http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37916
--- Comment #20 from Hans-Peter Nilsson <hp at gcc dot gnu.org> 2011-03-11 01:31:14 UTC --- (In reply to comment #19) > Random thought on this PR: With a scheduler description, -fschedule-insns > -fsched-pressure may help. That theory should be testable by compiling for e.g. a x86_64 target; see comment #12, but to answer your question... > Is there a reason why there is no scheduler description? Yes. For a while, there was nothing to schedule. ...except for CPUs in systems a cache, where it helps to schedule to avoid RaW hazards. ...and then pipelined variants came, with other hazards to schedule (to avoid bubbles, no mips1-type madness). ...but then, I noticed that scheduling with the "new" scheduler wasn't supported for CC0 targets. ...which later was either fixed, or just a plain misunderstanding (cf. m68k/cf.md). ...and when checking the cycle-correct simulator, I found that there weren't many cycles to schedule away, hence a fair amount of work for no apparent gain, at least for the intended purpose of insn scheduling. There you go, the reasons in a nutshell. And while there's still a possibility that it's a pragmatic solution (modulo #c12), it doesn't strike me as requiring a scheduler to be the Right Thing to do for a fix to this problem. (Though from a general GCC maintenance perspective, automatically defaulting to a trivial scheduler might be a good idea.)
