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From: "rearnsha at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/50883] [ARM] Suboptimal optimization for small structures
Date: Thu, 27 Oct 2011 16:53:00 -0000	[thread overview]
Message-ID: <bug-50883-4-9e9Txtn6iu@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-50883-4@http.gcc.gnu.org/bugzilla/>

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50883

Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW
                 CC|                            |rearnsha at gcc dot gnu.org

--- Comment #6 from Richard Earnshaw <rearnsha at gcc dot gnu.org> 2011-10-27 16:53:07 UTC ---
So for PPC, this seems to be a lucky side-effect of the way the PPC ABI is
defined.  On PPC the argument is passed by reference and the compiler generates
an initial load expression of X from memory (a callee copy).  The RTL
optimization passes are then (in combination with the subreg splitting code)
able to notice, somehow, that this is equivalent to the final result and to
make use of it.

On ARM the structure is passed by value and the argument expanding code
immediately tries to store a copy into the stack.  Then, rather than seeing
that this could be used from a register value it tries to work solely with the
stack copy.

I notice that neither architecture optimizes this if the struct is passed as an
address rather than by value.


  parent reply	other threads:[~2011-10-27 16:53 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-10-27 11:55 [Bug target/50883] New: " sebastian.huber@embedded-brains.de
2011-10-27 11:56 ` [Bug target/50883] " sebastian.huber@embedded-brains.de
2011-10-27 11:58 ` sebastian.huber@embedded-brains.de
2011-10-27 11:58 ` sebastian.huber@embedded-brains.de
2011-10-27 14:51 ` rguenth at gcc dot gnu.org
2011-10-27 15:20 ` sebastian.huber@embedded-brains.de
2011-10-27 16:53 ` rearnsha at gcc dot gnu.org [this message]
2022-02-04  0:50 ` pinskia at gcc dot gnu.org
2022-02-04  0:50 ` pinskia at gcc dot gnu.org
2022-02-04 11:05 ` rearnsha at gcc dot gnu.org
2022-02-04 11:11 ` pinskia at gcc dot gnu.org
2022-02-04 11:30 ` rguenth at gcc dot gnu.org
2022-02-04 11:45 ` ebotcazou at gcc dot gnu.org
2022-02-04 11:58 ` rguenther at suse dot de
2022-02-04 12:24 ` ebotcazou at gcc dot gnu.org
2022-02-04 12:27 ` rearnsha at gcc dot gnu.org
2022-02-04 12:29 ` rearnsha at gcc dot gnu.org
2022-02-04 12:55 ` ebotcazou at gcc dot gnu.org
2022-02-04 16:29 ` sebastian.huber@embedded-brains.de

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