[Bug target/45000] New: RX signed extened unsigned char or short return value.

[Bug target/45000] New: RX signed extened unsigned char or short return value.

[kazuhiro dot inaoka dot ud at renesas dot com]

When a function return type is "unsigned char", the return value is sign
extended by "MOV" instruction.
It should be "MOVU" instruction.

ex)
unsigned char uA;

unsigned char
func()
{
  return uA;
}

NG)
_func:
        mov.L   #_uA, r14
        mov.B   [r14], r1
        rts
        .size   _func, .-_func
        .comm   _uA,1,4


-- 
           Summary: RX signed extened unsigned char or short return value.
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazuhiro dot inaoka dot ud at renesas dot com
 GCC build triplet: i686-linux
  GCC host triplet: i686-linux
GCC target triplet: rx-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45000

[Bug target/45000] RX signed extened unsigned char or short return value.

[nickc at redhat dot com]

------- Comment #1 from nickc at redhat dot com  2010-07-22 09:42 -------
Hi Kazuhiro-san,

This is not a bug, it is the expected behaviour.

 What is happening is that the return value from func() is being promoted to
"signed int" (and not "unsigned int" as you might expect).  Thus since the
MOV.B instruction performs a sign extension it is a sufficient instruction for
the load operation.

 Note - if you try using the result of calling func() then you will see a zero
extension being performed.  Eg:

 int bar (int a) { return a < func(); }

results in:

       mov.L   #_uA, r14
       movu.B  [r14], r14
       cmp     r1, r14
       sclt.L  r1
       rts

with inlining, or:

       push.l  r7
       mov.L   r1, r7
       bsr     _func
       movu.B  r1, r1
       cmp     r7, r1
       sclt.L  r1
       rtsd    #4, r7-r7

without.

Cheers
 Nick Clifton

PS. See section 6.3.1.1 of the ISO C99 standard for more information about this
behaviour


-- 

nickc at redhat dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nickc at redhat dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45000

[Bug target/45000] RX signed extened unsigned char or short return value.

[kazuhiro dot inaoka dot ud at renesas dot com]

------- Comment #2 from kazuhiro dot inaoka dot ud at renesas dot com  2010-07-28 07:19 -------
(In reply to comment #1)
Hi Nick

Thank you for your reply.

Your example is OK. 
But I'm not clear.

> extension being performed.  Eg:
>  int bar (int a) { return a < func(); }
If the func() is external function, output code is the following.
_bar:
 push.l r7
 mov.L  r1, r7
 bsr    _func
 mouv.B r1, r1
 cmp    r7, r1
 scgt.L r1
 rtsd   #4, r7-r7

If the return value is zero exteneded,
"movu.B r1, r1" code can be removed.

Is the explanation san integer conversion rank?
> PS. See section 6.3.1.1 of the ISO C99 standard for more information about this
> behaviour

I think that my request is depend on rx cpu target like sh, m32r not m32c. 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45000

[Bug target/45000] RX signed extened unsigned char or short return value.

[nickc at redhat dot com]

------- Comment #3 from nickc at redhat dot com  2010-07-28 13:55 -------
Created an attachment (id=21338)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=21338&action=view)
Force functions that return small unsigned values to use zero-extension


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45000

[Bug target/45000] RX signed extened unsigned char or short return value.

[nickc at redhat dot com]

------- Comment #4 from nickc at redhat dot com  2010-07-28 14:05 -------
Hi Kazuhiro-san,

> If the func() is external function, output code is the following.
>  bsr    _func
>  mouv.B r1, r1
> If the return value is zero exteneded,
> "movu.B r1, r1" code can be removed.

Not really.  The problem is that the compiler cannot guarantee the behaviour of
the func function, since it is external to the compilation unit.  It might not
actually return an unsigned byte value.


> Is the explanation san integer conversion rank?

I am not sure what you mean here.  The simplest thing that I can say is that
the code produced by gcc is what is required by the ISO C99 standard.  If the
RX ABI requires a different behaviour then it is not compatible with the ISO
C99 standard.

That said I have uploaded a patch which offers a compromise.  It makes
functions which return small unsigned values insert a zero-extend instruction
into their epilogues.  This is less efficient than the change that you were
requesting (using MOVU.B to load the value from memory in the first place), but
it does mean that the code produced by gcc will work both with other code
produced by gcc and with code produced by Renesas's own compiler.

May I also suggest that you contact Matt Newsome <Matt.Newsome@renesas.com> at
Renesas who is also concerned with this particular problem.

Cheers
  Nick


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45000

[Bug target/45000] RX signed extened unsigned char or short return value.

[kazuhiro dot inaoka dot ud at renesas dot com]

------- Comment #5 from kazuhiro dot inaoka dot ud at renesas dot com  2010-08-03 09:32 -------
(In reply to comment #4)
Hi Nick,

My request seems to depend on Renesas callee/caller-extension spec.

> May I also suggest that you contact Matt Newsome <Matt.Newsome@renesas.com> at
> Renesas who is also concerned with this particular problem.
OK.
Please close this ticket.

Best Regards,
Kazuhiro Inaoka


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45000