On Wed, Feb 22, 2023 at 05:22:57PM +0100, Laszlo Ersek wrote:
> On 2/22/23 10:40, Laszlo Ersek wrote:
> > On 2/22/23 09:17, Richard W.M. Jones wrote:
> >> On Tue, Feb 21, 2023 at 05:23:52PM +0100, Laszlo Ersek wrote:
> >
> >>> This is doable, but I hope it's not expected that
> >>> DEFINE_POINTER_VECTOR_TYPE() *enforce* that the element type be a pointer
> >>> :)
> >>
> >>
> >> You might ignore this for a first draft, but it is apparently possible
> >> to statically detect this (at least, if using GCC/clang):
> >>
> >> https://stackoverflow.com/questions/19255148/check-if-a-macro-argument-is-a-pointer-or-not
> >
> > Right, we already use at least __builtin_types_compatible_p in
> > TYPE_IS_ARRAY(); that's what I wouldn't want more of, at least via this
> > series.
>
> OK, summarizing the TODOs for this particular patch:
>
> 1. keep _iter
>
> 2. rename DEFINE_VECTOR_EMPTY to ADD_VECTOR_EMPTY_METHOD
>
> 3. introduce DEFINE_POINTER_VECTOR_TYPE that expands to DEFINE_VECTOR_TYPE +
> ADD_VECTOR_EMPTY_METHOD
>
> 4. DEFINE_POINTER_VECTOR_TYPE (and ADD_VECTOR_EMPTY_METHOD) should not take
> "free" as a parameter; ADD_VECTOR_EMPTY_METHOD should hard-code it
>
> 5. in "common/utils/string-vector.h", don't ADD_VECTOR_EMPTY_METHOD; instead,
> replace DEFINE_VECTOR_TYPE with DEFINE_POINTER_VECTOR_TYPE.
>
> 6. in ADD_VECTOR_EMPTY_METHOD, consider checking that the element type is a
> pointer type.
Sounds like a plan.
> --*--
>
> Re: 6, I find that the stackoverflow solution above is too complicated. I
> mentioned our existent TYPE_IS_ARRAY macro:
>
> #define TYPE_IS_ARRAY(a) \
> (!__builtin_types_compatible_p (typeof (a), typeof (&(a)[0])))
>
> This is perfectly usable for our purposes, as !TYPE_IS_ARRAY(). The reason is
> that when this macro is applied to anything that's *neither* a pointer *nor*
> an array, we get a build error at once:
>
> #define TYPE_IS_ARRAY(a) \
> (!__builtin_types_compatible_p (typeof (a), typeof (&(a)[0])))
>
> int main(void)
> {
> int x[5];
> int *y;
> int z;
>
> TYPE_IS_ARRAY (x);
> TYPE_IS_ARRAY (y);
> TYPE_IS_ARRAY (z);
> return 0;
> }
>
> --->
>
> isptr.c: In function ‘main’:
> isptr.c:2:59: error: subscripted value is neither array nor pointer nor vector
> 2 | (!__builtin_types_compatible_p (typeof (a), typeof (&(a)[0])))
> | ^
> isptr.c:12:3: note: in expansion of macro ‘TYPE_IS_ARRAY’
> 12 | TYPE_IS_ARRAY (z);
> | ^~~~~~~~~~~~~
>
> (the "nor vector" part of the error message can most likely be ignored, I
> believe it refers to the C++ standard library vector class)
>
> Thus, with types that are neither pointers nor arrays nicely caught at
> compilation time, !TYPE_IS_ARRAY stands for "pointer".
Nice .. but probably want to define:
#define TYPE_IS_POINTER(p) (!TYPE_IS_ARRAY(p))
> I'll experiment with this a bit, but if it becomes too complex, I'll likely
> drop step 6.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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