https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83565
Jeffrey A. Law <law at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |law at redhat dot com
--- Comment #27 from Jeffrey A. Law <law at redhat dot com> ---
WORD_REGISTER_OPERATIONS says the operations in integral modes smaller than a
word are performed on the entire register (ie a word).
I think WORD_REGISTER_OPERATIONS is fairly intuitive when it comes to
arithmetic and logicals. For arith/logicals I would find myself agreeing with
Eric in c#25.
However, I think it's not as clear for shifts/rotates.
On the PA (which defines WORD_REGISTER_OPERATIONS) we have 32bit
deposit/extract which are used for various shifts. The 32bit extract/deposit
instructions set the low 32 bits in the expected way, but leave the upper bits
undefined. So I suspect PA and IA-64 have similar behavior (big surprise).
One could argue that WORD_REGISTER_OPERATIONS should apply to just arith and
logicals. One could also argue that it should apply to shifts in which case
ports like the PA and IA-64 probably shouldn't define WORD_REGISTER_OPERATIONS.
If we were to argue that WORD_REGISTER_OPERATIONS should apply to just
arith/logicals, then the PA would need to be audited for cases where we might
implement an arith operation using shifts (deposit/extract instructions).
And just to be clear here. I don't think the PA or IA-64 ought to drive
decisions in this area. They're both dead architectures -- but others may have
similar properties.
Note none of this touches on what are the high bits of a paradoxical subreg,
which are undefined in RTL. So I'm in partial agreement with Jim c#11 as well.
