[Bug other/66887] New: trunk/libmpx/mpxrt/mpxrt.c:158: possible performance problem

[Bug other/66887] New: trunk/libmpx/mpxrt/mpxrt.c:158: possible performance problem

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66887

            Bug ID: 66887
           Summary: trunk/libmpx/mpxrt/mpxrt.c:158: possible performance
                    problem
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com
  Target Milestone: ---

[trunk/libmpx/mpxrt/mpxrt.c:159]: (performance) Buffer 'buffer' is being
written before its old content has been used.

Source code is

  memset (buffer, 0, sizeof (buffer));
  memcpy (buffer,
      (uint8_t *)uctxt->uc_mcontext.fpregs + XSAVE_OFFSET_IN_FPMEM,
      sizeof (struct xsave_struct));

Maybe something like

  memcpy (buffer,
      (uint8_t *)uctxt->uc_mcontext.fpregs + XSAVE_OFFSET_IN_FPMEM,
      sizeof (struct xsave_struct));

  memset (&buffer[sizeof (struct xsave_struct))], 0, sizeof (buffer) - sizeof
(struct xsave_struct)) );

[Bug other/66887] trunk/libmpx/mpxrt/mpxrt.c:158: possible performance problem

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66887

--- Comment #1 from David Binderman <dcb314 at hotmail dot com> ---
sizeof (struct xsave_struct) is about 900 bytes, so there is plenty of time
to be saved.

[Bug other/66887] trunk/libmpx/mpxrt/mpxrt.c:158: possible performance problem

[ienkovich at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66887

Ilya Enkovich <ienkovich at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2015-09-24
                 CC|                            |ienkovich at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |ienkovich at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #2 from Ilya Enkovich <ienkovich at gcc dot gnu.org> ---
(In reply to David Binderman from comment #1)
> sizeof (struct xsave_struct) is about 900 bytes, so there is plenty of time
> to be saved.

Thanks for pointing at this.  Actually I don't see my we have both memset and
memcpy here.  Structure is copied just to return its field.  I'll fix it.

[Bug other/66887] trunk/libmpx/mpxrt/mpxrt.c:158: possible performance problem

[ienkovich at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66887

--- Comment #3 from Ilya Enkovich <ienkovich at gcc dot gnu.org> ---
Author: ienkovich
Date: Thu Oct 15 09:26:39 2015
New Revision: 228838

URL: https://gcc.gnu.org/viewcvs?rev=228838&root=gcc&view=rev
Log:
libmpx/

        PR other/66887
        * mpxrt/mpxrt.c (read_mpx_status_sig): Remove useless code.


Modified:
    trunk/libmpx/ChangeLog
    trunk/libmpx/mpxrt/mpxrt.c

[Bug other/66887] trunk/libmpx/mpxrt/mpxrt.c:158: possible performance problem

[ienkovich at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66887

Ilya Enkovich <ienkovich at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Ilya Enkovich <ienkovich at gcc dot gnu.org> ---
Fixed