[Bug c/36134] New: GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[Bug c/36134] New: GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[gunnar at greyhound-data dot com]

+++ This bug was initially created as a clone of Bug #36133 +++

Hello,

The ASM code created by GCC 4.2.1 for 68k/Coldfire platform is not optimal.
Comparing ASM output created by GCC 2.9 with GCC 4.2,
the generated code got partially much worse with GCC 4.


One problem that was visible a lot was that GCC used ADDA.L instead using the
shorter LEA instruction.

Please see the below example for details.
In line 28 and 2E you can see that two times the ADDA.L instructions was used,
where instead the shorter LEA instruction could have been used.



Example: C-source
Code:
void * copy_32x4a(void *destparam, const void *srcparam, size_t size)
{
        int *dest = destparam;
        const int *src = srcparam;
        int size32;
        size32 = size / 16;
        for (; size32; size32--) {
                *dest++ = *src++;
                *dest++ = *src++;
                *dest++ = *src++;
                *dest++ = *src++;
        }
}

Compile option: m68k-linux-gnu-gcc -mcpu=54455 -msoft-float -o example -Os
-fomit-frame-pointer example.c

Code generated by GCC 4.2:
04:       202f 000c       movel %sp@(12),%d0
08:       226f 0004       moveal %sp@(4),%a1
0c:       206f 0008       moveal %sp@(8),%a0
10:       e888            lsrl #4,%d0
12:       6022            bras 36
14:       2290            movel %a0@,%a1@
16:       2368 0004 0004  movel %a0@(4),%a1@(4)
1c:       2368 0008 0008  movel %a0@(8),%a1@(8)
22:       2368 000c 000c  movel %a0@(12),%a1@(12)
28:       d3fc 0000 0010  addal #16,%a1
2e:       d1fc 0000 0010  addal #16,%a0
34:       5380            subql #1,%d0
36:       4a80            tstl %d0
38:       66da            bnes 14
3a:       4e75            rts    

For comparison here is code that you would expect:
04:       202f 000c       movel %sp@(12),%d0
08:       226f 0004       moveal %sp@(4),%a1
0c:       206f 0008       moveal %sp@(8),%a0
10:       e888            lsrl #4,%d0
12:       6022            beq 20
14:       20d9            movel %a1@+,%a0@+
16:       20d9            movel %a1@+,%a0@+
18:       20d9            movel %a1@+,%a0@+
1a:       20d9            movel %a1@+,%a0@+
1c:       5380            subql #1,%d0
1e:       66da            bnes 14
20:       4e75            rts 

Compiler used:
m68k-linux-gnu-gcc -v
Using built-in specs.
Target: m68k-linux-gnu
Configured with: /scratch/shinwell/cf-fall-linux-lite/src/gcc-4.2/configure
--build=i686-pc-linux-gnu --host=i686-pc-linux-gnu --target=m68k-linux-gnu
--enable-threads --disable-libmudflap --disable-libssp --disable-libgomp
--disable-libstdcxx-pch --with-arch=cf --with-gnu-as --with-gnu-ld
--enable-languages=c,c++ --enable-shared --enable-symvers=gnu
--enable-__cxa_atexit --with-pkgversion=Sourcery G++ Lite 4.2-47
--with-bugurl=https://support.codesourcery.com/GNUToolchain/ --disable-nls
--prefix=/opt/freescale/usr/local/gcc-4.2.47-eglibc-2.5.47/m68k-linux
--with-sysroot=/opt/freescale/usr/local/gcc-4.2.47-eglibc-2.5.47/m68k-linux/m68k-linux-gnu/libc
--with-build-sysroot=/scratch/shinwell/cf-fall-linux-lite/install/m68k-linux-gnu/libc
--enable-poison-system-directories
--with-build-time-tools=/scratch/shinwell/cf-fall-linux-lite/install/m68k-linux-gnu/bin
--with-build-time-tools=/scratch/shinwell/cf-fall-linux-lite/install/m68k-linux-gnu/bin
Thread model: posix
gcc version 4.2.1 (Sourcery G++ Lite 4.2-47)


I hope that this report help you to improve the quality of GCC.

Kind regards

Gunnar von Boehn
--
P.S. I put the noticed issues in indivitual tivkets for easier tracking. I hope
that this is helpfull.


-- 
           Summary: GCC creates suboptimal ASM : usage of ADDA.L where LEA
                    could be used
           Product: gcc
           Version: 4.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: gunnar at greyhound-data dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: m68k-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134

[Bug target/36134] GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2008-05-07 19:33 -------
It would have been nice to check at least gcc 4.3 (or better current trunk).


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134

[Bug target/36134] GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[gunnar at greyhound-data dot com]

------- Comment #2 from gunnar at greyhound-data dot com  2008-05-28 16:18 -------
(In reply to comment #1)
> It would have been nice to check at least gcc 4.3 (or better current trunk).
> 

I've verified with latest source gcc source "version 4.4.0 20080523
(experimental) (GCC)" 

The most current GCC source still has the problem
that ADD.L instructions are used for incrementing pointers instead using
shorter LEA instruction.


Code generated by GCC 4.4 for the testcase.

copy_32x4:
        link.w %fp,#-12
        movem.l #3076,(%sp)
        move.l 16(%fp),%d2
        lsr.l #4,%d2
        move.l 8(%fp),%a3
        move.l 12(%fp),%a2
        jra .L6
.L7:
        move.l (%a2),%a1
        subq.l #1,%d2
        move.l 4(%a2),%d0
        move.l 8(%a2),%d1
        move.l 12(%a2),%a0
        add.l #16,%a2
        move.l %a1,(%a3)
        move.l %d0,4(%a3)
        move.l %d1,8(%a3)
        move.l %a0,12(%a3)
        add.l #16,%a3
.L6:
        tst.l %d2
        jne .L7
        movem.l (%sp),#3076
        unlk %fp
        rts



Regards
Gunnar


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134

[Bug target/36134] GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[gunnar at greyhound-data dot com]

------- Comment #3 from gunnar at greyhound-data dot com  2008-05-29 12:50 -------
Created an attachment (id=15699)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15699&action=view)
Prefer 4 byte long LEA over 6 byte long ADD.L

Please include the attached patch for GCC.

The added patch has changed the case statement to prefer the 4 byte long lea
over the 6 byte long add.l for immediate sub/add instructions to address
registers with an immediate operant size of 16bit max. 

LEA is optimized for pipelining (with destination forwarding) and is shorter
than ADD.L


Regards
Gunnar von Boehn


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134

[Bug target/36134] GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[schwab at suse dot de]

------- Comment #4 from schwab at suse dot de  2008-06-02 22:37 -------
Could you please submit your patch to gcc-patches@gcc.gnu.org, including a
ChangeLog entry and stating how you tested it.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134

[Bug target/36134] GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[gunnar at greyhound-data dot com]

------- Comment #5 from gunnar at greyhound-data dot com  2008-06-10 15:24 -------
(In reply to comment #4)
> Could you please submit your patch to gcc-patches@gcc.gnu.org, including a
> ChangeLog entry and stating how you tested it.
> 

As requested I did send the email last week.
Do you need anything else from me to work on this?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134

[Bug target/36134] GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[gunnar at greyhound-data dot com]

------- Comment #6 from gunnar at greyhound-data dot com  2008-06-12 14:27 -------
Andreas,

could you please have a look at this?

Cheers
Gunnar


-- 

gunnar at greyhound-data dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schwab at suse dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134

[Bug target/36134] GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[ams at gcc dot gnu dot org]

------- Comment #7 from ams at gcc dot gnu dot org  2008-11-14 10:50 -------
Subject: Bug 36134

Author: ams
Date: Fri Nov 14 10:49:06 2008
New Revision: 141853

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=141853
Log:
2008-11-14  Maxim Kuvyrkov  <maxim@codesourcery.com>
            Andrew Stubbs  <ams@codesourcery.com>
            Gunnar Von Boehn  <gunnar@genesi-usa.com>

        gcc/
        PR target/36134
        * config/m68k/m68k.md (addsi3_5200): Add a new alternative preferring
        the shorter LEA insn over ADD.L where possible.

        gcc/testsuite/
        PR target/36134
        * gcc.target/m68k/pr36134.c: New test.



Added:
    trunk/gcc/testsuite/gcc.target/m68k/pr36134.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/m68k/m68k.md
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134

[Bug target/36134] GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used

[ams at gcc dot gnu dot org]

------- Comment #8 from ams at gcc dot gnu dot org  2008-11-14 10:53 -------
The patch posted here has been accepted and committed:
http://gcc.gnu.org/ml/gcc-patches/2008-11/msg00581.html

This should resolve this issue.

Andrew


-- 

ams at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ams at gcc dot gnu dot org
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134