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/cpu/cpujit.py

@@ -140,7 +140,17 @@ def get_llc_command():
 
     We try if one of the following is in PATH: llc, llc-10, llc-9, llc-8, llc-7, llc-6
     """
-    candidates = ['llc', 'llc-10', 'llc-9', 'llc-8', 'llc-7', 'llc-6']
+    candidates = ['llc'] + [f'llc-{i}' for i in range(14, 7, -1)]
+    found_executables = (e for e in candidates if shutil.which(e))
+    return next(found_executables, None)
+
+
+def get_clang_command():
+    """Try to get executable for llvm's IR compiler llc
+
+    We try if one of the following is in PATH: llc, llc-10, llc-9, llc-8, llc-7, llc-6
+    """
+    candidates = ['clang'] + [f'clang-{i}' for i in range(14, 7, -1)]
     found_executables = (e for e in candidates if shutil.which(e))
     return next(found_executables, None)