diff options
Diffstat (limited to 'gcc/tree-ssa-loop-ivopts.cc')
-rw-r--r-- | gcc/tree-ssa-loop-ivopts.cc | 125 |
1 files changed, 121 insertions, 4 deletions
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 <gphi *> (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<tree> 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 <gphi *> (USE_STMT (use_p))) + continue; + gphi *phi = as_a <gphi *> (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)) |