RFC re VIEW_CONVERT_EXPR

[Richard Kenner]

    I don't know.  The use of VCE I'd envisioned in the beginning,

	int i; float f;
	f = V_C_E<float>(i);

    doesn't seem to match a 'reference'.  Nor is even the normal
    Ada usage of this referring to some subcomponent of an object.

    What's your argument for why it should be in 'r'?

That it's inside an LHS nest (e.g, you can have a COMPONENT_REF of a
VIEW_CONVERT_EXPR of an ARRAY_REF).  With your change to REALPART_EXPR
and IMAGPART_EXPR and this one, the valid LHS operations are precisely
those in 'r' except INDIRECT_REF (which should be moved to 'e') and
NOP_EXPR and CONVERT_EXPR (which should be disallowed).

Then handled_component_p simply becomes a test of TREE_CODE_CLASS
being 'r'.