[Bug target/39501] New: -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[Bug target/39501] New: -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[martinwguy at yahoo dot it]

The following fragment when compiled -O -ffinite-math-only on arm-linux-gnueabi
should print 0.000000 but with gcc-4.1.2, 4.2.4, 4.3.3 it prints 99999.000000

#include <stdio.h>

#define test_min(x,y)   ((x) >  (y) ? (y) : (x))

int
main (void)
{
        static float data [1];
        float min = 99999.0 ;

        min = test_min (min, data[0]) ;

        printf("min = %f\n", min);

        return min != 0.0 ;
}

This only happens for floats, not doubles. The main difference in the asm is
that without -ffinite-math-only (working) it goes
        mov     r0, r4
        ldr     r1, .L6+4
        bl      __aeabi_fcmplt
        cmp     r0, #0
        ldr     r3, .L6+4
        moveq   r4, r3
        mov     r0, r4
while with -ffinite-math-only (broken) it goes
        ldr     r5, .L5+4
        mov     r0, r4
        mov     r1, r5
        bl      __aeabi_fcmple
        cmp     r0, #0
        movgt   r4, r5
        mov     r0, r4
I guess that should be moveq.

This makes libvorbis fail on arm-linux-gnueabi when using softfloat.
See https://trac.xiph.org/ticket/1526 for a longer code example failing on
min() and max().


-- 
           Summary: -O -ffinite-math-only gets min(x,y) optimization wrong
                    for SF on arm-*-gnueabi
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: martinwguy at yahoo dot it
GCC target triplet: arm-linux-gnueabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[ramana dot r at gmail dot com]

------- Comment #1 from ramana dot r at gmail dot com  2009-03-19 15:53 -------
Adding self to CC list - 

mainline is also broken. The only difference in mainline is that we generate a
movle instead of movgt.

It should indeed be a moveq instead of a movle.

cheers
Ramana


-- 

ramana dot r at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rearnsha at gcc dot gnu dot
                   |                            |org, ramana dot r at gmail
                   |                            |dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[ramana dot r at gmail dot com]

------- Comment #2 from ramana dot r at gmail dot com  2009-03-19 16:05 -------
Or get rid of the cmp. The Runtime ABI suggests that the Z,N,C flags are set
for the result of the comparison. If that is true then the second cmp is
unnecessary.

Table 5 section 4.1.2 of the ARM Runtime ABI suggests this.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[martinwguy at yahoo dot it]

------- Comment #3 from martinwguy at yahoo dot it  2009-03-19 16:29 -------
ramana:
I think you'll find the flags are only set for the 3-way comparisons.
__aeabi_cmple just returns 0 or 1
"Use for C <=" in the table means the C language, not the carry flag.

If you can find where the error is in the GCC source, that'd be great.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[ramana dot r at gmail dot com]

------- Comment #4 from ramana dot r at gmail dot com  2009-03-19 16:49 -------
(In reply to comment #3)
> ramana:
> I think you'll find the flags are only set for the 3-way comparisons.
> __aeabi_cmple just returns 0 or 1
> "Use for C <=" in the table means the C language, not the carry flag.
> If you can find where the error is in the GCC source, that'd be great.

It was pointed out that I was looking at the wrong function in the runtime ABI
- so I take that back. I was referring to the void __aeabi_cfcmple(float,
float) variant rather than the fcmple that's used in this case. 

So if you were to use the cfcmple variants (which gcc can't at the moment) the
extra cmp might be removed.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[rearnsha at gcc dot gnu dot org]

------- Comment #5 from rearnsha at gcc dot gnu dot org  2009-03-19 16:53 -------
Also affects all other EABI target builds.

THe bug is in movsfcc (and movdfcc) which have not been corrected to account
for the libcall comparisons returning a bool value in the EABI.

I'm currently testing a fix


-- 

rearnsha at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rearnsha at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
           Priority|P3                          |P2
   Last reconfirmed|0000-00-00 00:00:00         |2009-03-19 16:53:01
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[rearnsha at gcc dot gnu dot org]

------- Comment #6 from rearnsha at gcc dot gnu dot org  2009-03-19 17:02 -------
Correction: it doesn't affect movdfcc since that only matches on hard-float
targets.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2009-03-19 18:17 -------
*** Bug 39507 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kurt at roeckx dot be


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for SF on arm-*-gnueabi

[martinwguy at yahoo dot it]

------- Comment #8 from martinwguy at yahoo dot it  2009-03-29 17:49 -------
A bit more info on the real-world cases that this bug bites.

1) libvorbis's testsuite (only in trunk) fails:

    svn co http://svn.xiph.org/trunk/vorbis
    cd vorbis; ./autogen.sh; ./configure; make
    test/test

complains that "max_abs (0.000000) too small."; it should say "ok"

It can be fixed by using "./configure CFLAGS=-fno-finite-math-only"

(Both of these utilities' build scripts append your CFLAGS settings to their
own default ones.)

2) LAME -V0 outputs silence

    wget http://downloads.sourceforge.net/lame/lame-398-2.tar.gz
    tar xzf lame-398-2.tar.gz
    cd lame-398-2
    ./configure && make
    wget http://martinwguy.co.uk/martin/test/Happy.wav
    frontend/lame --nohist -V0 Happy.wav Happy.mp3
    mpg123 -w Happy2.wav Happy.mp3
    # Or frontend/lame --quiet --decode Happy.mp3 Happy2.wav
    sox Happy2.wav -e stat | grep 'Maximum amplitude'

should say something like maxamp = 0.574310, not 0.000000

It can be fixed by using
        "./configure CFLAGS=-fno-finite-math-only"
and also with
        "./configure CFLAGS="-fno-schedule-insns -fno-schedule-insns2"
though this does not fix the libvorbis issue.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[rearnsha at gcc dot gnu dot org]

------- Comment #9 from rearnsha at gcc dot gnu dot org  2009-04-04 10:37 -------
Subject: Bug 39501

Author: rearnsha
Date: Sat Apr  4 10:37:10 2009
New Revision: 145534

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=145534
Log:
        PR target/39501
        * arm.md (movsfcc): Disable if not TARGET_HARD_FLOAT.
        * testsuite/gcc.c-torture/execute/pr39501.c: New file.
        * testsuite/gcc.c-torture/execute/pr39501.x: New file.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr39501.c
    trunk/gcc/testsuite/gcc.c-torture/execute/pr39501.x
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/arm/arm.md


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[martinwguy at yahoo dot it]

------- Comment #10 from martinwguy at yahoo dot it  2009-04-04 11:23 -------
Is that *it*? Disable movsfcc completely without finding the cause of the
specific failure?
No wonder the generated ARM code is bigger, slower and buggier with every
release!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[martinwguy at yahoo dot it]

------- Comment #11 from martinwguy at yahoo dot it  2009-04-04 11:50 -------
Sorry about that. I've now seen
http://gcc.gnu.org/ml/gcc-patches/2009-04/msg00300.html

    M


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[steven at gcc dot gnu dot org]

------- Comment #12 from steven at gcc dot gnu dot org  2009-04-04 11:53 -------
Re. comment #10: And who are you funding, Martin Guy, to improve GCC for ARM?
Or are you just another user who expects magic for free?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[steven at gcc dot gnu dot org]

------- Comment #13 from steven at gcc dot gnu dot org  2009-04-04 12:00 -------
Re. comment #10: I don't know about the "buggier" and "slower" parts.

But for "bigger" I know we have benchmarks that say otherwise. e.g. CSiBE for
arm-elf (http://www.inf.u-szeged.hu/csibe/s-arm.php) and CSiBE for arm-linux
(http://www.inf.u-szeged.hu/csibe/s-arm-linux.php, unfortunately stopped
running in 2006 due to -- you've guessed it -- lack of funding).

Obviously there's no denying that GCC still is too far behind most commercial
compilers for ARM...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[rearnsha at gcc dot gnu dot org]

------- Comment #14 from rearnsha at gcc dot gnu dot org  2009-04-04 12:25 -------
Subject: Bug 39501

Author: rearnsha
Date: Sat Apr  4 12:25:06 2009
New Revision: 145537

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=145537
Log:
        PR target/39501
        * arm.md (movsfcc): Disable if not TARGET_HARD_FLOAT.
        * testsuite/gcc.c-torture/execute/pr39501.c: New file.
        * testsuite/gcc.c-torture/execute/pr39501.x: New file.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/gcc.c-torture/execute/pr39501.c
    branches/gcc-4_4-branch/gcc/testsuite/gcc.c-torture/execute/pr39501.x
Modified:
    branches/gcc-4_4-branch/gcc/ChangeLog
    branches/gcc-4_4-branch/gcc/config/arm/arm.md


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[rearnsha at gcc dot gnu dot org]

------- Comment #15 from rearnsha at gcc dot gnu dot org  2009-05-16 22:25 -------
Subject: Bug 39501

Author: rearnsha
Date: Sat May 16 22:24:59 2009
New Revision: 147623

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=147623
Log:
        PR target/39501
        * arm.md (movsfcc): Disable if not TARGET_HARD_FLOAT.
        * testsuite/gcc.c-torture/execute/pr39501.c: New file.
        * testsuite/gcc.c-torture/execute/pr39501.x: New file.

Added:
    branches/gcc-4_3-branch/gcc/testsuite/gcc.c-torture/execute/pr39501.c
    branches/gcc-4_3-branch/gcc/testsuite/gcc.c-torture/execute/pr39501.x
Modified:
    branches/gcc-4_3-branch/gcc/ChangeLog
    branches/gcc-4_3-branch/gcc/config/arm/arm.md


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[ramana at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |4.3.4

--- Comment #18 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> ---
fixed.

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[martinwguy at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

--- Comment #17 from Martin Guy <martinwguy at gmail dot com> 2010-12-03 14:46:28 UTC ---
Sort of. The cause of the bug was never found, and the workaround is to disable
an instruction.  It might be worth trying enabling movsfcc in current GCC and
re-running the tests, since the conditional execution stuff in the middle end
was rewritten between 4.3 and 4.4 if I remember correctly, so the actual bug in
the middle end may have gone away with that rewrite.

[Bug target/39501] -O -ffinite-math-only gets min(x,y) optimization wrong for soft-float on arm-*-gnueabi

[ramana at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39501

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ramana at gcc dot gnu.org
      Known to fail|                            |

--- Comment #16 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> 2010-12-03 11:04:06 UTC ---
Isn't this now fixed ? 

Ramana