Bug compiling the C version of memset with gcc -O3

[Alexander Holler]

Am 08.12.2013 03:40, schrieb Alexander Holler:
> Hello,
>
> I've stumbled over bug compiling newlib 2.0 for ARM with gcc and -O3.
>
> I'm quoting from http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59420
>
> ----
> The issue is there is a loop inside of memset that gets converted to a
> call to
> memset; that is if I read the assembly code correctly.  if that is the case
> then this is a bug in the newlib makefiles as they should be using
> -fno-tree-loop-distribute-patterns or like what glibc does:
> /* 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
>
> So closing as invalid, please report this to newlib.
>
> Note the work around is not to use -O3 or use -O3
> -fno-tree-loop-distribute-patterns .
>
> ----
>
> The bug was likely not discovered before, because most architectures
> except ARM are using optimized (assembler) versions for memset.
>
> The C comment above (likely from glibc) sounds like memmove might be too
> a victim of that optimization of gcc, but I haven't tested it up to now.

Btw., using -O3 wasn't my choice but is used by newlib as the default 
for ARM. So this bug likely affects a lot more people than just me.

Regards,

Alexander Holler