Mismatched types in ADDR_EXPR from c-typeck.c:build_function_call

[Paul Schlie]

> Joseph S. Myers writes:
>> Richard Guenther wrote:
>> The following snippet
>> 
>>       /* Differs from default_conversion by not setting TREE_ADDRESSABLE
>>          (because calling an inline function does not mean the function
>>          needs to be separately compiled).  */
>>       fntype = build_type_variant (TREE_TYPE (function),
>>                                    TREE_READONLY (function),
>>                                    TREE_THIS_VOLATILE (function));
>>       fundecl = function;
>>       function = build1 (ADDR_EXPR, build_pointer_type (fntype),
>> function);
>
> If you want to avoid this then you need to arrange for const and noreturn
> attributes on functions always to be represented by qualifiers on the type
> and not on the decl.  This is part of bug 3481.

I wonder if further a read-only 'literal' type qualifier should be added
as an implicitly declared type qualifier, thereby allowing implicitly
declared literal values/references to be effectively and reliably tracked,
without the complexity of relying on the use of READONLY_TREES, etc.

Thereby all literal values are implied to be qualified as a read-only
'literal' object/reference, which has the semantics, that it may not be
assigned/modified, but unlike 'const' may not be cast away; thereby for
example string (i.e. char array) literal references may be reliably passed
to and returned from functions and properly retain their read-only 'literal'
reference semantics. (i.e. allow _FUNCTION_() to return a reference to a
read-only 'literal char[]', and be able to reliably warn and/or prevent
const pointers to read-only 'literal's to be cast away).