Assert assemble_external is only called during or after expanding to RTL

Hello,

This patch tightens the conditions on when assemble_external() may be
called. It also removes a comment that "most platforms do not define
ASM_OUTPUT_EXTERNAL", because hasn't been true since r119764 added a
definition of ASM_OUTPUT_EXTERNAL to elfos.h.

This is the first step toward addressing PR17982 on the trunk for GCC
4.8. The next step is to change pending_assemble_externals to
pending_assemble_visibility, and fold assemble_external_real() back
into assemble_external.

But first, this patch. I don't think this is very risky, because GCC
now always works in unit-at-a-time mode. But I think it would be good
to have this on the trunk for a week or so before proceeding.

Bootstrapped & tested on x86_64-unknown-linux-gnu. OK for trunk?

Ciao!
Steven



       * varasm.c (assemble_external): Assert this function is only called
       during or after expanding to RTL.

On Sat, Mar 24, 2012 at 9:25 PM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
> Hello,
>
> This patch tightens the conditions on when assemble_external() may be
> called. It also removes a comment that "most platforms do not define
> ASM_OUTPUT_EXTERNAL", because hasn't been true since r119764 added a
> definition of ASM_OUTPUT_EXTERNAL to elfos.h.
>
> This is the first step toward addressing PR17982 on the trunk for GCC
> 4.8. The next step is to change pending_assemble_externals to
> pending_assemble_visibility, and fold assemble_external_real() back
> into assemble_external.
>
> But first, this patch. I don't think this is very risky, because GCC
> now always works in unit-at-a-time mode. But I think it would be good
> to have this on the trunk for a week or so before proceeding.
>
> Bootstrapped & tested on x86_64-unknown-linux-gnu. OK for trunk?

Ok.  Though I wonder why callers cannot simply push these decls to
the pending varpool queue and we might do a final run over it,
assembling things?  [or why we call assemble_external that late at all ...]

Richard.

> Ciao!
> Steven
>
>
>
>        * varasm.c (assemble_external): Assert this function is only called
>        during or after expanding to RTL.
>
> Index: varasm.c
> ===================================================================
> --- varasm.c    (revision 185762)
> +++ varasm.c    (working copy)
> @@ -2166,12 +2166,18 @@ static GTY(()) tree weak_decls;
>  void
>  assemble_external (tree decl ATTRIBUTE_UNUSED)
>  {
> -  /* Because most platforms do not define ASM_OUTPUT_EXTERNAL, the
> -     main body of this code is only rarely exercised.  To provide some
> -     testing, on all platforms, we make sure that the ASM_OUT_FILE is
> -     open.  If it's not, we should not be calling this function.  */
> +  /*  Make sure that the ASM_OUT_FILE is open.
> +      If it's not, we should not be calling this function.  */
>   gcc_assert (asm_out_file);
>
> +  /* This function should only be called if we are expanding, or have
> +     expanded, to RTL.
> +     Ideally, only final.c would be calling this function, but it is
> +     not clear whether that would break things somehow.  See PR 17982
> +     for further discussion.  */
> +  gcc_assert (cgraph_state == CGRAPH_STATE_EXPANSION
> +              || cgraph_state == CGRAPH_STATE_FINISHED);
> +
>   if (!DECL_P (decl) || !DECL_EXTERNAL (decl) || !TREE_PUBLIC (decl))
>     return;

On Mon, Mar 26, 2012 at 9:25 AM, Richard Guenther
<richard.guenther@gmail.com> wrote:
> On Sat, Mar 24, 2012 at 9:25 PM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
>> Hello,
>>
>> This patch tightens the conditions on when assemble_external() may be
>> called. It also removes a comment that "most platforms do not define
>> ASM_OUTPUT_EXTERNAL", because hasn't been true since r119764 added a
>> definition of ASM_OUTPUT_EXTERNAL to elfos.h.
>>
>> This is the first step toward addressing PR17982 on the trunk for GCC
>> 4.8. The next step is to change pending_assemble_externals to
>> pending_assemble_visibility, and fold assemble_external_real() back
>> into assemble_external.
>>
>> But first, this patch. I don't think this is very risky, because GCC
>> now always works in unit-at-a-time mode. But I think it would be good
>> to have this on the trunk for a week or so before proceeding.
>>
>> Bootstrapped & tested on x86_64-unknown-linux-gnu. OK for trunk?
>
> Ok.  Though I wonder why callers cannot simply push these decls to
> the pending varpool queue and we might do a final run over it,
> assembling things?  [or why we call assemble_external that late at all ...]

The idea is to only call assemble_external as late as possible, i.e.
in final. See PR17982. The pending_assemble_external queue was a hack
/ work-around for a problem with c-decl calling DECL_RTL early. Before
that hack was introduced, any call to assemble_external would set
DECL_ASSEMBLER_NAME and DECL_RTL, and write out something to
asm_out_file, during parsing. I'm trying to clean up that
pending_assemble_external mess, because it causes some nasty compile
time problems (PR 52640).

Ciao!
Steven