[Bug tree-optimization/46590] [4.6/4.7/4.8 Regression] long compile time with -O2 and many loops

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46590

--- Comment #35 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-04 13:17:53 UTC ---
With -O1 FRE uses loads of memory and compile-time.  Not the value-numbering
itself but compute_avail ()!  Bah.  Of course AVAIL sets get bigger and
bigger going down the dominator tree.  For FRE a single domwalk after
SCCVN computing "avail" and doing elimiation would be enough.  Especially
as all the overhead in AVAIL is just SSA DEFs and their value.