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Re: Deprecating cc0 (and consequently cc0 targets)



> On Sep 20, 2019, at 1:45 PM, Jeff Law <law@redhat.com> wrote:
> 
> On 9/20/19 11:22 AM, Richard Biener wrote:
>> ...
>> It seems to be that for the goal to keep a target alive a variant #2
>> conversion (according to the wiki) should be closely mirror CC0
>> behavior and thus should be easier to achieve and with less patterns
>> touched than the 'good' variant. Can you acknowledge that and would
>> such 'simple' conversions be OK?
> Unless the target has condition code preserving arithmetic a variant #2
> conversion is the only way to go.

Yes.

> Now if someone did a variant #2 without the optimization bits (ie,
> adding appropriate _set_flags pattern variants), I think that should be
> considered explicitly OK even though the code quality would potentially
> suffer.  Essentially it's a choice between dropping the port or keeping
> the port, but with slightly less optimization.  THe latter seems like a
> better choice to me.

True.  Then again, the added work of creating the pattern pairs is modest.  With define_subst, much of the work can be automated.

For pdp11, I found this to be the case; the hard part was to learn what is needed, and for that the Wiki ends up a big help.  Also, pdp11 is harder than most because it has two CC registers (one for float ops, one for the rest).  I don't know all the others, but for example VAX only has one, and I'm pretty sure the same applies to m68k.

	paul



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