Allow merging of units with profile feedback run different amount of times

[H.J. Lu]

On Sat, Dec 4, 2010 at 11:33 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
> Hi,
> this patch adds support for merging compilation units with profile feedbacks where
> each unit was run different times.  This is neccesary for LTO profiledbootstrap
> since we do have single libbackend linked into multiple binaries. As a result
> libbackend summaries are trained more times than each of individual binaries.
> It would make more sense to instrument at link time and have profile feedback for
> each binary separately but this will require more changes and thus can't be done
> in stage3.
>
> This patch simply makes the profiles to be scaled up to the largest number of runs
> in the whole program.  This allows profiledbootstrap to pass on x86-64 for C only
> compiler.   Resulting compiler seems smaller and faster than one built with LTO
> only, so it seems to work as expected.
>
> Merging is done by reading in profile summaries per file basis and storing them in
> lto_file_decl_data.  At the end the maximal number of runs is found and
> profiles are re-scaled to work out global sum_max, in merge_profile_summaries.
> We also need to update callgraph counts that is done in merge_profile_summaries
> and BB/edge counts that is done in lto-streamer based on
> count_materialization_scale stored in cgraph nodes.
>
> I will look into failures appearing in C++ and Ada build (profile mismatches).
>
> Bootstrapped/regtested x86_64-linux, will commit it shortly.
>
>        PR tree-optimization/46760
>        * cgraph.c (cgraph_create_node): Initialize count_materialization_scale.
>        * cgraph.h (struct cgraph_node): Add count_materialization_scale.
>        * lto-cgraph.c (lto_output_edge): Fix assert.
>        (lto_output_node): Output count_materialization_scale.
>        (output_profile_summary): Output only runs and sum_max.
>        (input_node): Input count_materialization_scale.
>        (input_profile_summary): Read data into file specific gcov summary.
>        (merge_profile_summaries): New function.
>        (input_cgraph): Update call of input_profile_summary;
>        call merge_profile_summaries.
>        * lto-streamer-in.c (input_cfg): Add count_materialization_scale arg;
>        rescale counts at read in.
>        (intput_bb): Likewise.
>        (input_function): Update call of input_bb.
>        (lto_read_body): Update call of input_cfg.
>        * lto-streamer.h: Inlclude gcov-io.h
>        (lto_file_decl_data): Add gcov_ctr_summary.

It failed to bootstrap:

http://gcc.gnu.org/ml/gcc-regression/2010-12/msg00056.html


H.J.
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