Re: [google/4_8] Disable -g/-gmlt during LIPO instrumentation

[Xinliang David Li <davidxl at google dot com>]

The key is that grouping results should not dependent on the presence
of -g flags.  The downside of the patch is that it may slightly
underestimate the memory pressure at profile-use time, but that should
not be a big problem.

David

On Fri, Sep 27, 2013 at 1:18 PM, Rong Xu <xur@google.com> wrote:
> I don't quite understand here. We use the profile-generate memory
> consumption to estimate the profile use memory consumption.
> we still have -g/-gmlt in profile-use compilation. Will this change
> effectively under estimate the memory use in the use phrase?
>
> -Rong
>
> On Fri, Sep 27, 2013 at 11:50 AM, Teresa Johnson <tejohnson@google.com> wrote:
>> David and Rong,
>>
>> The following patch will disable -g/-gmlt when instrumenting for LIPO
>> since they will affect the recorded ggc_memory used in the module
>> grouping decision. Added -fripa-allow-debug to override this behavior.
>>
>> Passes regression tests and simple tests on the new functionality.
>>
>> Ok for google/4_8?
>>
>> Teresa
>>
>> 2013-09-27  Teresa Johnson  <tejohnson@google.com>
>>
>>         * opts.c (finish_options): Suppress -g/-gmlt when we are
>>         building for LIPO instrumention.
>>         * common.opt (fripa-allow-debug): New option.
>>
>> Index: opts.c
>> ===================================================================
>> --- opts.c      (revision 202976)
>> +++ opts.c      (working copy)
>> @@ -799,7 +799,7 @@ finish_options (struct gcc_options *opts, struct g
>>  #endif
>>        if (!opts->x_flag_fat_lto_objects && !HAVE_LTO_PLUGIN)
>>          error_at (loc, "-fno-fat-lto-objects are supported only with
>> linker plugin.");
>> -}
>> +    }
>>    if ((opts->x_flag_lto_partition_balanced != 0) +
>> (opts->x_flag_lto_partition_1to1 != 0)
>>         + (opts->x_flag_lto_partition_none != 0) >= 1)
>>      {
>> @@ -852,6 +852,26 @@ finish_options (struct gcc_options *opts, struct g
>>    /* Turn on -ffunction-sections when -freorder-functions=* is used.  */
>>    if (opts->x_flag_reorder_functions > 1)
>>      opts->x_flag_function_sections = 1;
>> +
>> +  /* LIPO module grouping depends on the memory consumed by the profile-gen
>> +     parsing phase, recorded in a per-module ggc_memory field of the module
>> +     info struct. This will be higher when debug generation is on via
>> +     -g/-gmlt, which causes the FE to generate debug structures that will
>> +     increase the ggc_total_memory. This could in theory cause the module
>> +     groups to be slightly more conservative. Disable -g/-gmlt under
>> +     -fripa -fprofile-generate, but provide an option to override this
>> +     in case we actually need to debug an instrumented binary.  */
>> +  if (opts->x_profile_arc_flag
>> +      && opts->x_flag_dyn_ipa
>> +      && opts->x_debug_info_level != DINFO_LEVEL_NONE
>> +      && !opts->x_flag_dyn_ipa_allow_debug)
>> +    {
>> +      inform (loc,
>> +             "Debug generation via -g option disabled under -fripa "
>> +              "-fprofile-generate (use -fripa-allow-debug to override)");
>> +      set_debug_level (NO_DEBUG, DEFAULT_GDB_EXTENSIONS, "0", opts, opts_set,
>> +                       loc);
>> +    }
>>  }
>>
>>  #define LEFT_COLUMN    27
>> Index: common.opt
>> ===================================================================
>> --- common.opt  (revision 202976)
>> +++ common.opt  (working copy)
>> @@ -1155,6 +1155,10 @@ fripa
>>  Common Report Var(flag_dyn_ipa)
>>  Perform Dynamic Inter-Procedural Analysis.
>>
>> +fripa-allow-debug
>> +Common Report Var(flag_dyn_ipa_allow_debug) Init(0)
>> +Allow -g enablement for -fripa -fprofile-generate compiles.
>> +
>>  fripa-disallow-asm-modules
>>  Common Report Var(flag_ripa_disallow_asm_modules)
>>  Don't import an auxiliary module if it contains asm statements
>>
>> --
>> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413