On Tue, Oct 23, 2012 at 7:36 AM, Zhenqiang Chen <zhenqiang.c...@linaro.org> wrote: > Hi, > > PRE bases on the result of value numbering (run_scc_vn). At the end, > it free_scc_vn. But before free_scc_vn, it might call cleanup_tree_cfg > (); > > if (do_eh_cleanup || do_ab_cleanup) > cleanup_tree_cfg (); > > cleanup_tree_cfg might call make_ssa_name which might reuse some > "name" from the FREE_SSANAMES list. If the VN_INFO of the "name" is > NULL, free_scc_vn will "Segmentation fault". PR 54902 > (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54902) shows a real case. > The attached log shows the gdb backtrace to create a new ssa name. > > Here is function VN_INFO: > > vn_ssa_aux_t > VN_INFO (tree name) > { > vn_ssa_aux_t res = VEC_index (vn_ssa_aux_t, vn_ssa_aux_table, > SSA_NAME_VERSION (name)); > gcc_checking_assert (res); > return res; > } > > Can we make sure "res" is not NULL for the new ssa name? > > In trunk, Richard's "Make gsi_remove return whether EH cleanup is > required" patches in r186159 and r186164 make "do_eh_cleanup" to > false. So cleanup_tree_cfg is not called in PRE. Then no new ssa name > will be created. > > Does the Richard's patch fix the root cause?
I don't think so. Where does cfgcleanup call make_ssa_name? The solution would be to post-pone cleaning up the CFG until after free_ssc_vn. To be able to compute dominators we only have to remove unreachable blocks (delete_unreachable_blocks) Richard. > Thanks! > -Zhenqiang
