> This optimizes byte_from_pos and pos_from_bit by noting that we operate > on sizes whose computations have no intermediate (or final) overflow. > This is the single patch necessary to get Ada to bootstrap and test > with TYPE_IS_SIZETYPE removed. Rather than amending size_binop > (my original plan) I chose to optimize the above two commonly used > accessors. > > Conveniently normalize_offset can be re-written to use pos_from_bit > instead of inlinig it. I also took the liberty to document the > functions (sic).
Nice, thanks. Could you add a blurb, in the head comment of the first function in which you operate under the no-overflow assumption, stating this fact and why this is necessary (an explicit mention of Ada isn't forbidden ;-), as well as a cross-reference to it in the head comment of the other function(s). > Any comments? Would you like different factoring of the optimization > (I considered adding a byte_from_bitpos)? Any idea why > byte_from_pos is using TRUNC_DIV_EXPR (only positive offsets?) and > pos_from_bit FLOOR_DIV_EXPR (also negative offsets?) - that seems > inconsistent, and we fold FLOOR_DIV_EXPR of unsigned types (sizetype) > to TRUNC_DIV_EXPR anyways. I think that a bit position is treated as non-negative, so bitpos can use TRUNC_DIV_EXPR in byte_from_pos and you need to use FLOOR_MOD_EXPR to get a non-negative *pbitpos in pos_from_bit. Very likely obsolete now indeed. -- Eric Botcazou
