From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-491383-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 21859 invoked by alias); 3 Jul 2015 14:40:59 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Received: (qmail 21805 invoked by uid 48); 3 Jul 2015 14:40:54 -0000
From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/66750] [4.9/5/6] Aggregate return not generated with -m32 -mregparm=3 or with -miamcu
Date: Fri, 03 Jul 2015 14:40:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 6.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: hjl.tools at gmail dot com
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution:
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 6.0
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields: bug_status cf_reconfirmed_on everconfirmed
Message-ID: <bug-66750-4-ijkt3bSayX@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-66750-4@http.gcc.gnu.org/bugzilla/>
References: <bug-66750-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2015-07/txt/msg00273.txt.bz2

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66750

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-07-03
     Ever confirmed|0                           |1

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
We have

'callee_pop_aggregate_return (NUMBER)'

     On x86-32 targets, you can use this attribute to control how
     aggregates are returned in memory.  If the caller is responsible
     for popping the hidden pointer together with the rest of the
     arguments, specify NUMBER equal to zero.  If callee is responsible
     for popping the hidden pointer, specify NUMBER equal to one.

     The default x86-32 ABI assumes that the callee pops the stack for
     hidden pointer.  However, on x86-32 Microsoft Windows targets, the
     compiler assumes that the caller pops the stack for hidden pointer.

and

static int
ix86_return_pops_args (tree fundecl, tree funtype, int size)
{
...
 /* Lose any fake structure return argument if it is passed on the stack.  */
  if (aggregate_value_p (TREE_TYPE (funtype), fundecl)
      && !ix86_keep_aggregate_return_pointer (funtype))
    {
      int nregs = ix86_function_regparm (funtype, fundecl);
      if (nregs == 0) 
        return GET_MODE_SIZE (Pmode);
    }

  return 0;
}

For -miamcu and -m64, ix86_return_pops_args always returns 0 since they
pass parameters in registers.  We have 2 choices:

1. Update IA MCU psABI to follow x86-64 psABI such that callee doesn't
pop the stack.
2. Update GCC to always pop stack for -m32.

I prefer #1.