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Re: [Patch,AVR]: Fix PR50447 (2/n)
On 09/23/2011 10:56 AM, Paolo Bonzini wrote:
Also, I am curious about one thing: while this is of course a very
pragmatic solution, you could also convert AVR to get rid of CC0, do
this at expansion time, and get split-wide-types to work as intended.
compare-elim.c makes it relatively easy to remove CC0 nowadays.
For example, a two-byte add can be written as
(set (reg:QI L1) (plus:QI (reg:QI L2) (reg:QI L3)))
(set (reg:QI H1) (plus:QI
(plus:QI (req:QI H2) (reg:QI H3))
(ltu:QI (reg:QI L1) (reg:QI L3))))
After reload the second instruction can be split to
(set (reg:CC_C CC) (compare:QI (reg:QI L1) (reg:QI L3)))
(set (reg:QI H1) (plus:QI
(plus:QI (req:QI H2) (reg:QI H3))
(lt:QI (reg:CC_C CC) (const_int 0))))
(i.e. cp+adc). compare-elim will then be able to turn this into add+adc:
[parallel
(set (reg:QI L1) (plus:QI (reg:QI L2) (reg:QI L3)))
(set (reg:CC_C CC) (compare:QI
(plus:QI (reg:QI L2) (reg:QI L3))
(reg:QI L3))))]
(set (reg:QI H1) (plus:QI
(plus:QI (req:QI H2) (reg:QI H3))
(lt:QI (reg:CC_C CC) (const_int 0))))
Paolo