http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56439
Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |gjl at gcc dot gnu.org
--- Comment #8 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2013-03-07
23:26:01 UTC ---
(In reply to comment #3)
> (In reply to comment #2)
>> Any specific sections you can point me to? I'd be interested to hear a
>> justification for this behavior.
>
> Simple answer, an interrupt can happen any time after the access/assignment of
> the global register variable so it needs to be set to the value and treated as
> a volatile variable.
Is this really the case? There is not even a means to tag a REG as volatile.
The /v flag is set but for REGs it means "user variable", see rtl.h and the
docs for volatil.
http://gcc.gnu.org/viewcvs/trunk/gcc/rtl.h?view=markup#l286
And qualifying foo as volatile diagnoses as expected:
<stdin>:1:1: warning: optimization may eliminate reads and/or writes to
register variables [-Wvolatile-register-var]
This issue looks rather like a fallout of reload that for some reasons spills
for the shift insn.
See also PR49491
Or are global registers spacial for reload? I still don't see why a spilling is
needed for the shift insn...
