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* [Bug ipa/106809] New: [12 regression] large bison grammars compilation got a lot slower, mainly due to -Wuninitialized
@ 2022-09-01 23:42 andres at anarazel dot de
  2022-09-02  6:42 ` [Bug tree-optimization/106809] " rguenth at gcc dot gnu.org
                   ` (13 more replies)
  0 siblings, 14 replies; 15+ messages in thread
From: andres at anarazel dot de @ 2022-09-01 23:42 UTC (permalink / raw)
  To: gcc-bugs

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

^ permalink raw reply	[flat|nested] 15+ messages in thread
end of thread, other threads:[~2023-02-07 12:33 UTC | newest]

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2022-09-01 23:42 [Bug ipa/106809] New: [12 regression] large bison grammars compilation got a lot slower, mainly due to -Wuninitialized andres at anarazel dot de
2022-09-02  6:42 ` [Bug tree-optimization/106809] " rguenth at gcc dot gnu.org
2022-09-02  7:04 ` [Bug tree-optimization/106809] [12/13 " rguenth at gcc dot gnu.org
2022-09-02  7:12 ` rguenth at gcc dot gnu.org
2022-09-02  7:16 ` marxin at gcc dot gnu.org
2022-09-02  8:31 ` rguenth at gcc dot gnu.org
2022-09-02  8:32 ` rguenth at gcc dot gnu.org
2022-09-02 11:44 ` rguenth at gcc dot gnu.org
2022-09-02 12:13 ` rguenth at gcc dot gnu.org
2022-09-02 12:33 ` cvs-commit at gcc dot gnu.org
2022-09-02 12:33 ` [Bug tree-optimization/106809] [12 " rguenth at gcc dot gnu.org
2022-09-09  9:49 ` cvs-commit at gcc dot gnu.org
2022-09-09  9:50 ` rguenth at gcc dot gnu.org
2023-02-07 12:00 ` cvs-commit at gcc dot gnu.org
2023-02-07 12:33 ` cvs-commit at gcc dot gnu.org

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