Do not stream BINFO_VIRTUALs to ltrans unit

Richard Guenther richard.guenther@gmail.com
Tue Jun 14 10:14:00 GMT 2011


On Mon, Jun 13, 2011 at 2:54 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
> Hi,
> by accident I noticed that BINFO_VIRTUALs streaming is really expensive. It
> about doubles amount of IL and types streamed by Mozilla.
>
> One obvious optimization is to not stream into ltrans unit where it is
> too late to do any useful devirtualization anyway.
> Doing so reduces /tmp usage from 1.7GB to 1.1GB and proportionaly reduces
> streaming out time.
>
> Bootstrapped/regtested x86_64-linux.
> OK?

Ok.

Thanks,
Richard.

> Honza
>        * lto-streamer-out.c (lto_output_ts_binfo_tree_pointers): Do not
>        stream BINFO_VIRTUALS to ltrans units.
> Index: lto-streamer-out.c
> ===================================================================
> --- lto-streamer-out.c  (revision 174985)
> +++ lto-streamer-out.c  (working copy)
> @@ -1117,7 +1117,11 @@
>
>   lto_output_tree_or_ref (ob, BINFO_OFFSET (expr), ref_p);
>   lto_output_tree_or_ref (ob, BINFO_VTABLE (expr), ref_p);
> -  lto_output_tree_or_ref (ob, BINFO_VIRTUALS (expr), ref_p);
> +  /* BINFO_VIRTUALS is used to drive type based devirtualizatoin.  It often links
> +     together large portions of programs making it harder to partition.  Becuase
> +     devirtualization is interesting before inlining, only, there is no real
> +     need to ship it into ltrans partition.  */
> +  lto_output_tree_or_ref (ob, flag_wpa ? NULL : BINFO_VIRTUALS (expr), ref_p);
>   lto_output_tree_or_ref (ob, BINFO_VPTR_FIELD (expr), ref_p);
>
>   output_uleb128 (ob, VEC_length (tree, BINFO_BASE_ACCESSES (expr)));
>



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