[Bug gdb/27979] New: Performance regression of ~10% in conditional breakpoint testcase

[Bug gdb/27979] New: Performance regression of ~10% in conditional breakpoint testcase

[mhov at undo dot io]

https://sourceware.org/bugzilla/show_bug.cgi?id=27979

            Bug ID: 27979
           Summary: Performance regression of ~10% in conditional
                    breakpoint testcase
           Product: gdb
           Version: 10.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: mhov at undo dot io
  Target Milestone: ---

Created attachment 13491
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13491&action=edit
reproducer program

There seems to be a performance regression from 9.2 to 10.2 that is observable
in the time to run the following command on the attached reproducer program.
This has been used to benchmark the performance of conditional breakpoints.

  $ gcc --version
    gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
  $ gcc -g repro.c
  $ ./gdb --batch --ex "b foo if bar==0x7ffffff" --ex "run" --args ./a.out

Also attached is a log from the libera.chat #gdb channel where this regression
was discussed.

As can be seen in the attached chat log, bisection by Simon suggests that this
commit is to blame:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1009d92fc621bc4d017029b90a5bfab16e17fde5

I'm not currently in a position to delve deeper into this, so I'm posting here
in case anyone wants to pick it up.

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[Bug gdb/27979] Performance regression of ~10% in conditional breakpoint testcase

[mhov at undo dot io]

https://sourceware.org/bugzilla/show_bug.cgi?id=27979

--- Comment #1 from Magne Hov <mhov at undo dot io> ---
Created attachment 13492
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13492&action=edit
#gdb chatlog

Attached chatlog

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[Bug gdb/27979] Performance regression of ~10% in conditional breakpoint testcase

[mhov at undo dot io]

https://sourceware.org/bugzilla/show_bug.cgi?id=27979

Magne Hov <mhov at undo dot io> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|10.1                        |HEAD

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[Bug gdb/27979] Performance regression of ~10% in conditional breakpoint testcase

[simark at simark dot ca]

https://sourceware.org/bugzilla/show_bug.cgi?id=27979

Simon Marchi <simark at simark dot ca> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |simark at simark dot ca

--- Comment #2 from Simon Marchi <simark at simark dot ca> ---
Things to investigate:

 - We do a lot of work finding tailcalls even though no tailcalls are involved
the test case.  Is there a way we can do less work in this case?
 - On the fast path, while looking for tailcalls, a NO_ENTRY_VALUE_ERROR
exception is thrown.  It's probably not good to rely on exceptions being thrown
in the normal path of the program, maybe try to change that with functions
returning nullptr if they don't find anything.

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[Bug gdb/27979] Performance regression of ~10% in conditional breakpoint testcase

[ssbssa at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=27979

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ssbssa at sourceware dot org

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