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Re: Bug compiling the C version of memset with gcc -O3

Am 08.12.2013 03:40, schrieb Alexander Holler:

I've stumbled over bug compiling newlib 2.0 for ARM with gcc and -O3.

I'm quoting from

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.  */
# define inhibit_loop_to_libcall \
     __attribute__ ((__optimize__ ("-fno-tree-loop-distribute-patterns")))
# define inhibit_loop_to_libcall

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.


Alexander Holler

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