[Bug target/18566] Can vary constants (undefined fortran)

["wilson at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- 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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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18566