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Re: PATCH: PR target/40470: unable to find a registe r to spill in class ‘SSE_FIRST_REG’


On 6/18/09, Ian Lance Taylor <iant@google.com> wrote:
> Vladimir Makarov <vmakarov@redhat.com> writes:
>
> > I looked at this problem.  It looks like
> >
> > xmm0=call
> > p666= xmm0
> > ...
> > insn in the question (spill failure because it needs xmm0)
> > ...
> > = p666, dead p666
> >
> > The combiner removes p666=xmm0 and uses xmm0 instead of p666 in the
> > last insn.
>
> That sounds like a bad idea, particularly if SMALL_REGISTER_CLASSES or
> FUNCTION_VALUE_REGNO_P (regno).

Iff my hookizazion patch for SMALL_REGISTER_CLASSES would be approved,
the problem would get worse.

The problem here is that combine apparently does copy propagation of
hard registers. That is a transformation we avoid like the plague
everywhere else AFAIC (at least cse and cprop have guards against this
or just do not handle hard regs at all).

So my proposed solution would be: Do not allow combine to propagate
SETany _SRC that contains hard regs.

Ciao!
Steven


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