Re: [PATCH 1/2] select .rodata for const volatile variables.

[Richard Biener <richard.guenther@gmail.com>]

On Mon, Dec 5, 2022 at 7:07 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> On 12/2/22 10:52, Cupertino Miranda via Gcc-patches wrote:
> > Changed target code to select .rodata section for 'const volatile'
> > defined variables.
> > This change is in the context of the bugzilla #170181.
> >
> > gcc/ChangeLog:
> >
> >       v850.c(v850_select_section): Changed function.
> I'm not sure this is safe/correct.  ISTM that you need to look at the
> underlying TREE_TYPE to check for const-volatile rather than
> TREE_SIDE_EFFECTS.

Just to quote tree.h:

/* In any expression, decl, or constant, nonzero means it has side effects or
   reevaluation of the whole expression could produce a different value.
   This is set if any subexpression is a function call, a side effect or a
   reference to a volatile variable.  In a ..._DECL, this is set only if the
   declaration said `volatile'.  This will never be set for a constant.  */
#define TREE_SIDE_EFFECTS(NODE) \
  (NON_TYPE_CHECK (NODE)->base.side_effects_flag)

so if exp is a decl then that's the volatile check.

> Of secondary importance is the ChangeLog.  Just saying "Changed
> function" provides no real information.  Something like this would be
> better:
>
>         * config/v850/v850.c (v850_select_section): Put const volatile
>         objects into read-only sections.
>
>
> Jeff
>
>
>
>
> > ---
> >   gcc/config/v850/v850.cc | 1 -
> >   1 file changed, 1 deletion(-)
> >
> > diff --git a/gcc/config/v850/v850.cc b/gcc/config/v850/v850.cc
> > index c7d432990ab..e66893fede4 100644
> > --- a/gcc/config/v850/v850.cc
> > +++ b/gcc/config/v850/v850.cc
> > @@ -2865,7 +2865,6 @@ v850_select_section (tree exp,
> >       {
> >         int is_const;
> >         if (!TREE_READONLY (exp)
> > -       || TREE_SIDE_EFFECTS (exp)
> >         || !DECL_INITIAL (exp)
> >         || (DECL_INITIAL (exp) != error_mark_node
> >             && !TREE_CONSTANT (DECL_INITIAL (exp))))