[Bug debug/48866] gcc hangs when -g is set

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48866

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-05-04 14:21:28 UTC ---
The problem is the MEMs nested in other MEM addresses, cselib isn't prepared to
handle it efficiently.

So, either we should break very deep MEM nests using extra DEBUG_INSNs and
debug temporaries (not sure how easy it would be to break them during
expand_debug_expr, so perhaps either when expand_debug_expr finishes, or
perhaps during vt_initialize before an insn is passed to cselib_process_insn),
or cselib would need to have some cache on MEMs it already looked up during
current toplevel cselib_lookup or cselib_subst_to_values calls - for small
number of MEMs perhaps a linear cache that cselib_lookup_mem could iterate
over, holding
MEM rtx / corresponding cselib_val * pairs, for bigger amounts perhaps
pointer_map.  Without such a cache, 14 nested MEMs result in certainly more
than
4 billion cselib_lookup searches within one cselib_process_insn.