[Bug rtl-optimization/44281] [4.3/4.4/4.5/4.6 Regression] Global Register variable pessimisation

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44281

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-04 11:22:51 UTC ---
You are talking about this single testcase, I'm talking in general that if gcc
is on x86_64 tuned for a medium sized general purpose register file and you
suddenly turn it into a very limited size general purpose register file, you
can get non-optimal code.  Such bugreports are definitely much lower priority
than what you get with the common case where no global register vars are used,
or at most one or two.  The "weird" saving/restoring of %rdi into/from %r10 is
because the RA chose to use %rdi for a temporary used in incrementing of REG7
and loading the next pointer from it, while postreload managed to remove all
needs for such a temporary register, it is too late for the save/restore code
not to be emitted.