Re: nvptx offloading patches [2/n]

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

On Thu, Feb 19, 2015 at 2:09 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, Feb 17, 2015 at 09:55:32PM +0100, Bernd Schmidt wrote:
>> On 02/17/2015 06:10 PM, Jakub Jelinek wrote:
>> >
>> >What exact testcase are you trying to fix with this patch, and how do you
>> >think offloading of code using va_list can work?
>>
>> The exact testcase is any offloaded program - streaming in lto will crash if
>> there is a mismatch in these preloaded nodes.
>>
>> For OpenACC programs using va_list - I don't expect them to work at all. I
>> don't believe the spec considers such issues, and ptx isn't expected to
>> support variadic functions in the first place ("The current version of PTX
>> does not support variadic functions" is what the spec has to say; the gcc
>> port overachieves a little by implementing them anyway).
>
> How do you support printf etc.?  Those are all varargs functions.
>
> Anyway, could following untested patch be used as a temporary hack?
> It might pessimize for GCC5 slightly the intelmic offloading, but I hope
> the way forward is the stdarg late lowering for GCC 6.
>
> Richard on IRC said it might be better for the lto_stream_offload_p
> path to whitelist nodes it has to preload rather than blacklist the ones
> that it doesn't, otherwise e.g. if you try to offload from say x86_64-mingw
> with 32-bit long, but 64-bit pointers to 64-bit intelmic, preloading
> the long_type_node will certainly break lots of things, while not preloading
> them would only be problematic for builtins, we'll need some pass over the
> builtins in the IL in any case, to find out if they are compatible or not,
> adjust if needed and give up otherwise.  But I'd hope it can be worked on
> incrementally, if this patch (plus the approved nvptx offloading patches,
> plus mode_table streaming) makes the nvptx offloading work.

The patch works for me if it helps anything.

Thanks,
Richard.

> 2015-02-19  Bernd Schmidt  <bernds@codesourcery.com>
>             Jakub Jelinek  <jakub@redhat.com>
>
>         * tree-streamer.c (preload_common_nodes): Don't preload
>         TI_VA_LIST* for offloading.
>         * tree-stdarg.c (pass_stdarg::gate): Disable for ACCEL_COMPILER
>         in_lto_p.
>
> --- gcc/tree-streamer.c.jj      2015-02-18 12:36:20.000000000 +0100
> +++ gcc/tree-streamer.c 2015-02-19 13:57:26.089626006 +0100
> @@ -342,7 +342,14 @@ preload_common_nodes (struct streamer_tr
>         && i != TI_TARGET_OPTION_DEFAULT
>         && i != TI_TARGET_OPTION_CURRENT
>         && i != TI_CURRENT_TARGET_PRAGMA
> -       && i != TI_CURRENT_OPTIMIZE_PRAGMA)
> +       && i != TI_CURRENT_OPTIMIZE_PRAGMA
> +       /* Skip va_list* related nodes if offloading.  For native LTO
> +          we want them to be merged for the stdarg pass, for offloading
> +          they might not be identical between host and offloading target.  */
> +       && (!lto_stream_offload_p
> +           || (i != TI_VA_LIST_TYPE
> +               && i != TI_VA_LIST_GPR_COUNTER_FIELD
> +               && i != TI_VA_LIST_FPR_COUNTER_FIELD)))
>        record_common_node (cache, global_trees[i]);
>  }
>
> --- gcc/tree-stdarg.c.jj        2015-02-18 22:55:52.000000000 +0100
> +++ gcc/tree-stdarg.c   2015-02-19 14:00:11.882905823 +0100
> @@ -705,6 +705,13 @@ public:
>    virtual bool gate (function *fun)
>      {
>        return (flag_stdarg_opt
> +#ifdef ACCEL_COMPILER
> +             /* Disable for GCC5 in the offloading compilers, as
> +                va_list and gpr/fpr counter fields are not merged.
> +                In GCC6 when stdarg is lowered late this shouldn't be
> +                an issue.  */
> +             && !in_lto_p
> +#endif
>               /* This optimization is only for stdarg functions.  */
>               && fun->stdarg != 0);
>      }
>
>         Jakub