Matt Turner <[email protected]> writes: > CSE would otherwise combine the two mul(8) emitted by [iu]mulExtended: > > mul(8) acc0 x y > mach(8) null x y > mov(8) lsb acc0 > ... > mul(8) acc0 x y > mach(8) msb x y > Into: > mul(8) temp x y > mov(8) acc0 temp > mach(8) null x y > mov(8) lsb acc0 > ... > mov(8) acc0 temp > mach(8) msb x y > > But mul(8) into the accumulator produces more than 32-bits of precision, > which is required and lost if multiplying into a general register and > moving to the accumulator.
I tried to come up with a case that we wanted CSE on a general register description instead of our abstract files, and couldn't come up with any. These two (2/4, 3/4) are: Reviewed-by: Eric Anholt <[email protected]>
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