[Bug gdb/30934] New: Stopping at a breakpoint takes minutes if a source file has long lines

["hi-angel at yandex dot ru" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30934

            Bug ID: 30934
           Summary: Stopping at a breakpoint takes minutes if a source
                    file has long lines
           Product: gdb
           Version: 13.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: hi-angel at yandex dot ru
  Target Milestone: ---

Created attachment 15149
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15149&action=edit
testcase

No idea why it's taking so long, given I do not execute any commands that would
trigger showing these long lines, but debugging such a file with gdb is nigh
impossible. After showing an initial message that it's about to stop on a
breakpoint it just hangs for many minutes with 100% CPU load.

# Steps to reproduce

1. Download the attached file
2. Run commands:

    $ g++ test.cpp -o a -g3 -O0
    $ gdb -q --nx ./a
    Reading symbols from ./a...
    (gdb) br 56
    Breakpoint 1 at 0x1564: file test.cpp, line 56.
    (gdb) r
    Starting program: /tmp/a

    This GDB supports auto-downloading debuginfo from the following URLs:
      <https://debuginfod.archlinux.org>
    Enable debuginfod for this session? (y or [n])
    Debuginfod has been disabled.
    To make this setting permanent, add 'set debuginfod enabled off' to
.gdbinit.
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/usr/lib/libthread_db.so.1".

    Breakpoint 1, Solution::numOfSubarrays (this=0x7ffffff9c076,
arr=std::vector of length 100000, capacity 100000 = {...}) at test.cpp:56

## Expected

After stopping at breakpoint 1 it immediately gives the prompt for typing
further commands

## Actual

It the `Breakpoint 1` text appears, it just hangs for many minutes.

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