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/platforms/x86.py

@@ -162,7 +162,7 @@ class X86VectorCpu(GenericVectorCpu):
             case PsUnOp() | PsBinOp():
                 func = _x86_op_intrin(self._vector_arch, expr, expr.get_dtype())
                 intrinsic = func(*operands)
-                intrinsic.dtype = expr.dtype
+                intrinsic.dtype = func.return_type
                 return intrinsic
             case _:
                 raise MaterializationError(f"Cannot map {type(expr)} to x86 intrinsic")