From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 1666) id 11D373858C74; Wed, 27 Jul 2022 09:24:09 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 11D373858C74 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Richard Biener To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-8624] [PR105665] ivopts: check defs of names in base for undefs X-Act-Checkin: gcc X-Git-Author: Alexandre Oliva X-Git-Refname: refs/heads/releases/gcc-12 X-Git-Oldrev: 5e45d078e36428de7c836037ec2707c538fcb774 X-Git-Newrev: 4ca164a6372412a1b3dc62b6fbde77d338e22bd4 Message-Id: <20220727092409.11D373858C74@sourceware.org> Date: Wed, 27 Jul 2022 09:24:09 +0000 (GMT) X-BeenThere: gcc-cvs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-cvs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Jul 2022 09:24:09 -0000 https://gcc.gnu.org/g:4ca164a6372412a1b3dc62b6fbde77d338e22bd4 commit r12-8624-g4ca164a6372412a1b3dc62b6fbde77d338e22bd4 Author: Alexandre Oliva Date: Fri Jun 3 03:59:03 2022 -0300 [PR105665] ivopts: check defs of names in base for undefs The patch for PR 100810 tested for undefined SSA_NAMEs appearing directly in the base expression of the potential IV candidate, but that's not enough. The testcase for PR105665 shows an undefined SSA_NAME has the same ill effect if it's referenced as an PHI_NODE arg in the referenced SSA_NAME. The variant of that test shows it can be further removed from the referenced SSA_NAME. To avoid deep recursion, precompute maybe-undefined SSA_NAMEs: start from known-undefined nonvirtual default defs, and propagate them to any PHI nodes reached by a maybe-undefined arg, as long as there aren't intervening non-PHI uses, that would imply the maybe-undefined name must be defined at that point, otherwise it would invoke undefined behavior. Also test for intervening non-PHI uses of DEFs in the base expr. The test for intervening uses implemented herein relies on dominance; this could be further extended, regarding conditional uses in every path leading to a point as an unconditional use dominating that point, but I haven't implemented that. for gcc/ChangeLog PR tree-optimization/105665 PR tree-optimization/100810 * tree-ssa-loop-ivopts.cc (ssa_name_maybe_undef_p, ssa_name_set_maybe_undef): New. (ssa_name_any_use_dominates_bb_p, mark_ssa_maybe_undefs): New. (find_ssa_undef): Check precomputed flag and intervening uses. (tree_ssa_iv_optimize): Call mark_ssa_maybe_undefs. for gcc/testsuite/ChangeLog PR tree-optimization/105665 PR tree-optimization/100810 * gcc.dg/torture/pr105665.c: New. (cherry picked from commit be2861fe8c527a5952257462ceca899bb43b1452) Diff: --- gcc/testsuite/gcc.dg/torture/pr105665.c | 20 +++++ gcc/tree-ssa-loop-ivopts.cc | 125 +++++++++++++++++++++++++++++++- 2 files changed, 141 insertions(+), 4 deletions(-) diff --git a/gcc/testsuite/gcc.dg/torture/pr105665.c b/gcc/testsuite/gcc.dg/torture/pr105665.c new file mode 100644 index 00000000000..34cfc658434 --- /dev/null +++ b/gcc/testsuite/gcc.dg/torture/pr105665.c @@ -0,0 +1,20 @@ +/* { dg-do run } */ + +int a, b, c[1], d[2], *e = c; +int main() { + int f = 0; + for (; b < 2; b++) { + int g; + if (f) + g++, b = 40; + a = d[b * b]; + for (f = 0; f < 3; f++) { + if (e) + break; + g--; + if (a) + a = g; + } + } + return 0; +} diff --git a/gcc/tree-ssa-loop-ivopts.cc b/gcc/tree-ssa-loop-ivopts.cc index 81b536f9304..549168aebd6 100644 --- a/gcc/tree-ssa-loop-ivopts.cc +++ b/gcc/tree-ssa-loop-ivopts.cc @@ -3071,13 +3071,129 @@ get_loop_invariant_expr (struct ivopts_data *data, tree inv_expr) return *slot; } -/* Find the first undefined SSA name in *TP. */ +/* Return TRUE iff VAR is marked as maybe-undefined. See + mark_ssa_maybe_undefs. */ + +static inline bool +ssa_name_maybe_undef_p (tree var) +{ + gcc_checking_assert (TREE_CODE (var) == SSA_NAME); + return TREE_VISITED (var); +} + +/* Set (or clear, depending on VALUE) VAR's maybe-undefined mark. */ + +static inline void +ssa_name_set_maybe_undef (tree var, bool value = true) +{ + gcc_checking_assert (TREE_CODE (var) == SSA_NAME); + TREE_VISITED (var) = value; +} + +/* Return TRUE iff there are any non-PHI uses of VAR that dominate the + end of BB. If we return TRUE and BB is a loop header, then VAR we + be assumed to be defined within the loop, even if it is marked as + maybe-undefined. */ + +static inline bool +ssa_name_any_use_dominates_bb_p (tree var, basic_block bb) +{ + imm_use_iterator iter; + use_operand_p use_p; + FOR_EACH_IMM_USE_FAST (use_p, iter, var) + { + if (is_a (USE_STMT (use_p)) + || is_gimple_debug (USE_STMT (use_p))) + continue; + basic_block dombb = gimple_bb (USE_STMT (use_p)); + if (dominated_by_p (CDI_DOMINATORS, bb, dombb)) + return true; + } + + return false; +} + +/* Mark as maybe_undef any SSA_NAMEs that are unsuitable as ivopts + candidates for potentially involving undefined behavior. */ + +static void +mark_ssa_maybe_undefs (void) +{ + auto_vec queue; + + /* Scan all SSA_NAMEs, marking the definitely-undefined ones as + maybe-undefined and queuing them for propagation, while clearing + the mark on others. */ + unsigned int i; + tree var; + FOR_EACH_SSA_NAME (i, var, cfun) + { + if (SSA_NAME_IS_VIRTUAL_OPERAND (var) + || !ssa_undefined_value_p (var, false)) + ssa_name_set_maybe_undef (var, false); + else + { + ssa_name_set_maybe_undef (var); + queue.safe_push (var); + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "marking _%i as maybe-undef\n", + SSA_NAME_VERSION (var)); + } + } + + /* Now propagate maybe-undefined from a DEF to any other PHI that + uses it, as long as there isn't any intervening use of DEF. */ + while (!queue.is_empty ()) + { + var = queue.pop (); + imm_use_iterator iter; + use_operand_p use_p; + FOR_EACH_IMM_USE_FAST (use_p, iter, var) + { + /* Any uses of VAR that aren't PHI args imply VAR must be + defined, otherwise undefined behavior would have been + definitely invoked. Only PHI args may hold + maybe-undefined values without invoking undefined + behavior for that reason alone. */ + if (!is_a (USE_STMT (use_p))) + continue; + gphi *phi = as_a (USE_STMT (use_p)); + + tree def = gimple_phi_result (phi); + if (ssa_name_maybe_undef_p (def)) + continue; + + /* Look for any uses of the maybe-unused SSA_NAME that + dominates the block that reaches the incoming block + corresponding to the PHI arg in which it is mentioned. + That means we can assume the SSA_NAME is defined in that + path, so we only mark a PHI result as maybe-undef if we + find an unused reaching SSA_NAME. */ + int idx = phi_arg_index_from_use (use_p); + basic_block bb = gimple_phi_arg_edge (phi, idx)->src; + if (ssa_name_any_use_dominates_bb_p (var, bb)) + continue; + + ssa_name_set_maybe_undef (def); + queue.safe_push (def); + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "marking _%i as maybe-undef because of _%i\n", + SSA_NAME_VERSION (def), SSA_NAME_VERSION (var)); + } + } +} + +/* Return *TP if it is an SSA_NAME marked with TREE_VISITED, i.e., as + unsuitable as ivopts candidates for potentially involving undefined + behavior. */ static tree -find_ssa_undef (tree *tp, int *walk_subtrees, void *) +find_ssa_undef (tree *tp, int *walk_subtrees, void *bb_) { + basic_block bb = (basic_block) bb_; if (TREE_CODE (*tp) == SSA_NAME - && ssa_undefined_value_p (*tp, false)) + && ssa_name_maybe_undef_p (*tp) + && !ssa_name_any_use_dominates_bb_p (*tp, bb)) return *tp; if (!EXPR_P (*tp)) *walk_subtrees = 0; @@ -3114,7 +3230,7 @@ add_candidate_1 (struct ivopts_data *data, tree base, tree step, bool important, /* If BASE contains undefined SSA names make sure we only record the original IV. */ bool involves_undefs = false; - if (walk_tree (&base, find_ssa_undef, NULL, NULL)) + if (walk_tree (&base, find_ssa_undef, data->current_loop->header, NULL)) { if (pos != IP_ORIGINAL) return NULL; @@ -8192,6 +8308,7 @@ tree_ssa_iv_optimize (void) auto_bitmap toremove; tree_ssa_iv_optimize_init (&data); + mark_ssa_maybe_undefs (); /* Optimize the loops starting with the innermost ones. */ for (auto loop : loops_list (cfun, LI_FROM_INNERMOST))