[Bug target/92140] clang vs gcc optimizing with adc/sbb
segher at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Fri Oct 18 15:54:00 GMT 2019
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92140
--- Comment #20 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Ah, okay. So it is either one or two insns (zero can not be handled, but you
can do a noop, a move of a reg to itself, and that will be optimised away just
fine). Three insns is not something combine ever handles at all: it's always
{2,3,4}->{1,2}.
Since some years new pseudos *can* be created during combine, but there are
various problems with that still.
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