirv_file,
+                          '-o',
+                          output_file])
+        assert isfile(output_file)
 
 
 def _opencl_ast_to_spriv(ast,