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From: "eggert at cs dot ucla.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug analyzer/107060] New: -fanalyzer unbearably slow when compiling
 GNU Emacs
Date: Tue, 27 Sep 2022 19:20:09 +0000
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X-Bugzilla-Version: 12.2.1
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107060

            Bug ID: 107060
           Summary: -fanalyzer unbearably slow when compiling GNU Emacs
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: eggert at cs dot ucla.edu
  Target Milestone: ---

Created attachment 53634
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D53634&action=3Dedit
compressed source file that gcc -S -fanalyzer -O2 compiles verrrry slowly

For a while, gcc -fanalyzer has been so unbearably slow when compiling GNU
Emacs that we Emacs developers disable -fanalyzer unless the builder
specifically asks for it, which almost nobody does because it's sooo slow. I
haven't bothered to file a bug report because I assumed the analyzer code w=
as
still being worked on and tuned, but I just now tried -fanalyzer again on a=
 new
machine and it was still so slow that I am finally filing a bug report.

The biggest pole in the tent is when gcc compiles Emacs's xdisp.c file, whi=
ch
is large for Emacs (38 Klines) but not that large. I am attaching the
preprocessed output as the file u.i.gz. Compile it with:

gzip -d u.i
gcc -S -fanalyzer -O2 u.i

On my older Fedora 36 desktop (AMD Phenom II X4 910e) with gcc (GCC) 12.2.1
20220819 (Red Hat 12.2.1-2) GCC takes 12 minutes 3 seconds, which is
ridiculous. On my newer Ubuntu 22.04 desktop (Intel Xeon W-1350) with gcc-12
(Ubuntu 12.1.0-2ubuntu1~22.04) 12.1.0, GCC takes 3 minutes 43 seconds, whic=
h is
still way too long.

Could you please take a look at this test case and see what's slowing down
-fanalyzer? If you can't improve GCC, is there some easy way we Emacs
developers can rewrite the source to avoid the performance issue, whatever =
it
is? Thanks.=