Re: Two observations using GDB 13 snapshot

[Simon Marchi <simark@simark.ca>]

On 1/3/23 15:34, Christian Biesinger via Gdb-patches wrote:
> On Tue, Jan 3, 2023 at 3:17 PM Eli Zaretskii <eliz@gnu.org> wrote:
>>
>>> From: Christian Biesinger <cbiesinger@google.com>
>>> Date: Tue, 3 Jan 2023 14:44:56 -0500
>>> Cc: Simon Marchi <simark@simark.ca>, tom@tromey.com, gdb-patches@sourceware.org,
>>>       luis.machado@arm.com
>>>
>>>>> https://stackoverflow.com/questions/36686381/windows-c-runtime-toupper-slow-when-locale-set
>>>>> https://bugs.php.net/bug.php?id=45265
>>>>
>>>> I couldn't see any numbers there about the performance of tolower
>>>> itself, i.e. how many ms per call does it take on Windows vs glibc.
>>>> But if someone can show a patch to try to eliminate the calls to
>>>> tolower, I can try and see if it affects the processing time in this
>>>> scenario.
>>>
>>> Seems like that could be tested by running gdb with LANG=C and/or
>>> commenting out the setlocale calls in gdb/main.c?
>>
>> Setting LANG in the environment doesn't have any effect on Windows,
>> since the Windows version of setlocale is insensitive to LANG and LC_*
>> environment variables.
> 
> Well you could still try commenting out the setlocale call.
> 
> In terms of the code, may be worth trying TOLOWER from
> include/safe-ctype.h instead of tolower()

The tolower call is inside strcasecmp, we don't call tolower directly:

#0  0x77c348d5 in msvcrt!__crtLCMapStringA ()
   from C:\WINDOWS\system32\msvcrt.dll
#1  0x77c348cd in msvcrt!__crtLCMapStringA ()
   from C:\WINDOWS\system32\msvcrt.dll
#2  0x77c30045 in wmktemp () from C:\WINDOWS\system32\msvcrt.dll
#3  0x77c1c992 in tolower () from C:\WINDOWS\system32\msvcrt.dll
#4  0x77c462a1 in stricmp () from C:\WINDOWS\system32\msvcrt.dll
#5  0x005107d3 in strcasecmp (__s2=<optimized out>, __s1=<optimized out>)
    at d:/usr/include/strings.h:92
#6  cooked_index_entry::operator< (this=<optimized out>, other=...)
    at ./dwarf2/cooked-index.h:150

It would be interesting to change that strcasecmp call to strcmp, just
to see if it makes an impact on the performance.  Whether or not that
would be correct is another thing, but it would help see if that
strcasecmp / tolower call is really at fault here.

Simon