Gcc has traditionally used the concept of a compare operation that stores
a comparison result in CC0 or a register, and then can be used with arbitrary
comparison operators to compare it against zero to make a decision for
a branch, store flag, or conditional move instruction.
Since often the actual comparison instructions work differently, a number of
ports need to stash away the comparison operands when they pretend to emit
a comparison, and then emit the actual comparison later when its result is
cbranch* / cstore* patterns had the promise to get rid of this bogosity,
however, they are still don;t deliver.
The only way to have a conditional move is to first perform a comparison, and
then have the the actual move depende on the comparison result. Thus, if
the architecture has conditional move, a comparison patterns are needed, even
if the targets compare operations are ill-matched, compare patterns have to be
defined, thus disabling cbranch* / cstore* patterns.