From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-486892-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 88015 invoked by alias); 21 May 2015 08:46:05 -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 86660 invoked by uid 48); 21 May 2015 08:46:00 -0000
From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/66235] New: [SH] Optimize tst reg,const movrt sequence
Date: Thu, 21 May 2015 08:46:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 6.0
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: olegendo at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter target_milestone cf_gcctarget
Message-ID: <bug-66235-4@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: 2015-05/txt/msg01732.txt.bz2

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66235

            Bug ID: 66235
           Summary: [SH] Optimize tst reg,const movrt sequence
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org
  Target Milestone: ---
            Target: sh*-*-*

The following example:

bool test_00 (unsigned int x)
{
  return (x & 0x1042A) != 0;
}

compiled with -O2 -m4:

        mov.l   .L3,r1
        tst     r1,r4
        mov     #-1,r1
        rts
        negc    r1,r0
.L4:
        .align 2
.L3:
        .long   0x1042A

On non-SH2A there is no movrt insn and a !T -> reg move is done via negc.  If
the preceeding tst insn uses a constant, the constant can be complemented to
avoid the negc and #-1 constant load:

        mov.l   .L3,r1
        tst     r1,r4
        rts
        movt    r0
.L4:
        .align 2
.L3:
        .long   0xFFFEFBD5

The tstsi_t splitter could be extended to look for a following movrt insn and
optimize it accordingly.

The downside of doing this is an increased constant pool size, if the original
(non-complemented) constant is used for something else.  Moreover, it is only
beneficial to do this if there are no other negc #-1 movrt insns which share
the #-1 constant.  On the other hand, sharing the #-1 constant increases the
life time of regs and thus increases reg pressure.