Re: [Patch]: Uncouple size_t and sizetype

[Richard Guenther <richard dot guenther at gmail dot com>]

On Fri, Mar 16, 2012 at 11:39 AM, Tristan Gingold <gingold@adacore.com> wrote:
> Hi,
>
> currently sizetype precision (cf store-layout.c:initialize_sizetypes) is the same as size_t.
> This is an issue on VMS, where size_t is 'unsigned int', but we'd like to have a 64 bit sizetype
> for Ada. ?My understanding is that ISO-C doesn't require size_t precision to match the one of
> void *.
>
> We can't really lie about size_t because it is exposed in API (such as writev).
>
> I don't see any reason (other than historic one) to have an exact match between sizetype and size_t.
> So this patch adds an hook to allow targets to define sizetype.

Well, there is at least "common sense" that couples size_t and sizetype.
As you can at most allocate size_t memory via malloc (due to its size_t
use for the size) sizes larger than what fits into size_t do not make much
sense.  Thus, a sizetype larger than size_t does not make much sense.

The middle-end of course would not care much what you use for sizetype.
But be warned - if the mode for sizetype is different of ptr_mode things
are going to be interesting for you (yes, ptr_mode, not Pmode).

> I initially thought about using Pmode precision for sizetype precision, but there are a few machines
> (m32c, sh, h8300) where the precisions aren't the same. ?I don't know wether this is on purpose or
> unintentional.

At least for m32c it is IIRC because 24bit computations are soo expensive
on that target, so HImode is chosen for sizetype.

So - why do you need a 64bit sizetype again? ;)

Can it be that you don't really need 64bit sizes but you hit issues with
sizetype != ptr_mode size?

Btw, while we are transitioning to target hooks in this case I'd prefer
a target macro alongside the existing SIZE_TYPE, etc. ones.

Richard.

> Manually tested on ia64 and alpha vms.
> Not yet regression tested on a more common machine.
>
> Comments are welcome,
> Tristan.
>
> 2012-03-16 ?Tristan Gingold ?<gingold@adacore.com>
>
> ? ? ? ?* target.def (sizetype_cdecl): New hook.
> ? ? ? ?* stor-layout.c (initialize_sizetypes): Use sizetype_cdecl hook
> ? ? ? ?to get sizetype name.
> ? ? ? ?* targhooks.c (default_sizetype_cdecl): New function.
> ? ? ? ?* targhooks.h (default_sizetype_cdecl): New prototype.
> ? ? ? ?* doc/tm.texi.in (Type Layout): Add TARGET_SIZETYPE_CDECL hook.
> ? ? ? ?* doc/tm.texi: Regenerate.
> ? ? ? ?* config/vms/vms.h (SIZE_TYPE): Always unsigned int.
>
> diff --git a/gcc/config/vms/vms.h b/gcc/config/vms/vms.h
> index e11b1bf..dc44441 100644
> --- a/gcc/config/vms/vms.h
> +++ b/gcc/config/vms/vms.h
> @@ -58,14 +58,12 @@ extern void vms_c_register_includes (const char *, const char *, int);
> ?#define POINTER_SIZE (flag_vms_pointer_size == VMS_POINTER_SIZE_NONE ? 32 : 64)
> ?#define POINTERS_EXTEND_UNSIGNED 0
>
> -/* FIXME: It should always be a 32 bit type. ?*/
> +/* Always 32 bits. ?*/
> ?#undef SIZE_TYPE
> -#define SIZE_TYPE (flag_vms_pointer_size == VMS_POINTER_SIZE_NONE ? \
> - ? ? ? ? ? ? ? ? ?"unsigned int" : "long long unsigned int")
> -/* ???: Defined as a 'int' by dec-c, but obstack.h doesn't like it. ?*/
> +#define SIZE_TYPE ?"unsigned int"
> ?#undef PTRDIFF_TYPE
> ?#define PTRDIFF_TYPE (flag_vms_pointer_size == VMS_POINTER_SIZE_NONE ? \
> ? ? ? ? ? ? ? ? ? ? ? "int" : "long long int")
>
> ?#define C_COMMON_OVERRIDE_OPTIONS vms_c_common_override_options ()
>
> diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
> index 69f8aba..48d7b60 100644
> --- a/gcc/doc/tm.texi
> +++ b/gcc/doc/tm.texi
> @@ -1651,6 +1651,12 @@ for the result of subtracting two pointers. ?The typedef name
> ?If you don't define this macro, the default is @code{"long int"}.
> ?@end defmac
>
> +@deftypefn {Target Hook} {const char *} TARGET_SIZETYPE_CDECL (void)
> +This hooks should return the corresponding C declaration for the internal@code{sizetype} type, from which are also derived @code{bitsizetype} and thesigned variant.
> +
> +If you don't define it, the default is @code{SIZE_TYPE}.
> +@end deftypefn
> +
> ?@defmac WCHAR_TYPE
> ?A C expression for a string describing the name of the data type to use
> ?for wide characters. ?The typedef name @code{wchar_t} is defined using
> diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
> index c24cf1e..0028b76 100644
> --- a/gcc/doc/tm.texi.in
> +++ b/gcc/doc/tm.texi.in
> @@ -1639,6 +1639,8 @@ for the result of subtracting two pointers. ?The typedef name
> ?If you don't define this macro, the default is @code{"long int"}.
> ?@end defmac
>
> +@hook TARGET_SIZETYPE_CDECL
> +
> ?@defmac WCHAR_TYPE
> ?A C expression for a string describing the name of the data type to use
> ?for wide characters. ?The typedef name @code{wchar_t} is defined using
> diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
> index 264edd7..d77abc2 100644
> diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
> index 7c7fabc..5ed0f12 100644
> --- a/gcc/stor-layout.c
> +++ b/gcc/stor-layout.c
> @@ -2383,15 +2383,16 @@ void
> ?initialize_sizetypes (void)
> ?{
> ? int precision, bprecision;
> + ?const char *sizetype_name = targetm.sizetype_cdecl ();
>
> ? /* Get sizetypes precision from the SIZE_TYPE target macro. ?*/
> - ?if (strcmp (SIZE_TYPE, "unsigned int") == 0)
> + ?if (strcmp (sizetype_name, "unsigned int") == 0)
> ? ? precision = INT_TYPE_SIZE;
> - ?else if (strcmp (SIZE_TYPE, "long unsigned int") == 0)
> + ?else if (strcmp (sizetype_name, "long unsigned int") == 0)
> ? ? precision = LONG_TYPE_SIZE;
> - ?else if (strcmp (SIZE_TYPE, "long long unsigned int") == 0)
> + ?else if (strcmp (sizetype_name, "long long unsigned int") == 0)
> ? ? precision = LONG_LONG_TYPE_SIZE;
> - ?else if (strcmp (SIZE_TYPE, "short unsigned int") == 0)
> + ?else if (strcmp (sizetype_name, "short unsigned int") == 0)
> ? ? precision = SHORT_TYPE_SIZE;
> ? else
> ? ? gcc_unreachable ();
> diff --git a/gcc/target.def b/gcc/target.def
> index d658b11..bde3388 100644
> --- a/gcc/target.def
> +++ b/gcc/target.def
> @@ -2674,6 +2674,19 @@ DEFHOOKPOD
> ?@code{bool} @code{true}.",
> ?unsigned char, 1)
>
> +/* The corresponding C declaration for the internal 'sizetype' type, from which
> + ? are also derived 'bitsizetype' and the signed variant. ?The default is
> + ? SIZE_TYPE. ?*/
> +DEFHOOK
> +(sizetype_cdecl,
> + "This hooks should return the corresponding C declaration for the internal\
> +@code{sizetype} type, from which are also derived @code{bitsizetype} and the\
> +signed variant.\n\
> +\n\
> +If you don't define it, the default is @code{SIZE_TYPE}.",
> + const char *, (void),
> + default_sizetype_cdecl)
> +
> ?/* Leave the boolean fields at the end. ?*/
>
> ?/* True if we can create zeroed data by switching to a BSS section
> diff --git a/gcc/targhooks.c b/gcc/targhooks.c
> index 8e3d74e..d490384 100644
> --- a/gcc/targhooks.c
> +++ b/gcc/targhooks.c
> @@ -1340,6 +1340,15 @@ default_get_reg_raw_mode(int regno)
> ? return reg_raw_mode[regno];
> ?}
>
> +/* To be used by almost any targets, except when size_t precision is less than
> + ? pointers precision. ?*/
> +
> +const char *
> +default_sizetype_cdecl (void)
> +{
> + ?return SIZE_TYPE;
> +}
> +
> ?/* Return true if the state of option OPTION should be stored in PCH files
> ? ?and checked by default_pch_valid_p. ?Store the option's current state
> ? ?in STATE if so. ?*/
> diff --git a/gcc/targhooks.h b/gcc/targhooks.h
> index 8618115..41f44f8 100644
> --- a/gcc/targhooks.h
> +++ b/gcc/targhooks.h
> @@ -47,6 +47,7 @@ extern unsigned HOST_WIDE_INT default_shift_truncation_mask
> ? (enum machine_mode);
> ?extern unsigned int default_min_divisions_for_recip_mul (enum machine_mode);
> ?extern int default_mode_rep_extended (enum machine_mode, enum machine_mode);
> +extern const char *default_sizetype_cdecl (void);
>
> ?extern tree default_stack_protect_guard (void);
> ?extern tree default_external_stack_protect_fail (void);
>