------- Additional Comments From bjoern dot m dot haase at web dot de 2005-09-06 12:59 ------- I have done some code reading now and come to the following conclusion: When having an expanded sequence that provides one single result, libcall blocks are an appropriate method for making sure that a single-set insn that carries a REG_EQUAL note is *not* deleted too early. Libcall notes, however, do not provide a method so far for dealing with library calls or expanded sequences that yield *two* results. E.g. they are no solution for both, divmod4 on the one hand and arithmetic expanders doing subreg lowering and also yielding a CC on the other hand. In order to keep changes as small as possible, my suggestion is to change static void rest_of_handle_jump2 (void) such that it no longer calls "delete_trivially_dead_insns ()" at it's very beginning. (I'd have posted a patch, if savannah.gnu.org is down right now.) IIUC that the trivially dead insn are in first line a performance issue because they need memory and handling that would otherwise not be necessary, my suggested change would not be too serious. "delete_trivially_dead_insns ()" would be among the first things that is called in the pass that immediately follows jump2: The first cse pass. I'd appreciate comments on whether such trivially dead insn could prevent jump2 from realizing important optimization steps. Bjoern.
-- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23726
