Horton

Re: Some regular-expression performance hacking

Andres Freund <andres@anarazel.de>

View thread View on postgr.es
From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2021-02-23T18:18:51Z
Lists: pgsql-hackers 
On 2021-02-23 13:09:18 -0500, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > One of the recent commits have introduce a new warning with gcc 10, when
> > building with optimizations:
>
> Oddly, I see no such warning with Fedora's current compiler,
> gcc version 10.2.1 20201125 (Red Hat 10.2.1-9) (GCC)
>
> Are you using any special compiler switches?

A few. At first I didn't see any relevant ones - but I think it's just
that you need to use -O3 instead of -O2.

andres@awork3:~/build/postgres/dev-optimize/vpath$ (cd src/backend/regex/ && ccache gcc-10 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wimplicit-fallthrough=3 -Wcast-function-type -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -I../../../src/include -I/home/andres/src/postgresql/src/include  -D_GNU_SOURCE -I/usr/include/libxml2   -c -o regcomp.o /home/andres/src/postgresql/src/backend/regex/regcomp.c -O2)

andres@awork3:~/build/postgres/dev-optimize/vpath$ (cd src/backend/regex/ && ccache gcc-10 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wimplicit-fallthrough=3 -Wcast-function-type -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -I../../../src/include -I/home/andres/src/postgresql/src/include  -D_GNU_SOURCE -I/usr/include/libxml2   -c -o regcomp.o /home/andres/src/postgresql/src/backend/regex/regcomp.c -O3)
In file included from /home/andres/src/postgresql/src/backend/regex/regcomp.c:2304:
/home/andres/src/postgresql/src/backend/regex/regc_nfa.c: In function ‘checkmatchall’:
/home/andres/src/postgresql/src/backend/regex/regc_nfa.c:3086:20: warning: array subscript -1 is outside array bounds of ‘_Bool[257]’ [-Warray-bounds]
 3086 |    hasmatch[depth] = true;
      |                    ^
/home/andres/src/postgresql/src/backend/regex/regc_nfa.c:2920:8: note: while referencing ‘hasmatch’
 2920 |  bool  hasmatch[DUPINF + 1];
      |        ^~~~~~~~

andres@awork3:~/build/postgres/dev-optimize/vpath$ gcc-10 --version
gcc-10 (Debian 10.2.1-6) 10.2.1 20210110
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Greetings,

Andres Freund

Commits

  1. Suppress unnecessary regex subre nodes in a couple more cases.

  2. Improve memory management in regex compiler.

  3. Extend a test case a little

  4. Allow complemented character class escapes within regex brackets.

  5. Suppress compiler warning in new regex match-all detection code.

  6. Avoid generating extra subre tree nodes for capturing parentheses.

  7. Convert regex engine's subre tree from binary to N-ary style.

  8. Fix regex engine to suppress useless concatenation sub-REs.

  9. Recognize "match-all" NFAs within the regex engine.

  10. Invent "rainbow" arcs within the regex engine.

  11. Make some minor improvements in the regex code.

  12. Display the time when the process started waiting for the lock, in pg_locks, take 2

  13. README/C-comment: document GiST's NSN value

  14. doc: Mention NO DEPENDS ON EXTENSION in its supported ALTER commands