> About the 1st question. Before gcc4.7, the only class (allocno class) > used for coloring can be a cover class. So it was not possible to use > GENERAL_OR_EXTRA_FP_REGS in gcc4.6 and older versions. Starting gcc4.7, > class used for coloring can be any class which is more profitable than > memory. Although there is inaccuracy in cost calculations for -O1 > because only one pass for cost calculations is used (it is very > expensive pass). To get better cost evaluations, more passes should be > used. But again we don't do more 2 passes because even one pass is not > cheap. > > In brief, I don't see any criminal that the class calculation is > different for -O1 and -O2.
Fine with me. I'm going to apply the above patchlet then. > About the 2nd question. It seems to me wrong. I'd remove function > process_bb_node_for_hard_reg_moves and its call from > setup_allocno_cover_class_and_costs because function > process_regs_for_copy is more accurate (it works with subreg). > Although, I might be miss something here. There were a lot of problems > and tunings of cost calculation code. Generated code *performance* (and > even generation of *valid* code) is very sensitive to changes in > ira-costs.c. So even if such change looks obvious, a lot of testing and > benchmarking should be done. I could do that but it will take a week or > two before committing such change if everything is ok. Understood. I essentially wanted to bring this to your attention, since it looked like a small oddity to me. This might be something to play with for future improvements, but it's your call of course. Thanks for the detailed answer. -- Eric Botcazou
