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Re: PATCH: Darwin specific 1-liners (1)
- From: David Edelsohn <dje at watson dot ibm dot com>
- To: Richard Henderson <rth at redhat dot com>, Daniel Berlin <dan at cgsoftware dot com>, Stan Shebs <shebs at apple dot com>, dalej at apple dot com, gcc-patches at gcc dot gnu dot org
- Date: Thu, 06 Dec 2001 13:31:35 -0500
- Subject: Re: PATCH: Darwin specific 1-liners (1)
>>>>> Richard Henderson writes:
Richard> This isn't the way preference works anymore. The problem is with ports
Richard> that have different mnemonics -- particularly for move insns -- and so
Richard> really have to use different alternatives. So now we look over the set
Richard> of alternatives and see if there's a superclass that contains them, and
Richard> if so, use that as a preference.
Richard> I recommend "c,*l", since that will cause CTR to be preferred in the
Richard> register allocator, but reload will happily use LR if the value
Richard> happens to already be there.
I was trying to use LR -- even when the value was not already
there -- if GCC decided that CTR was "too expensive". That's the
fundamental performance question that Dale hopefully can comment on: Do we
*ALWAYS* want to use CTR unless the value happens to be in LR *OR* do we
(strongly?) discourage use of LR.
David