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Re: Recursive calloc() due to optimization




On 25/03/15 14:01, Marc Glisse wrote:
On Wed, 25 Mar 2015, Sebastian Huber wrote:

Hello,

I updated to GCC 5 and now it turns the RTEMS calloc() implementation into

Disassembly of section .text:

00000000 <calloc>:
  0:   fb01 f000       mul.w   r0, r1, r0
  4:   2101            movs    r1, #1
  6:   f7ff bffe       b.w     0 <calloc>
  a:   bf00            nop

on ARM. How can I disable this optimization? I tried

__attribute__((__optimize__("-fno-builtin")))
void *calloc(
 size_t nelem,
 size_t elsize
)
{
 char   *cptr;
 size_t  length;

 length = nelem * elsize;
 cptr = malloc( length );
 if ( cptr )
   memset( cptr, '\0', length );

 return cptr;
}

but this doesn't work. It this one of the -fno-tree-* options?

-fno-builtin is good, but you cannot use it in an optimize attribute.

This is quite confusing since for other optimiziations in this area it works like that, e.g. glibc (include/libc-symbols.h):

/* Add the compiler optimization to inhibit loop transformation to library
   calls.  This is used to avoid recursive calls in memset and memmove
   default implementations.  */
#ifdef HAVE_CC_INHIBIT_LOOP_TO_LIBCALL
# define inhibit_loop_to_libcall \
    __attribute__ ((__optimize__ ("-fno-tree-loop-distribute-patterns")))
#else
# define inhibit_loop_to_libcall
#endif

--
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber@embedded-brains.de
PGP     : Public key available on request.

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