On 18/04/12 11:55, Richard Sandiford wrote:
The problem is that not all register moves are always going to be
eliminated, even when no mode changes are involved. It might make
sense to restrict that code you quoted:
if (MODES_TIEABLE_P (GET_MODE (x), word_mode))
bitmap_set_bit (decomposable_context, regno);
to the second pass though.
Yes, I thought of that, but I dismissed it because the second pass is
really very late. It would be just in time to take advantage of the
relaxed register allocation, but would miss out on all the various
optimizations that forward-propagation, combining, and such can offer.
This is why I've tried to find a way to do something about it in the
first pass. I thought it makes sense to do something for none-no-op
moves (when is there such a thing, btw, without it being and extend,
truncate, or subreg?),