This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [RFA] [PATCH][PR tree-optimization/59749] Fix recently introduced ree bug
- From: Jeff Law <law at redhat dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 10 Jan 2014 15:53:12 -0700
- Subject: Re: [RFA] [PATCH][PR tree-optimization/59749] Fix recently introduced ree bug
- Authentication-results: sourceware.org; auth=none
- References: <52D067EF dot 7020005 at redhat dot com> <20140110215227 dot GJ892 at tucnak dot redhat dot com>
On 01/10/14 14:52, Jakub Jelinek wrote:
There is one thing I still worry about, if some target has
an insn to say sign extend or zero extend a short memory load
into HARD_REGNO_NREGS () > 1 register, but the other involved
register has the only one (or fewer) hard registers available to it.
Consider registers SImode hard registers 0, 1, 2, 3:
(set (reg:SI 3) (something:SI))
(set (reg:HI 0) (expression:HI))
(set (reg:SI 2) (sign_extend:SI (reg:HI 0)))
(set (reg:DI 0) (sign_extend:DI (reg:HI 0)))
(use (reg:SI 3))
we transform this into:
(set (reg:SI 3) (something:SI))
(set (reg:SI 2) (sign_extend:SI (expression:HI)))
(set (reg:SI 0) (reg:HI 2))
(set (reg:DI 0) (sign_extend:DI (reg:HI 0)))
(use (reg:SI 3))
first (well, the middle is then pending in copy list), and next:
(set (reg:SI 3) (something))
(set (reg:DI 2) (sign_extend:DI (expression:HI)))
(set (reg:DI 0) (reg:DI 2))
(use (reg:SI 3))
but that looks wrong, because the second instruction would now clobber
(reg:SI 3). Dunno if we have such an target and thus if it is possible
to construct a testcase.
Seems like any port where we can do operations on 3 different modes and
the largest mode requires > 1 hard reg ought to do. I don't see
anything inherent in this setup that wouldn't apply to x86 for example.
So, I'd say the handling of the second extend should notice that
it is actually extending load into a different register and bail out
if it would need more hard registers than it needed previously, or
something similar.
That ought to be a trivial check to add. Let me add it and see if I
can find something to trip it.
The printf prototype isn't needed, and the noreturn attributes
aren't needed either, as they are builtins, the compiler will
add those automatically.
The printf prototype came from the original and I forgot to remove it
when I zapped the printf statement. As for abort/exit, they're not
strictly needed, but they shut up the compiler when running things by
hand during testing/development. They're easy enough to zap.
Thanks,
Jeff