Re: [PATCH] Refactor handle_section_attribute to reduce nesting and distinguish error cases

[Josh Triplett <josh at joshtriplett dot org>]

On Sun, Aug 24, 2014 at 05:47:23PM -0400, Trevor Saunders wrote:
> On Sun, Aug 24, 2014 at 01:58:52PM -0700, Andrew Pinski wrote:
> > On Sun, Aug 24, 2014 at 1:42 PM, Josh Triplett <josh@joshtriplett.org> wrote:
> > > handle_section_attribute contains many levels of nested conditionals and
> > > branching code flow paths, with the error cases sometimes in the else
> > > case and sometimes in the if case.  Simplify the code flow into a series
> > > of potential failure cases ending with the successful path, with no
> > > nesting and no else clauses.
> > > ---
> > >
> > > I started to work on an extension to the section attribute, and found
> > > myself cleaning up the logic in handle_section_attribute; I wanted to
> > > send this cleanup patch separately.
> > >
> > > I'm not a GCC committer, so I'm looking both for review and for someone
> > > to commit this patch.
> > >
> > >  gcc/ChangeLog           |  5 +++
> > >  gcc/c-family/c-common.c | 91 +++++++++++++++++++++++++------------------------
> > >  2 files changed, 51 insertions(+), 45 deletions(-)
> > >
> > > diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> > > index 703a489..0286bfb 100644
> > > --- a/gcc/ChangeLog
> > > +++ b/gcc/ChangeLog
> > > @@ -1,3 +1,8 @@
> > > +2014-08-24  Josh Triplett  <josh@joshtriplett.org>
> > > +
> > > +       * c-family/c-common.c (handle_section_attribute): Refactor to reduce
> > > +       nesting and distinguish between error cases.
> > > +
> > >  2014-08-24  Oleg Endo  <olegendo@gcc.gnu.org>
> > >
> > >         PR target/61996
> > > diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
> > > index 58b9763..a63eedf 100644
> > > --- a/gcc/c-family/c-common.c
> > > +++ b/gcc/c-family/c-common.c
> > > @@ -7387,58 +7387,59 @@ handle_section_attribute (tree *node, tree ARG_UNUSED (name), tree args,
> > >  {
> > >    tree decl = *node;
> > >
> > > -  if (targetm_common.have_named_sections)
> > > +  if (!targetm_common.have_named_sections)
> > >      {
> > > -      user_defined_section_attribute = true;
> > > +      error_at (DECL_SOURCE_LOCATION (*node),
> > > +               "section attributes are not supported for this target");
> > > +      goto fail;
> > 
> > Why not move this to a different function and then do:
> > 
> > if (function(...))
> >   set_decl_section_name (decl, TREE_STRING_POINTER (TREE_VALUE (args)));
> > else
> >   *no_add_attrs = true;
> > 
> > return NULL_TREE;
> > 
> > This is a way to get away from using gotos.
> 
> or you could just set no_add_attrs to true at the start of the function
> and only set it to false when you know the attr is valid, which saves
> the weirdness of a second function.

Though that would then duplicate the "return NULL_TREE" in many places,
which seems suboptimal (and not much different than "goto fail").

Andrew, any preference between those two approaches?

- Josh Triplett

> Trev
> 
> > 
> > Thanks,
> > Andrew
> > 
> > 
> > > +    }
> > >
> > > -      if ((TREE_CODE (decl) == FUNCTION_DECL
> > > -          || TREE_CODE (decl) == VAR_DECL)
> > > -         && TREE_CODE (TREE_VALUE (args)) == STRING_CST)
> > > -       {
> > > -         if (TREE_CODE (decl) == VAR_DECL
> > > -             && current_function_decl != NULL_TREE
> > > -             && !TREE_STATIC (decl))
> > > -           {
> > > -             error_at (DECL_SOURCE_LOCATION (decl),
> > > -                       "section attribute cannot be specified for "
> > > -                       "local variables");
> > > -             *no_add_attrs = true;
> > > -           }
> > > +  user_defined_section_attribute = true;
> > >
> > > -         /* The decl may have already been given a section attribute
> > > -            from a previous declaration.  Ensure they match.  */
> > > -         else if (DECL_SECTION_NAME (decl) != NULL
> > > -                  && strcmp (DECL_SECTION_NAME (decl),
> > > -                             TREE_STRING_POINTER (TREE_VALUE (args))) != 0)
> > > -           {
> > > -             error ("section of %q+D conflicts with previous declaration",
> > > -                    *node);
> > > -             *no_add_attrs = true;
> > > -           }
> > > -         else if (TREE_CODE (decl) == VAR_DECL
> > > -                  && !targetm.have_tls && targetm.emutls.tmpl_section
> > > -                  && DECL_THREAD_LOCAL_P (decl))
> > > -           {
> > > -             error ("section of %q+D cannot be overridden", *node);
> > > -             *no_add_attrs = true;
> > > -           }
> > > -         else
> > > -           set_decl_section_name (decl,
> > > -                                  TREE_STRING_POINTER (TREE_VALUE (args)));
> > > -       }
> > > -      else
> > > -       {
> > > -         error ("section attribute not allowed for %q+D", *node);
> > > -         *no_add_attrs = true;
> > > -       }
> > > +  if (TREE_CODE (decl) != FUNCTION_DECL && TREE_CODE (decl) != VAR_DECL)
> > > +    {
> > > +      error ("section attribute not allowed for %q+D", *node);
> > > +      goto fail;
> > >      }
> > > -  else
> > > +
> > > +  if (TREE_CODE (TREE_VALUE (args)) != STRING_CST)
> > >      {
> > > -      error_at (DECL_SOURCE_LOCATION (*node),
> > > -               "section attributes are not supported for this target");
> > > -      *no_add_attrs = true;
> > > +      error ("section attribute argument not a string constant");
> > > +      goto fail;
> > > +    }
> > > +
> > > +  if (TREE_CODE (decl) == VAR_DECL
> > > +      && current_function_decl != NULL_TREE
> > > +      && !TREE_STATIC (decl))
> > > +    {
> > > +      error_at (DECL_SOURCE_LOCATION (decl),
> > > +                "section attribute cannot be specified for local variables");
> > > +      goto fail;
> > >      }
> > >
> > > +  /* The decl may have already been given a section attribute
> > > +     from a previous declaration.  Ensure they match.  */
> > > +  if (DECL_SECTION_NAME (decl) != NULL
> > > +      && strcmp (DECL_SECTION_NAME (decl),
> > > +                 TREE_STRING_POINTER (TREE_VALUE (args))) != 0)
> > > +    {
> > > +      error ("section of %q+D conflicts with previous declaration", *node);
> > > +      goto fail;
> > > +    }
> > > +
> > > +  if (TREE_CODE (decl) == VAR_DECL
> > > +      && !targetm.have_tls && targetm.emutls.tmpl_section
> > > +      && DECL_THREAD_LOCAL_P (decl))
> > > +    {
> > > +      error ("section of %q+D cannot be overridden", *node);
> > > +      goto fail;
> > > +    }
> > > +
> > > +  set_decl_section_name (decl, TREE_STRING_POINTER (TREE_VALUE (args)));
> > > +  return NULL_TREE;
> > > +
> > > +fail:
> > > +  *no_add_attrs = true;
> > >    return NULL_TREE;
> > >  }
> > >
> > > --
> > > 2.1.0
> > >