https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102943
--- Comment #37 from Richard Biener <rguenth at gcc dot gnu.org> --- I'm looking at range_def_chain::m_def_chain, it's use is well obfuscated by inheritance but comments suggest that we have one such structure either for each edge in the CFG or for each basic-block. In particular this m_def_chain vector looks very sparse and fat, replacing that with a hash_map<int, rdc *> and allocating rdcs from another obstack (in principle re-using m_bitmap.obstack would be possible but somewhat ugly) should make this more cache and memory friendly (whether SSA name version or pointer is used as key would remain to be determined). The ssa1 and ssa2 members are also quite odd, we always record into the bitmap so those seem to be a waste of time? Changing allocation the above way would also enable embedding bitmap_head, removing one pointer indirection. Unfortunately we use bitmap_ior_into so using the more efficient tree form for bitmap queries isn't possible until somebody implements (efficient!) bitmap_ior_into on tree form. It wouldnt't fix the appearant algorithmic issues of course, so just food for thought. Complexity wise it would reduce O (n-edges * n-ssa-names) to O (n-edges * n-deps/imports-on-edge).
