------- Comment #5 from rguenther at suse dot de 2008-04-19 01:50 ------- Subject: Re: [4.4 Regression] load-PRE missed opportunities without SFTs
On Fri, 18 Apr 2008, aldot at gcc dot gnu dot org wrote: > ------- Comment #4 from aldot at gcc dot gnu dot org 2008-04-18 18:00 ------- > While not really useful, i dare to state that SCC(N)-VN unfortunately misses a > lot of what it is ment to serve (IMHO), generally: > > 1) PR11832 > testcase from http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11832#c0 > Needs adjustment (looked into it -- AFAICR -- befor 4.3 was branched; didn't > retry after you recently touching SCCVN, i admit) > > 2) PR5738 > The testcase from http://gcc.gnu.org/bugzilla/show_bug.cgi?id=5738#c0 > is completely undiagnosed (and _severely_ mishandled -- IMHO) by current > SCCVN. > This one is particularly mean since you may run into dominator related > pitfalls > very, very fast, from what i've seen (before you touched tree-ssa-pre, > admitteldy). > > A couple of sensible and nice improvements are mentioned in ยน) above. These are both testcases for missed code-motion which neither PRE nor FRE performs. While SCCVN can figure out that two stmts compute the same value it still needs a pass that makes use of it ;) Richard. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35972
