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/codegen/target.py

@@ -115,6 +115,18 @@ class Target(Flag):
             return avail_targets.pop()
         else:
             return Target.GenericCPU
+        
+    @staticmethod
+    def available_targets() -> list[Target]:
+        targets = [Target.GenericCPU]
+        try:
+            import cupy  # noqa: F401
+            targets.append(Target.CUDA)
+        except ImportError:
+            pass
+
+        targets += Target.available_vector_cpu_targets()
+        return targets
 
     @staticmethod
     def available_vector_cpu_targets() -> list[Target]: