From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id BA29F385AC12; Sun, 22 Aug 2021 08:47:48 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org BA29F385AC12
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/87238] Redundant Restore of $x0 when memcpy
 always returns the first argument.
Date: Sun, 22 Aug 2021 08:47:48 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 7.3.0
X-Bugzilla-Keywords: missed-optimization, ra
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
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: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: keywords
Message-ID: <bug-87238-4-VWKrrPk8a0@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-87238-4@http.gcc.gnu.org/bugzilla/>
References: <bug-87238-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Sun, 22 Aug 2021 08:47:48 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D87238

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ra

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note I had to change the testcase to be using size 128.

But this is interesting, IRA was able to figure the memset return value:
(call_insn 14 13 17 2 (parallel [
            (set (reg:DI 0 x0)
                (call (mem:DI (symbol_ref:DI ("memcpy") [flags 0x41]=20
<function_decl 0x7efee90fd200 __builtin_memcpy>) [0 __builtin_memcpy S8 A8])
                    (const_int 0 [0])))
            (unspec:DI [
                    (const_int 0 [0])
                ] UNSPEC_CALLEE_ABI)
            (clobber (reg:DI 30 x30))
        ]) "/app/example.cpp":10:16 47 {*call_value_insn}
     (expr_list:REG_RETURNED (reg/f:DI 95)
        (expr_list:REG_DEAD (reg:DI 2 x2)
            (expr_list:REG_DEAD (reg:DI 1 x1)
                (expr_list:REG_UNUSED (reg:DI 0 x0)
                    (expr_list:REG_CALL_DECL (symbol_ref:DI ("memcpy") [fla=
gs
0x41]  <function_decl 0x7efee90fd200 __builtin_memcpy>)
                        (expr_list:REG_EH_REGION (const_int 0 [0])
                            (nil)))))))
    (expr_list (clobber (reg:DI 17 x17))
        (expr_list (clobber (reg:DI 16 x16))
            (expr_list:DI (set (reg:DI 0 x0)
                    (reg:DI 0 x0))
                (expr_list:DI (use (reg:DI 0 x0))
                    (expr_list:DI (use (reg:DI 1 x1))
                        (expr_list:DI (use (reg:DI 2 x2))
                            (nil))))))))
(insn 17 14 18 2 (set (reg:DI 0 x0)
        (reg/f:DI 95)) "/app/example.cpp":10:16 53 {*movdi_aarch64}
     (expr_list:REG_DEAD (reg/f:DI 95)
        (expr_list:REG_EQUAL (plus:DI (reg/f:DI 64 sfp)
                (const_int -512 [0xfffffffffffffe00]))
            (nil))))

But not actually use it.

REG_RETURNED (reg/f:DI 95)

Instead if used the REG_EQUAL ....=