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/ast_vectorizer.py

@@ -156,6 +156,10 @@ class VectorizationContext:
             )
         return PsVectorType(scalar_type, self._lanes)
 
+    def axis_ctr_dependees(self, symbols: set[PsSymbol]) -> set[PsSymbol]:
+        """Returns all symbols in `symbols` that depend on the axis counter."""
+        return symbols & (self.vectorized_symbols.keys() | {self.axis.counter})
+
 
 @dataclass
 class Affine:
@@ -303,16 +307,13 @@ class AstVectorizer:
                 return PsAssignment(lhs_vec, rhs_vec)
 
             case PsLoop(counter, start, stop, step, body):
+                # Check that loop bounds are lane-invariant
                 free_symbols = (
                     self._collect_symbols(start)
                     | self._collect_symbols(stop)
                     | self._collect_symbols(step)
                 )
-
-                # Check that loop bounds are lane-invariant
-                vec_dependencies = free_symbols & (
-                    vc.vectorized_symbols.keys() | {vc.axis.counter}
-                )
+                vec_dependencies = vc.axis_ctr_dependees(free_symbols)
                 if vec_dependencies:
                     raise VectorizationError(
                         "Unable to vectorize loop depending on vectorized symbols:\n"
@@ -469,14 +470,11 @@ class AstVectorizer:
                     vec_expr = PsVecBroadcast(vc.lanes, expr.clone())
 
             case PsSubscript(array, index):
+                # Check that array expression and indices are lane-invariant
                 free_symbols = self._collect_symbols(array).union(
                     *[self._collect_symbols(i) for i in index]
                 )
-
-                # Check that array expression and indices are lane-invariant
-                vec_dependencies = free_symbols & (
-                    vc.vectorized_symbols.keys() | {vc.axis.counter}
-                )
+                vec_dependencies = vc.axis_ctr_dependees(free_symbols)
                 if vec_dependencies:
                     raise VectorizationError(
                         "Unable to vectorize array subscript depending on vectorized symbols:\n"