[Bug c/48783] New: ARM: kernel compiled at -O2 has a unused reference to __aeabi_uldivmod

[Bug c/48783] New: ARM: kernel compiled at -O2 has a unused reference to __aeabi_uldivmod

[michael.hope at linaro dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

           Summary: ARM: kernel compiled at -O2 has a unused reference to
                    __aeabi_uldivmod
           Product: gcc
           Version: 4.5.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: michael.hope@linaro.org


Created attachment 24107
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24107
Preprocessed source

When compiled, the attached code refers to the 64 bit unsigned divmod helper
function '__aeabi_uldivmod' even though the function is never called.  This
causes a link error when cross-compiling an ARM Linux 2.6.38 kernel.

To reproduce:
 * Make a arm-linux-gnueabi cross compiler configured with --with-mode=thumb
--with-arch=armv7-a --with-tune=cortex-a9 --with-float=softfp --with-fpu=neon
 * Compile the attached code with 'arm-linux-gnueabi-gcc -O2 -S wm8974.i'
 * See a '.global __aeabi_uldivmod' in the header of wm8974_set_dai_pll

Marking pll_factors() as noinline or putting asm("" : "+r"(source)); before the
call to do_div() works around the problem.

[Bug c/48783] ARM: kernel compiled at -O2 has a unused reference to __aeabi_uldivmod

[ams at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

Andrew Stubbs <ams at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ams at gcc dot gnu.org

--- Comment #1 from Andrew Stubbs <ams at gcc dot gnu.org> 2011-04-27 09:15:08 UTC ---
I don't see any call to __aeabi_uldivmod???

I *do* see __aeabi_uidivmod, and that does seem to be called properly.

I get:

        .global __aeabi_uidiv                                                   
        .global __aeabi_uidivmod                                                
        .align  2
        .thumb                                                                  
        .thumb_func                                                             
        .type   pll_factors, %function
pll_factors:                                                                    
        .fnstart
[.....]                                                        
.L54:   
        ldrb    r3, [r6, #0]    @ zero_extendqisi2
        mov     r0, r7
        mov     r1, r4
        bfi     r3, r5, #1, #4
        strb    r3, [r6, #0]
        bl      __aeabi_uidivmod
        movw    r5, #52429
        movt    r5, 52428
        mov     r0, #167772160
        umull   r0, r1, r1, r0
[.....]

I can't find a bug here?

[Bug c/48783] ARM: kernel compiled at -O2 has a unused reference to __aeabi_uldivmod

[michael.hope at linaro dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

--- Comment #2 from Michael Hope <michael.hope at linaro dot org> 2011-04-27 09:52:09 UTC ---
Sorry, the original attachment included the __attribute__((noinline))
workaround on pll_factors().  Attached is the original that shows the fault.

[Bug c/48783] ARM: kernel compiled at -O2 has a unused reference to __aeabi_uldivmod

[michael.hope at linaro dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

--- Comment #3 from Michael Hope <michael.hope at linaro dot org> 2011-04-27 09:54:56 UTC ---
Created attachment 24111
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24111
Preprocessed source

[Bug c/48783] ARM: kernel compiled at -O2 has a unused reference to __aeabi_uldivmod

[ams at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

--- Comment #4 from Andrew Stubbs <ams at gcc dot gnu.org> 2011-04-27 11:08:10 UTC ---
Somewhat reduced testcase:

static void
f (unsigned int a)
{
  unsigned long long __res;
  if (~0ULL % (a / (a & -a)) == 0)
    { 
      asm ("": "+&r" (__res));
    }
}

int
g (unsigned int a)
{
  f (a);
}


This gives:

        .global __aeabi_uidiv
        .global __aeabi_uldivmod
        .text
        .align  2
        .global g
        .thumb
        .thumb_func
        .type   g, %function
g:
        .fnstart
.LFB1:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        push    {lr}
        .save {lr}
        ldr     pc, [sp], #4
        .fnend

So, both __aeabi_uidiv and __aeabi_uldivmod are declared global, but neither is
actually used as the code is optimized away.

[Bug c/48783] ARM: kernel compiled at -O2 has a unused reference to __aeabi_uldivmod

[ramana at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.05.31 22:28:11
                 CC|                            |ramana at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #5 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> 2011-05-31 22:28:11 UTC ---
IIUC the problem is because we externalize the label before the functions have
been deleted. 

Based on a quick look at the sources, I *think* this comes from the fact that
the default definition of ASM_OUTPUT_EXTERNAL_LIBCALL ends up generating a
.globl symname and somehow don't think this is a port specific problem ( which
I *think* comes from config/elfos.h )


cheers
Ramana

[Bug tree-optimization/48783] ~0ULL % (a / (a & -a)) == 0 is not optimized to false on the tree level

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization, TREE
             Target|Arm                         |
   Last reconfirmed|2011-05-31 22:28:11         |2012-01-28
          Component|c                           |tree-optimization
            Summary|ARM: kernel compiled at -O2 |~0ULL % (a / (a & -a)) == 0
                   |has a unused reference to   |is not optimized to false
                   |__aeabi_uldivmod            |on the tree level

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-01-29 01:44:28 UTC ---
~0ULL % (a / (a & -a)) == 0
Is not optimized to false on the tree level.

Basically we should figure that out and we would then remove the reference to
the uldivmod libcall.

[Bug tree-optimization/48783] ~0ULL % (a / (a & -a)) == 0 is not optimized to false on the tree level

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |5.1.0

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note the reduced testcase in comment #4 has been fixed since GCC 5 but I think
the original issue is still there ...

[Bug tree-optimization/48783] ~0ULL % (a / (a & -a)) == 0 is not optimized to false on the tree level

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
See also thread starting at
https://inbox.sourceware.org/gcc-patches/20221208105944.660323-1-jose.marchesi@oracle.com/
.

[Bug tree-optimization/48783] ~0ULL % (a / (a & -a)) == 0 is not optimized to false on the tree level

[jemarch at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783

Jose E. Marchesi <jemarch at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jemarch at gcc dot gnu.org

--- Comment #9 from Jose E. Marchesi <jemarch at gcc dot gnu.org> ---
Note https://gcc.gnu.org/pipermail/gcc-patches/2023-August/627864.html