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Re: [PATCH 04/25] SPECIAL_REGNO_P
> On Sep 13, 2018, at 10:08 AM, Andrew Stubbs <ams@codesourcery.com> wrote:
>
> On 13/09/18 11:01, Andrew Stubbs wrote:
>> The assert is caused because the def-use chains indicate that SCC conflicts with itself. I suppose the question is why is it doing that, but it's probably do do with that being a special register that gets used in split2 (particularly by the addptrdi3 pattern). Although, those patterns are careful to save SCC to one side and then restore it again after, so I'd have thought the DF analysis would work out?
>
> I think I may have a theory on this one now....
>
> The addptrdi3 pattern must use two 32-bit adds with a carry in SCC, but addptr patterns are not allowed to clobber SCC, so the splitter carefully saves and restores the old value.
If you don't have machine operations that add without messing with condition codes, wouldn't it make sense to omit the definition of the add-pointer patterns? GCC will build things out of normal (CC-clobbering) adds if there are no add-pointer operations, which may well be more efficient in most cases than explicitly saving/restoring a CC that may in fact not matter right at that spot.
paul