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bug#21513: (now an infinite loop in grep/tests/triple-backref?)

From: Paul Eggert
Subject: bug#21513: (now an infinite loop in grep/tests/triple-backref?)
Date: Sat, 18 Jan 2020 14:16:45 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 1/18/20 6:44 AM, Martin Liška wrote:
I can confirm that it never finishes on i586.

I can't reproduce the problem, either on Ubuntu 18.04.3 x86-64 (GCC Ubuntu 7.4.0-1ubuntu1~18.04.1) or on Fedora 31 (GCC 9.2.1 20190827 x86-64 (Red Hat 9.2.1-1)). I did what should have been the equivalent of:

git clone https://git.savannah.gnu.org/git/grep.git
# This is commit 23bf27015e0cc45d0012f54b8e24ac19fdca89f7.
cd grep
./configure --with-included-regex CC='gcc -m32'
make check

and it worked for me; the triple-backref test had an XFAIL and did not loop. Can you send me more-detailed instructions for how to reproduce the bug?

I would recommend to replace   DEBUG_ASSERT (num >= 0);
which expands to:
   ((num >= 0) ? (void) 0 : __builtin_unreachable ());


   if (num < 0)
     __builtin_abort ();

The regexec.c code doesn't abort, I guess under the theory that one is supposed to fix the code than insert runtime assertions that slow things down. You can compile with -DDEBUG if you want it to abort, but be prepared for other grep tests to fail if you do so. Admittedly this is a messy area.

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