https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106809
Bug ID: 106809
Summary: [12 regression] large bison grammars compilation got a
lot slower, mainly due to -Wuninitialized
Product: gcc
Version: 12.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: andres at anarazel dot de
CC: marxin at gcc dot gnu.org
Target Milestone: ---
Created attachment 53529
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53529&action=edit
preprocessed input file showing slowdown
Hi,
I noticed that building the .c output from bison got a lot slower in 12,
compared to 11.
$ gcc-12 --version
gcc-12 (Debian 12.2.0-1) 12.2.0
Copyright (C) 2022 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.
$ gcc-12 preproc.i -c -Wuninitialized
real 0m3.558s
user 0m3.475s
sys 0m0.083s
$ time gcc-11 preproc.i -c -Wuninitialized
real 0m1.232s
user 0m1.150s
sys 0m0.082s
This is a pretty egregious case, for saner grammars the performance difference
is smaller.
There's also a performance difference without -Wuninitialized, but it's much
smaller (1.090s -> 1.314s)
Looking at -ftime-report, there's a very clear difference in how much time is
spent in "uninit var analysis"
11: uninit var analysis : 0.01 ( 1%) 0.00 ( 0%) 0.00 (
0%) 10k ( 0%)
12: uninit var analysis : 2.24 ( 63%) 0.00 ( 0%) 2.26 (
55%) 393k ( 1%)
Regards,
andres
