------- Comment #36 from lucier at math dot purdue dot edu 2008-09-04 20:39 ------- I don't really understand the status of this bug.
Before 4.3.0, it was P!, and Mark said he said he'd "like to see us start to explain these kinds of dramatic performance changes." There was quite a bit of detective work that ended with "for some reason gcc-4.3 transforms only _some_ instructions (line 708+ in _.085t.fre dump) ...". Richard opined that it was an "alias partitioning problem", but Uros noted that for the original code instead of the reduced testcase expanding some parameter to its maximum still doesn't fix the problem. So (a) we don't know what the current code is doing wrong, and (b) we don't know why 4.2 got it right. So I don't think Mark got what he wanted, and now it's P2, and each release the target release for fixing it gets pushed back. I've been testing mainline on this bug sporadically, especially when an entry in gcc-patches mentions some words that also appear on this PR, to see if it's fixed. I'm a bit concerned that the target of 4.3.* is becoming increasingly out of reach, as changes committed to that branch seem to be more and more conservative because it's a release branch. I don't think the code for this bug is terribly atypical for machine-generated code; it would be nice to be able to remove this performance regression. Unfortunately, I'm in no position to do so. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33928
