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Re: Disable ipa-reference with -fprofile-arcs
> On Mon, 10 Jan 2011, Jan Hubicka wrote:
>
> > Hi,
> > this patch workarounds problems with ipa-reference and profile feedback.
> > Profile feedback adds static var access into every function in program.
> > Especially with LTO this makes ipa-reference tables to explode. It is the case
> > for Mozilla build where LTO -fprofile-generate OOms for me after allocating 9GB
> > of bitmaps.
> >
> > lto-Profilebootstrapped/regtested x86_64-linux, OK?
>
> Can't we just identify those vars and not track them at all? They
I think we want to track orhter kinds of artifical vars - not sure what kinds
we produce however. We surely can do some name matching or pass down a flag.
Overall however, I think it is a lot easier to just disable the pass - we are
speaking of -fprofile-generate mode only and clearly ipa-reference needs to go
and be replaced by ipa-PTA (or more fine grained analysis) in longer run.
> are DECL_ARTIFICIAL after all. OTOH, why does one or two bits
> per function blow up memory usage so much?
Because we build mask of vars known to be not set/used by the function. This
usually contains all the counter arrays except the one used by the function.
So we end up with O(n*m) where n is number of functions and m is number of
arrays. For Mozilla this is quite high. I think there are constant number of
arrays for every file, but Mozilla has many files.
We also might go for disabling with -fprofile-generate -fprofile-arcs -flto
only: I plan to drive users for not using LTO for training run anyway (and
modify profiledbootstrap accordingly)
Honza
>
> Richard.
>
> > Honza
> >
> > PR tree-optimization/47233
> > * opts.c (common_handle_option): Disable ipa-reference with profile feedback.
> > Index: opts.c
> > ===================================================================
> > --- opts.c (revision 168596)
> > +++ opts.c (working copy)
> > @@ -1561,6 +1561,11 @@ common_handle_option (struct gcc_options
> > opts->x_flag_value_profile_transformations = value;
> > if (!opts_set->x_flag_inline_functions)
> > opts->x_flag_inline_functions = value;
> > + /* FIXME: Instrumentation we insert makes ipa-reference bitmaps
> > + quadratic. Disable the pass until better memory representation
> > + is done. */
> > + if (!opts_set->x_flag_ipa_reference)
> > + opts->x_flag_ipa_reference = false;
> > break;
> >
> > case OPT_fshow_column: