On Tue, Nov 23, 2010 at 9:09 PM, Joern Rennecke <amyl...@spamcop.net> wrote: > If we changed BITS_PER_UNIT into an ordinary piece-of-data 'hook', this > would not only cost a data load from the target vector, but would also > inhibit optimizations that replace division / modulo / multiply with shift > or mask operations. > So maybe we should look into having a few functional hooks that do common > operations, i.e. > bits_in_units x / BITS_PER_UNIT > bits_in_units_ceil (x + BITS_PER_UNIT - 1) / BITS_PER_UNIT > bit_unit_remainder x % BITS_PER_UNIT > units_in_bits x * BITS_PER_UNIT > > Although we currently have some HOST_WIDE_INT uses, I hope using > unsigned HOST_WIDE_INT as the argument / return type will generally work. > > tree.h also defines BITS_PER_UNIT_LOG, which (or its hook equivalent) > should probably be used in all the places that use > exact_log_2 (BITS_PER_UNIT), and, if it could be relied upon to exist, we > could also use it as a substitute for the above hooks. However, this seems > a bit iffy - we'd permanently forgo the possibility to have 6 / 7 / 36 > bit etc. units. > > Similar arrangements could be made for BITS_PER_WORD and UNITS_PER_WORD, > although these macros seem not quite so prevalent in the tree optimizers.
Well. Some things really ought to stay as macros. You can always error out if a multi-target compiler would have conflicts there at configure time. Richard.
