------- Additional Comments From wilson at gcc dot gnu dot org 2005-01-05
03:44 -------
This question was asked and mostly answered on the gcc mailing list.
http://gcc.gnu.org/ml/gcc/2004-12/msg00231.html
http://gcc.gnu.org/ml/gcc/2004-12/msg00234.html
As per the ABI, small local data ("own" data) is placed in the small data
section in the GOT, where it can be accessed with a single memory reference. If
we put it in the read-only data section, it would require two memory references
to access it, resulting in slower code.
Since the C testcase is invalid, this is not a good enough reason to disable an
optimization by default.
However, as Richard Henderson mentioned, we could optionally put the variable in
a read-only data section if the user requested it via an option, or if the
Fortran standard requires it. I don't know if the Fortran standard requires
this, I doubt that it does.
Incidentally, this issue is not unique to the IA-64 port. There are other
targets that behave the same way, mips-elf for instance. So you may still have
this problem when porting code to other systems even if the IA-64 port was
fixed.
There is an option that will make your testcase work as you expect, the
-mno-sdata option. This is overkill for your purposes though, as this prevents
any variable from going in sdata, whereas you only want to prevent putting const
variables in sdata.
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What |Removed |Added
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CC| |wilson at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18566
