On Wed, Oct 24, 2012 at 3:13 AM, Zhenqiang Chen <zhenqiang.c...@linaro.org> wrote: > On 23 October 2012 18:02, Richard Biener <richard.guent...@gmail.com> wrote: >> 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) > > The attachment (bt.log) in previous mail shows the trace to call > make_ssa_name. PR 54902 includes a test case to reproduce it. The > bt.log bases on 4.7. > > I have no case to reproduce it for trunk. But cleanup_tree_cfg is > still called before free_ssc_vn.
Ah, call folding on block merging ... :/ I suppose we can even end up leaking memory that way when SSA names are released there. Let me take the bug. Richard. > Thanks! > -Zhenqiang
