https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84178
--- Comment #6 from David Malcolm <dmalcolm at gcc dot gnu.org> --- Author: dmalcolm Date: Thu Mar 8 12:17:36 2018 New Revision: 258363 URL: https://gcc.gnu.org/viewcvs?rev=258363&root=gcc&view=rev Log: tree-if-conv.c: fix ICE seen with -fno-tree-forwprop (PR tree-optimization/84178) PR tree-optimization/84178 reports a couple of source files that ICE inside ifcvt when compiled with -03 -fno-tree-forwprop (trunk and gcc 7). Both cases involve problems with ifcvt's per-BB gimplified predicates. Testcase 1 fails this assertion within release_bb_predicate during cleanup: 283 if (flag_checking) 284 for (gimple_stmt_iterator i = gsi_start (stmts); 285 !gsi_end_p (i); gsi_next (&i)) 286 gcc_assert (! gimple_use_ops (gsi_stmt (i))); The testcase contains a division in the loop, which leads to if_convertible_loop_p returning false (due to gimple_could_trap_p being true for the division). This happens *after* the per-BB gimplified predicates have been created in predicate_bbs (loop). Hence tree_if_conversion bails out to "cleanup", but the gimplified predicates exist and make use of SSA names; for example this conjunction for two BB conditions: _4 = h4.1_112 != 0; _175 = (signed char) _117; _176 = _175 >= 0; _174 = _4 & _176; is using SSA names. This assertion was added in r236498 (aka c3deca2519d97c55876869c57cf11ae1e5c6cf8b): 2016-05-20 Richard Biener <rguent...@suse.de> * tree-if-conv.c (add_bb_predicate_gimplified_stmts): Use gimple_seq_add_seq_without_update. (release_bb_predicate): Assert we have no operands to free. (if_convertible_loop_p_1): Calculate post dominators later. Do not free BB predicates here. (combine_blocks): Do not recompute BB predicates. (version_loop_for_if_conversion): Save BB predicates around loop versioning. * gcc.dg/tree-ssa/ifc-cd.c: Adjust. The following patch fixes this by adding a call to gimple_seq_discard to release_bb_predicate. It also updates the assertion, so that instead of asserting the stmts have no imm uses, instead assert that they weren't added to a bb before discarding them (otherwise discarding them would be a bug). We know this is the case because insert_gimplified_predicates has: /* Once the sequence is code generated, set it to NULL. */ set_bb_predicate_gimplified_stmts (bb, NULL); but asserting it seems appropriate as a double-check. The patch doesn't address the 2nd issue within PR tree-optimization/84178. gcc/ChangeLog: PR tree-optimization/84178 * tree-if-conv.c (release_bb_predicate): Remove the the assertion that the stmts have NULL use_ops. Discard the statements, asserting that they haven't yet been added to a BB. gcc/testsuite/ChangeLog: PR tree-optimization/84178 * gcc.c-torture/compile/pr84178-1.c: New test. Added: trunk/gcc/testsuite/gcc.c-torture/compile/pr84178-1.c Modified: trunk/gcc/ChangeLog trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-if-conv.c
