[Bug analyzer/107943] [11/12/13 Regression] gcc -fanalyzer hangs in openssl curve25519.c since r11-3840-gaf66094d03779377

[bernd.edlinger at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107943

--- Comment #6 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
I don't know if that is relevant or not,
but I was using a slighthly different criterion in bisection.
I used .../configure --prefix=... --enable-languages=all
and defined the bad criterion using the unreduced test case
compilation took >10 minutes on Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz
The original test case is available as follows:

$ wget https://www.openssl.org/source/openssl-1.1.1s.tar.gz
$ tar xf openssl-1.1.1s.tar.gz
$ ./config -fanalyzer
$ make

With this pointed to a different commit:
r12-7615-gc5288df751f

Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Fri Mar 11 17:46:50 2022 +0000

    PR tree-optimization/98335: Improvements to DSE's compute_trims.

    This patch is the main middle-end piece of a fix for PR tree-opt/98335,
    which is a code-quality regression affecting mainline.  The issue occurs
    in DSE's (dead store elimination's) compute_trims function that determines
    where a store to memory can be trimmed.  In the testcase given in the
    PR, this function notices that the first byte of a DImode store is dead,
    and replaces the 8-byte store at (aligned) offset zero, with a 7-byte store
    at (unaligned) offset one.  Most architectures can store a power-of-two
    bytes (up to a maximum) in single instruction, so writing 7 bytes requires
    more instructions than writing 8 bytes.  This patch follows Jakub Jelinek's
    suggestion in comment 5, that compute_trims needs improved heuristics.

beginning with this version the original test case, enters
a steady state after 2 minutes (observed with top:
VIRT=196296 RES=170872 SHR=21992  %CPU=100,0) and has no
progress for at least 20 hours, before I killed it.
The reduced test case does not exhibit this behaviour,
and runs just for some seconds.

But I agree that the r11-3840-gaf66094d03779377 is also special
and made the compile time raise from 0 to 2-10 minutes, however
I would not have opened this issue for that, since I was believing
there is something expensive to check that just did not give
a result in the end.