Re: [PATCH v2 7/7] grep: add support for PCRE v2

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Wed, May 24, 2017 at 8:23 AM, Junio C Hamano <gitster@pobox.com> wrote:
> Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:
>
>> Add support for v2 of the PCRE API. This is a new major version of
>> PCRE that came out in early 2015[1].
>>
>> The regular expression syntax is the same, but while the API is
>> similar, pretty much every function is either renamed or takes
>> different arguments. Thus using it via entirely new functions makes
>> sense, as opposed to trying to e.g. have one compile_pcre_pattern()
>> that would call either PCRE v1 or v2 functions.
>>
>> Git can now be compiled with either USE_LIBPCRE1=YesPlease or
>> USE_LIBPCRE2=YesPlease, with USE_LIBPCRE=YesPlease currently being a
>> synonym for the former. Providing both is a compile-time error.
>>
>> With earlier patches to enable JIT for PCRE v1 the performance of the
>> release versions of both libraries is almost exactly the same, with
>> PCRE v2 being around 1% slower.
>>
>> However after I reported this to the pcre-dev mailing list[2] I got a
>> lot of help with the API use from Zoltán Herczeg, he subsequently
>> optimized some of the JIT functionality in v2 of the library.
>>
>> Running the p7820-grep-engines.sh performance test against the latest
>> Subversion trunk of both, with both them and git compiled as -O3, and
>> the test run against linux.git, gives the following results. Just the
>> /perl/ tests shown:
>>
>>     $ GIT_PERF_REPEAT_COUNT=30 GIT_PERF_LARGE_REPO=~/g/linux GIT_PERF_MAKE_COMMAND='grep -q LIBPCRE2 Makefile && make -j8 USE_LIBPCRE2=YesPlease CC=~/perl5/installed/bin/gcc NO_R_TO_GCC_LINKER=YesPlease CFLAGS=-O3 LIBPCREDIR=/home/avar/g/pcre2/inst LDFLAGS=-Wl,-rpath,/home/avar/g/pcre2/inst/lib || make -j8 USE_LIBPCRE=YesPlease CC=~/perl5/installed/bin/gcc NO_R_TO_GCC_LINKER=YesPlease CFLAGS=-O3 LIBPCREDIR=/home/avar/g/pcre/inst LDFLAGS=-Wl,-rpath,/home/avar/g/pcre/inst/lib' ./run HEAD~2 HEAD~ HEAD p7820-grep-engines.sh
>>     [...]
>>     Test                                           HEAD~2            HEAD~                    HEAD
>>     ----------------------------------------------------------------------------------------------------------------
>>     7820.3: perl grep 'how.to'                      0.22(0.40+0.48)   0.22(0.31+0.58) +0.0%   0.22(0.26+0.59) +0.0%
>>     7820.7: perl grep '^how to'                     0.27(0.62+0.50)   0.28(0.60+0.50) +3.7%   0.22(0.25+0.60) -18.5%
>>     7820.11: perl grep '[how] to'                   0.33(0.92+0.47)   0.33(0.94+0.45) +0.0%   0.25(0.42+0.51) -24.2%
>>     7820.15: perl grep '(e.t[^ ]*|v.ry) rare'       0.35(1.08+0.46)   0.35(1.12+0.41) +0.0%   0.25(0.52+0.50) -28.6%
>>     7820.19: perl grep 'm(ú|u)lt.b(æ|y)te'          0.30(0.78+0.51)   0.30(0.86+0.42) +0.0%   0.25(0.29+0.54) -16.7%
>>
>> See commit ("perf: add a comparison test of grep regex engines",
>> 2017-04-19) for details on the machine the above test run was executed
>> on.
>>
>> Here HEAD~2 is git with PCRE v1 without JIT, HEAD~ is PCRE v1 with
>> JIT, and HEAD is PCRE v2 (also with JIT). See previous commits of mine
>> mentioning p7820-grep-engines.sh for more details on the test setup.
>>
>> For ease of readability, a different run just of HEAD~ (PCRE v1 with
>> JIT v.s. PCRE v2), again with just the /perl/ tests shown:
>>
>>     Test                                           HEAD~             HEAD
>>     ---------------------------------------------------------------------------------------
>>     7820.3: perl grep 'how.to'                      0.23(0.41+0.47)   0.23(0.26+0.59) +0.0%
>>     7820.7: perl grep '^how to'                     0.27(0.64+0.47)   0.23(0.28+0.56) -14.8%
>>     7820.11: perl grep '[how] to'                   0.34(0.95+0.44)   0.25(0.38+0.56) -26.5%
>>     7820.15: perl grep '(e.t[^ ]*|v.ry) rare'       0.34(1.07+0.46)   0.24(0.52+0.49) -29.4%
>>     7820.19: perl grep 'm(ú|u)lt.b(æ|y)te'          0.30(0.81+0.46)   0.22(0.33+0.54) -26.7%
>>
>> I.e. the two are either neck-to-neck, but PCRE v2 usually pulls ahead,
>> when it does it's around 20% faster.
>>
>> A brief note on thread safety: As noted in pcre2api(3) & pcre2jit(3)
>> the compiled pattern can be shared between threads, but not some of
>> the JIT context, however the grep threading support does all pattern &
>> JIT compilation in separate threads, so this code doesn't need to
>> concern itself with thread safety.
>
> Nicely explained.
>
>> -# Define LIBPCREDIR=/foo/bar if your libpcre header and library files are in
>> +# Currently USE_LIBPCRE is a synonym for USE_LIBPCRE1, define
>> +# USE_LIBPCRE2 instead if you'd like to use version 2 of the PCRE
>> +# library. The USE_LIBPCRE flag will likely be changed to mean v2 by
>> +# default in future releases.
>> +#
>> +# Define LIBPCREDIR=/foo/bar if your PCRE header and library files are in
>>  # /foo/bar/include and /foo/bar/lib directories.
>
> As there is no way to use both, having a single LIBPCREDIR is not a
> hurting limitation, which makes sense.

Will nevertheless add a comment to clarify this.

>> @@ -2241,6 +2258,7 @@ GIT-BUILD-OPTIONS: FORCE
>>       @echo NO_CURL=\''$(subst ','\'',$(subst ','\'',$(NO_CURL)))'\' >>$@+
>>       @echo NO_EXPAT=\''$(subst ','\'',$(subst ','\'',$(NO_EXPAT)))'\' >>$@+
>>       @echo USE_LIBPCRE1=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE)))'\' >>$@+
>
> Shouldn't the line above record $(USE_LIBPCRE1) instead of the
> generic fallback?

Yes, will fix.

>> +     @echo USE_LIBPCRE2=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE2)))'\' >>$@+
>>       @echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@+
>>       @echo NO_PTHREADS=\''$(subst ','\'',$(subst ','\'',$(NO_PTHREADS)))'\' >>$@+
>>       @echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@+
>
>> diff --git a/grep.c b/grep.c
>> index 3c0c30f033..569cf9e290 100644
>> --- a/grep.c
>> +++ b/grep.c
>> @@ -179,22 +179,36 @@ static void grep_set_pattern_type_option(enum grep_pattern_type pattern_type, st
>>       case GREP_PATTERN_TYPE_BRE:
>>               opt->fixed = 0;
>>               opt->pcre1 = 0;
>> +             opt->pcre2 = 0;
>>               break;
>>
>>       case GREP_PATTERN_TYPE_ERE:
>>               opt->fixed = 0;
>>               opt->pcre1 = 0;
>> +             opt->pcre2 = 0;
>>               opt->regflags |= REG_EXTENDED;
>>               break;
>>
>>       case GREP_PATTERN_TYPE_FIXED:
>>               opt->fixed = 1;
>>               opt->pcre1 = 0;
>> +             opt->pcre2 = 0;
>>               break;
>>
>>       case GREP_PATTERN_TYPE_PCRE:
>>               opt->fixed = 0;
>> +#ifdef USE_LIBPCRE2
>> +             opt->pcre1 = 0;
>> +             opt->pcre2 = 1;
>> +#else
>> +             /* It's important that pcre1 always be assigned to
>> +              * even when there's no USE_LIBPCRE* defined. We still
>> +              * call the PCRE stub function, it just dies with
>> +              * "cannot use Perl-compatible regexes[...]".
>> +              */
>>               opt->pcre1 = 1;
>
> Very well thought-out comment.  Our style wants you to have
> slash-aster that opens a multi-line comment on its own line, though.
Will fix.
>> +             opt->pcre2 = 0;
>> +#endif
>>               break;
>>       }
>>  }
>> @@ -446,6 +460,126 @@ static void free_pcre1_regexp(struct grep_pat *p)
>>  }
>>  #endif /* !USE_LIBPCRE1 */
>>
>> +#ifdef USE_LIBPCRE2
>> +static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt)
>> +{
>> +...
>> +     p->pcre2_pattern = pcre2_compile((PCRE2_SPTR)p->pattern,
>> +                                      p->patternlen, options, &error, &erroffset,
>> +                                      p->pcre2_compile_context);
>
> Are all die("BUG:...") in this function actual bugs, or just
> "die()"?  Just like the comment on an earlier patch, things like
> running out of memory that you as a Git programmer cannot fix by
> correcting this code are not die("BUG:"), but normal runtime errors.
Will fix these.
>> +
>> +     if (p->pcre2_pattern) {
>> +             p->pcre2_match_data = pcre2_match_data_create_from_pattern(p->pcre2_pattern, NULL);
>> +             if (!p->pcre2_match_data)
>> +                     die("BUG: Couldn't allocate PCRE2 match data");
>> +     } else {
>> +             pcre2_get_error_message(error, errbuf, sizeof(errbuf));
>> +             compile_regexp_failed(p, (const char *)&errbuf);
>> +     }
>> +
>> +     pcre2_config(PCRE2_CONFIG_JIT, &canjit);
>> +     if (canjit == 1) {
>> +             jitret = pcre2_jit_compile(p->pcre2_pattern, PCRE2_JIT_COMPLETE);
>> +             if (!jitret)
>> +                     p->pcre2_jit_on = 1;
>
> I think the same "would it be better to do this without canjit?"
> comment applies here.
Yup, changed.
>> +#else /* !USE_LIBPCRE2 */
>> +static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt)
>> +{
>> +     /* Unreachable until USE_LIBPCRE2 becomes synonymous with
>> +      * USE_LIBPCRE. See the sibling comment in
>> +      * grep_set_pattern_type_option().
>> +      */
>> +     die("cannot use Perl-compatible regexes when not compiled with USE_LIBPCRE");
>> +}
>
> Wow.  If I were doing this, I wouldn't have been this cautious, but
> I have no complaints ;-).
>