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Re: [PATCH] Fix profile corruption with -O1 (PR gcov-profile/79259)
- From: Martin Liška <mliska at suse dot cz>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Jan Hubicka <hubicka at ucw dot cz>
- Date: Mon, 30 Jan 2017 16:34:34 +0100
- Subject: Re: [PATCH] Fix profile corruption with -O1 (PR gcov-profile/79259)
- Authentication-results: sourceware.org; auth=none
- References: <2f27dc60-cd74-9edf-5113-ea432348df72@suse.cz> <CAFiYyc3=NYjW0Waqi++VcpCBZHaT7EDXwGbfz88JkD9rzMqOeQ@mail.gmail.com>
On 01/30/2017 04:12 PM, Richard Biener wrote:
> On Mon, Jan 30, 2017 at 4:09 PM, Martin Liška <mliska@suse.cz> wrote:
>> Hello.
>>
>> During investigation of another issue, I accidentally came a profile inconsistency
>> mentioned in the PR. Problem is that flag_ipa_bit_cp is enabled in use stage of PGO
>> and not in instrumentation stage. That causes ccp1 to find nonzero bits and that leads
>> to a CFG changes as a condition can be folded away.
>>
>> Solution is to enable the same flag in generate phase. However I've got one more question:
>> In -fprofile-generate we have 2 more functions available in symtab:
>>
>> _GLOBAL__sub_I_00100_0_c ()
>> {
>> <bb 2> [0.00%]:
>> __gcov_init (&*.LPBX0);
>> return;
>>
>> }
>>
>> _GLOBAL__sub_D_00100_1_c ()
>> {
>> <bb 2> [0.00%]:
>> __gcov_exit ();
>> return;
>>
>> }
>>
>> I'm wondering whether it can potentially influence early inlining decision?
>
> I guess yes...
Looks it should be fine as einline runs before IPA passes, where we create calls
to __gcov_init and __gcov_exit. Thus the original functions do no see the global {cd}tor.
#0 build_init_ctor (gcov_info_type=0x7ffff6a1a000) at ../../gcc/coverage.c:1045
#1 0x0000000000a1086d in coverage_obj_init () at ../../gcc/coverage.c:1144
#2 0x0000000000a10df7 in coverage_finish () at ../../gcc/coverage.c:1272
#3 0x00000000009ff53a in ipa_passes () at ../../gcc/cgraphunit.c:2338
#4 symbol_table::compile (this=this@entry=0x7ffff688a100) at ../../gcc/cgraphunit.c:2460
#5 0x0000000000a018b5 in symbol_table::compile (this=0x7ffff688a100) at ../../gcc/cgraphunit.c:2593
#6 symbol_table::finalize_compilation_unit (this=0x7ffff688a100) at ../../gcc/cgraphunit.c:2619
#7 0x0000000000dfc5fa in compile_file () at ../../gcc/toplev.c:488
#8 0x0000000000685d37 in do_compile () at ../../gcc/toplev.c:1983
#9 toplev::main (this=this@entry=0x7fffffffd8e0, argc=<optimized out>, argc@entry=21, argv=<optimized out>, argv@entry=0x7fffffffd9e8) at ../../gcc/toplev.c:2117
#10 0x0000000000688067 in main (argc=21, argv=0x7fffffffd9e8) at ../../gcc/main.c:39
Martin
>
>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>>
>> Ready to be installed?
>
> Ok.
>
> Thanks,
> Richard.
>
>> Martin