[Bug target/43892] PowerPC suboptimal "add with carry" optimization
joakim.tjernlund at transmode dot se
gcc-bugzilla@gcc.gnu.org
Mon Jan 19 00:05:00 GMT 2015
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43892
--- Comment #24 from joakim.tjernlund at transmode dot se <joakim.tjernlund at transmode dot se> ---
(In reply to Segher Boessenkool from comment #23)
> Do you know what addcc does? PowerPC does not have any instruction
No, just guessing :) To me it was generic way to express add with carry
> that behaves like it at all. So it would have to expand to a big
> fat sequence of instructions, that then hopefully are optimised to
> something sane later. Instead, the current code expands to something
> sane immediately.
I was hoping that this
add 3,3,4
subfc 0,4,3
subfe 0,0,0
subfc 0,0,3
mr 3,0
could be this instead, once you had notion for carry in gcc for ppc:
addc 3,3,4
addze 3,3
the optimized loop would be an extra bonus
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