Various extensions to the vectorizer

Includes additions to the AstVectorizer:

• Vectorize assignments to vector symbols
• Vectorize loops nested within the vectorization axis if all bounds are independent of the axis
• Vectorize array subscripts if all indices and the array expression are independent of the axis
• Handle empty nodes (e.g. comments)

Additions to the x86 instruction set:

• Intrinsics for basic math functions (log, abs, etc.)
• Type conversions

And to the SelectIntrinsics pass:

• Add option to implemenet type conversions using __builtin_convertvector which is supported by most compilers instead of inserting intrinsics. Useful because not all conversions are supported natively on all CPUs.

src/pystencils/backend/transformations/select_intrinsics.py

@@ -48,7 +48,7 @@ class SelectIntrinsics:
         ctx: The current kernel creation context
         platform: Platform object representing the target hardware, which provides the intrinsics
         use_builtin_convertvector: If `True`, type conversions between SIMD
-            vectors use the compiler builtin `__builtin_convertvector` instead
+            vectors use the compiler builtin `!__builtin_convertvector` instead
             of instrinsics. It is supported by Clang >= 3.7, GCC >= 9.1,
             and ICX. Not supported by ICC or MSVC. Activate if you need type
             conversions not natively supported by your CPU, e.g. conversion from