/* SSA Dominator optimizations for trees Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc. Contributed by Diego Novillo This file is part of GCC. GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GCC; see the file COPYING. If not, write to the Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "tree.h" #include "flags.h" #include "rtl.h" #include "tm_p.h" #include "ggc.h" #include "basic-block.h" #include "cfgloop.h" #include "output.h" #include "expr.h" #include "function.h" #include "diagnostic.h" #include "timevar.h" #include "tree-dump.h" #include "tree-flow.h" #include "domwalk.h" #include "real.h" #include "tree-pass.h" #include "tree-ssa-propagate.h" #include "langhooks.h" #include "params.h" /* This file implements optimizations on the dominator tree. */ /* Structure for recording edge equivalences as well as any pending edge redirections during the dominator optimizer. Computing and storing the edge equivalences instead of creating them on-demand can save significant amounts of time, particularly for pathological cases involving switch statements. These structures live for a single iteration of the dominator optimizer in the edge's AUX field. At the end of an iteration we free each of these structures and update the AUX field to point to any requested redirection target (the code for updating the CFG and SSA graph for edge redirection expects redirection edge targets to be in the AUX field for each edge. */ struct edge_info { /* If this edge creates a simple equivalence, the LHS and RHS of the equivalence will be stored here. */ tree lhs; tree rhs; /* Traversing an edge may also indicate one or more particular conditions are true or false. The number of recorded conditions can vary, but can be determined by the condition's code. So we have an array and its maximum index rather than use a varray. */ tree *cond_equivalences; unsigned int max_cond_equivalences; }; /* Hash table with expressions made available during the renaming process. When an assignment of the form X_i = EXPR is found, the statement is stored in this table. If the same expression EXPR is later found on the RHS of another statement, it is replaced with X_i (thus performing global redundancy elimination). Similarly as we pass through conditionals we record the conditional itself as having either a true or false value in this table. */ static htab_t avail_exprs; /* Stack of available expressions in AVAIL_EXPRs. Each block pushes any expressions it enters into the hash table along with a marker entry (null). When we finish processing the block, we pop off entries and remove the expressions from the global hash table until we hit the marker. */ static VEC(tree,heap) *avail_exprs_stack; /* Stack of statements we need to rescan during finalization for newly exposed variables. Statement rescanning must occur after the current block's available expressions are removed from AVAIL_EXPRS. Else we may change the hash code for an expression and be unable to find/remove it from AVAIL_EXPRS. */ static VEC(tree,heap) *stmts_to_rescan; /* Structure for entries in the expression hash table. This requires more memory for the hash table entries, but allows us to avoid creating silly tree nodes and annotations for conditionals, eliminates 2 global hash tables and two block local varrays. It also allows us to reduce the number of hash table lookups we have to perform in lookup_avail_expr and finally it allows us to significantly reduce the number of calls into the hashing routine itself. */ struct expr_hash_elt { /* The value (lhs) of this expression. */ tree lhs; /* The expression (rhs) we want to record. */ tree rhs; /* The stmt pointer if this element corresponds to a statement. */ tree stmt; /* The hash value for RHS/ann. */ hashval_t hash; }; /* Stack of dest,src pairs that need to be restored during finalization. A NULL entry is used to mark the end of pairs which need to be restored during finalization of this block. */ static VEC(tree,heap) *const_and_copies_stack; /* Bitmap of SSA_NAMEs known to have a nonzero value, even if we do not know their exact value. */ static bitmap nonzero_vars; /* Stack of SSA_NAMEs which need their NONZERO_VARS property cleared when the current block is finalized. A NULL entry is used to mark the end of names needing their entry in NONZERO_VARS cleared during finalization of this block. */ static VEC(tree,heap) *nonzero_vars_stack; /* Track whether or not we have changed the control flow graph. */ static bool cfg_altered; /* Bitmap of blocks that have had EH statements cleaned. We should remove their dead edges eventually. */ static bitmap need_eh_cleanup; /* Statistics for dominator optimizations. */ struct opt_stats_d { long num_stmts; long num_exprs_considered; long num_re; long num_const_prop; long num_copy_prop; }; static struct opt_stats_d opt_stats; struct eq_expr_value { tree src; tree dst; }; /* Local functions. */ static void optimize_stmt (struct dom_walk_data *, basic_block bb, block_stmt_iterator); static tree lookup_avail_expr (tree, bool); static hashval_t avail_expr_hash (const void *); static hashval_t real_avail_expr_hash (const void *); static int avail_expr_eq (const void *, const void *); static void htab_statistics (FILE *, htab_t); static void record_cond (tree, tree); static void record_const_or_copy (tree, tree); static void record_equality (tree, tree); static void record_equivalences_from_phis (basic_block); static void record_equivalences_from_incoming_edge (basic_block); static bool eliminate_redundant_computations (tree); static void record_equivalences_from_stmt (tree, int, stmt_ann_t); static void dom_thread_across_edge (struct dom_walk_data *, edge); static void dom_opt_finalize_block (struct dom_walk_data *, basic_block); static void dom_opt_initialize_block (struct dom_walk_data *, basic_block); static void propagate_to_outgoing_edges (struct dom_walk_data *, basic_block); static void remove_local_expressions_from_table (void); static void restore_vars_to_original_value (void); static edge single_incoming_edge_ignoring_loop_edges (basic_block); static void restore_nonzero_vars_to_original_value (void); static inline bool unsafe_associative_fp_binop (tree); /* Allocate an EDGE_INFO for edge E and attach it to E. Return the new EDGE_INFO structure. */ static struct edge_info * allocate_edge_info (edge e) { struct edge_info *edge_info; edge_info = XCNEW (struct edge_info); e->aux = edge_info; return edge_info; } /* Free all EDGE_INFO structures associated with edges in the CFG. If a particular edge can be threaded, copy the redirection target from the EDGE_INFO structure into the edge's AUX field as required by code to update the CFG and SSA graph for jump threading. */ static void free_all_edge_infos (void) { basic_block bb; edge_iterator ei; edge e; FOR_EACH_BB (bb) { FOR_EACH_EDGE (e, ei, bb->preds) { struct edge_info *edge_info = (struct edge_info *) e->aux; if (edge_info) { if (edge_info->cond_equivalences) free (edge_info->cond_equivalences); free (edge_info); e->aux = NULL; } } } } /* Jump threading, redundancy elimination and const/copy propagation. This pass may expose new symbols that need to be renamed into SSA. For every new symbol exposed, its corresponding bit will be set in VARS_TO_RENAME. */ static void tree_ssa_dominator_optimize (void) { struct dom_walk_data walk_data; unsigned int i; struct loops loops_info; memset (&opt_stats, 0, sizeof (opt_stats)); /* Create our hash tables. */ avail_exprs = htab_create (1024, real_avail_expr_hash, avail_expr_eq, free); avail_exprs_stack = VEC_alloc (tree, heap, 20); const_and_copies_stack = VEC_alloc (tree, heap, 20); nonzero_vars_stack = VEC_alloc (tree, heap, 20); stmts_to_rescan = VEC_alloc (tree, heap, 20); nonzero_vars = BITMAP_ALLOC (NULL); need_eh_cleanup = BITMAP_ALLOC (NULL); /* Setup callbacks for the generic dominator tree walker. */ walk_data.walk_stmts_backward = false; walk_data.dom_direction = CDI_DOMINATORS; walk_data.initialize_block_local_data = NULL; walk_data.before_dom_children_before_stmts = dom_opt_initialize_block; walk_data.before_dom_children_walk_stmts = optimize_stmt; walk_data.before_dom_children_after_stmts = propagate_to_outgoing_edges; walk_data.after_dom_children_before_stmts = NULL; walk_data.after_dom_children_walk_stmts = NULL; walk_data.after_dom_children_after_stmts = dom_opt_finalize_block; /* Right now we only attach a dummy COND_EXPR to the global data pointer. When we attach more stuff we'll need to fill this out with a real structure. */ walk_data.global_data = NULL; walk_data.block_local_data_size = 0; walk_data.interesting_blocks = NULL; /* Now initialize the dominator walker. */ init_walk_dominator_tree (&walk_data); calculate_dominance_info (CDI_DOMINATORS); /* We need to know which edges exit loops so that we can aggressively thread through loop headers to an exit edge. */ flow_loops_find (&loops_info); mark_loop_exit_edges (&loops_info); flow_loops_free (&loops_info); /* Clean up the CFG so that any forwarder blocks created by loop canonicalization are removed. */ cleanup_tree_cfg (); calculate_dominance_info (CDI_DOMINATORS); /* We need accurate information regarding back edges in the CFG for jump threading. */ mark_dfs_back_edges (); /* Recursively walk the dominator tree optimizing statements. */ walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR); { block_stmt_iterator bsi; basic_block bb; FOR_EACH_BB (bb) { for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi)) update_stmt_if_modified (bsi_stmt (bsi)); } } /* If we exposed any new variables, go ahead and put them into SSA form now, before we handle jump threading. This simplifies interactions between rewriting of _DECL nodes into SSA form and rewriting SSA_NAME nodes into SSA form after block duplication and CFG manipulation. */ update_ssa (TODO_update_ssa); free_all_edge_infos (); /* Thread jumps, creating duplicate blocks as needed. */ cfg_altered |= thread_through_all_blocks (); /* Removal of statements may make some EH edges dead. Purge such edges from the CFG as needed. */ if (!bitmap_empty_p (need_eh_cleanup)) { cfg_altered |= tree_purge_all_dead_eh_edges (need_eh_cleanup); bitmap_zero (need_eh_cleanup); } if (cfg_altered) free_dominance_info (CDI_DOMINATORS); /* Finally, remove everything except invariants in SSA_NAME_VALUE. Long term we will be able to let everything in SSA_NAME_VALUE persist. However, for now, we know this is the safe thing to do. */ for (i = 0; i < num_ssa_names; i++) { tree name = ssa_name (i); tree value; if (!name) continue; value = SSA_NAME_VALUE (name); if (value && !is_gimple_min_invariant (value)) SSA_NAME_VALUE (name) = NULL; } /* Debugging dumps. */ if (dump_file && (dump_flags & TDF_STATS)) dump_dominator_optimization_stats (dump_file); /* Delete our main hashtable. */ htab_delete (avail_exprs); /* And finalize the dominator walker. */ fini_walk_dominator_tree (&walk_data); /* Free nonzero_vars. */ BITMAP_FREE (nonzero_vars); BITMAP_FREE (need_eh_cleanup); VEC_free (tree, heap, avail_exprs_stack); VEC_free (tree, heap, const_and_copies_stack); VEC_free (tree, heap, nonzero_vars_stack); VEC_free (tree, heap, stmts_to_rescan); } static bool gate_dominator (void) { return flag_tree_dom != 0; } struct tree_opt_pass pass_dominator = { "dom", /* name */ gate_dominator, /* gate */ tree_ssa_dominator_optimize, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ TV_TREE_SSA_DOMINATOR_OPTS, /* tv_id */ PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_update_ssa | TODO_cleanup_cfg | TODO_verify_ssa, /* todo_flags_finish */ 0 /* letter */ }; /* Given a stmt CONDSTMT containing a COND_EXPR, canonicalize the COND_EXPR into a canonical form. */ static void canonicalize_comparison (tree condstmt) { tree cond = COND_EXPR_COND (condstmt); tree op0; tree op1; enum tree_code code = TREE_CODE (cond); if (!COMPARISON_CLASS_P (cond)) return; op0 = TREE_OPERAND (cond, 0); op1 = TREE_OPERAND (cond, 1); /* If it would be profitable to swap the operands, then do so to canonicalize the statement, enabling better optimization. By placing canonicalization of such expressions here we transparently keep statements in canonical form, even when the statement is modified. */ if (tree_swap_operands_p (op0, op1, false)) { /* For relationals we need to swap the operands and change the code. */ if (code == LT_EXPR || code == GT_EXPR || code == LE_EXPR || code == GE_EXPR) { TREE_SET_CODE (cond, swap_tree_comparison (code)); swap_tree_operands (condstmt, &TREE_OPERAND (cond, 0), &TREE_OPERAND (cond, 1)); /* If one operand was in the operand cache, but the other is not, because it is a constant, this is a case that the internal updating code of swap_tree_operands can't handle properly. */ if (TREE_CODE_CLASS (TREE_CODE (op0)) != TREE_CODE_CLASS (TREE_CODE (op1))) update_stmt (condstmt); } } } /* Initialize local stacks for this optimizer and record equivalences upon entry to BB. Equivalences can come from the edge traversed to reach BB or they may come from PHI nodes at the start of BB. */ static void dom_opt_initialize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, basic_block bb) { if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, "\n\nOptimizing block #%d\n\n", bb->index); /* Push a marker on the stacks of local information so that we know how far to unwind when we finalize this block. */ VEC_safe_push (tree, heap, avail_exprs_stack, NULL_TREE); VEC_safe_push (tree, heap, const_and_copies_stack, NULL_TREE); VEC_safe_push (tree, heap, nonzero_vars_stack, NULL_TREE); record_equivalences_from_incoming_edge (bb); /* PHI nodes can create equivalences too. */ record_equivalences_from_phis (bb); } /* Given an expression EXPR (a relational expression or a statement), initialize the hash table element pointed to by ELEMENT. */ static void initialize_hash_element (tree expr, tree lhs, struct expr_hash_elt *element) { /* Hash table elements may be based on conditional expressions or statements. For the former case, we have no annotation and we want to hash the conditional expression. In the latter case we have an annotation and we want to record the expression the statement evaluates. */ if (COMPARISON_CLASS_P (expr) || TREE_CODE (expr) == TRUTH_NOT_EXPR) { element->stmt = NULL; element->rhs = expr; } else if (TREE_CODE (expr) == COND_EXPR) { element->stmt = expr; element->rhs = COND_EXPR_COND (expr); } else if (TREE_CODE (expr) == SWITCH_EXPR) { element->stmt = expr; element->rhs = SWITCH_COND (expr); } else if (TREE_CODE (expr) == RETURN_EXPR && TREE_OPERAND (expr, 0)) { element->stmt = expr; element->rhs = TREE_OPERAND (TREE_OPERAND (expr, 0), 1); } else if (TREE_CODE (expr) == GOTO_EXPR) { element->stmt = expr; element->rhs = GOTO_DESTINATION (expr); } else { element->stmt = expr; element->rhs = TREE_OPERAND (expr, 1); } element->lhs = lhs; element->hash = avail_expr_hash (element); } /* Remove all the expressions in LOCALS from TABLE, stopping when there are LIMIT entries left in LOCALs. */ static void remove_local_expressions_from_table (void) { /* Remove all the expressions made available in this block. */ while (VEC_length (tree, avail_exprs_stack) > 0) { struct expr_hash_elt element; tree expr = VEC_pop (tree, avail_exprs_stack); if (expr == NULL_TREE) break; initialize_hash_element (expr, NULL, &element); htab_remove_elt_with_hash (avail_exprs, &element, element.hash); } } /* Use the SSA_NAMES in LOCALS to restore TABLE to its original state, stopping when there are LIMIT entries left in LOCALs. */ static void restore_nonzero_vars_to_original_value (void) { while (VEC_length (tree, nonzero_vars_stack) > 0) { tree name = VEC_pop (tree, nonzero_vars_stack); if (name == NULL) break; bitmap_clear_bit (nonzero_vars, SSA_NAME_VERSION (name)); } } /* Use the source/dest pairs in CONST_AND_COPIES_STACK to restore CONST_AND_COPIES to its original state, stopping when we hit a NULL marker. */ static void restore_vars_to_original_value (void) { while (VEC_length (tree, const_and_copies_stack) > 0) { tree prev_value, dest; dest = VEC_pop (tree, const_and_copies_stack); if (dest == NULL) break; prev_value = VEC_pop (tree, const_and_copies_stack); SSA_NAME_VALUE (dest) = prev_value; } } /* A trivial wrapper so that we can present the generic jump threading code with a simple API for simplifying statements. */ static tree simplify_stmt_for_jump_threading (tree stmt) { return lookup_avail_expr (stmt, false); } /* Wrapper for common code to attempt to thread an edge. For example, it handles lazily building the dummy condition and the bookkeeping when jump threading is successful. */ static void dom_thread_across_edge (struct dom_walk_data *walk_data, edge e) { /* If we don't already have a dummy condition, build it now. */ if (! walk_data->global_data) { tree dummy_cond = build2 (NE_EXPR, boolean_type_node, integer_zero_node, integer_zero_node); dummy_cond = build3 (COND_EXPR, void_type_node, dummy_cond, NULL, NULL); walk_data->global_data = dummy_cond; } thread_across_edge (walk_data->global_data, e, false, &const_and_copies_stack, simplify_stmt_for_jump_threading); } /* We have finished processing the dominator children of BB, perform any finalization actions in preparation for leaving this node in the dominator tree. */ static void dom_opt_finalize_block (struct dom_walk_data *walk_data, basic_block bb) { tree last; /* If we have an outgoing edge to a block with multiple incoming and outgoing edges, then we may be able to thread the edge. ie, we may be able to statically determine which of the outgoing edges will be traversed when the incoming edge from BB is traversed. */ if (single_succ_p (bb) && (single_succ_edge (bb)->flags & EDGE_ABNORMAL) == 0 && potentially_threadable_block (single_succ (bb))) { dom_thread_across_edge (walk_data, single_succ_edge (bb)); } else if ((last = last_stmt (bb)) && TREE_CODE (last) == COND_EXPR && (COMPARISON_CLASS_P (COND_EXPR_COND (last)) || TREE_CODE (COND_EXPR_COND (last)) == SSA_NAME) && EDGE_COUNT (bb->succs) == 2 && (EDGE_SUCC (bb, 0)->flags & EDGE_ABNORMAL) == 0 && (EDGE_SUCC (bb, 1)->flags & EDGE_ABNORMAL) == 0) { edge true_edge, false_edge; extract_true_false_edges_from_block (bb, &true_edge, &false_edge); /* Only try to thread the edge if it reaches a target block with more than one predecessor and more than one successor. */ if (potentially_threadable_block (true_edge->dest)) { struct edge_info *edge_info; unsigned int i; /* Push a marker onto the available expression stack so that we unwind any expressions related to the TRUE arm before processing the false arm below. */ VEC_safe_push (tree, heap, avail_exprs_stack, NULL_TREE); VEC_safe_push (tree, heap, const_and_copies_stack, NULL_TREE); edge_info = (struct edge_info *) true_edge->aux; /* If we have info associated with this edge, record it into our equivalency tables. */ if (edge_info) { tree *cond_equivalences = edge_info->cond_equivalences; tree lhs = edge_info->lhs; tree rhs = edge_info->rhs; /* If we have a simple NAME = VALUE equivalency record it. */ if (lhs && TREE_CODE (lhs) == SSA_NAME) record_const_or_copy (lhs, rhs); /* If we have 0 = COND or 1 = COND equivalences, record them into our expression hash tables. */ if (cond_equivalences) for (i = 0; i < edge_info->max_cond_equivalences; i += 2) { tree expr = cond_equivalences[i]; tree value = cond_equivalences[i + 1]; record_cond (expr, value); } } dom_thread_across_edge (walk_data, true_edge); /* And restore the various tables to their state before we threaded this edge. */ remove_local_expressions_from_table (); } /* Similarly for the ELSE arm. */ if (potentially_threadable_block (false_edge->dest)) { struct edge_info *edge_info; unsigned int i; VEC_safe_push (tree, heap, const_and_copies_stack, NULL_TREE); edge_info = (struct edge_info *) false_edge->aux; /* If we have info associated with this edge, record it into our equivalency tables. */ if (edge_info) { tree *cond_equivalences = edge_info->cond_equivalences; tree lhs = edge_info->lhs; tree rhs = edge_info->rhs; /* If we have a simple NAME = VALUE equivalency record it. */ if (lhs && TREE_CODE (lhs) == SSA_NAME) record_const_or_copy (lhs, rhs); /* If we have 0 = COND or 1 = COND equivalences, record them into our expression hash tables. */ if (cond_equivalences) for (i = 0; i < edge_info->max_cond_equivalences; i += 2) { tree expr = cond_equivalences[i]; tree value = cond_equivalences[i + 1]; record_cond (expr, value); } } /* Now thread the edge. */ dom_thread_across_edge (walk_data, false_edge); /* No need to remove local expressions from our tables or restore vars to their original value as that will be done immediately below. */ } } remove_local_expressions_from_table (); restore_nonzero_vars_to_original_value (); restore_vars_to_original_value (); /* If we queued any statements to rescan in this block, then go ahead and rescan them now. */ while (VEC_length (tree, stmts_to_rescan) > 0) { tree stmt = VEC_last (tree, stmts_to_rescan); basic_block stmt_bb = bb_for_stmt (stmt); if (stmt_bb != bb) break; VEC_pop (tree, stmts_to_rescan); mark_new_vars_to_rename (stmt); } } /* PHI nodes can create equivalences too. Ignoring any alternatives which are the same as the result, if all the alternatives are equal, then the PHI node creates an equivalence. Additionally, if all the PHI alternatives are known to have a nonzero value, then the result of this PHI is known to have a nonzero value, even if we do not know its exact value. */ static void record_equivalences_from_phis (basic_block bb) { tree phi; for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) { tree lhs = PHI_RESULT (phi); tree rhs = NULL; int i; for (i = 0; i < PHI_NUM_ARGS (phi); i++) { tree t = PHI_ARG_DEF (phi, i); /* Ignore alternatives which are the same as our LHS. Since LHS is a PHI_RESULT, it is known to be a SSA_NAME, so we can simply compare pointers. */ if (lhs == t) continue; /* If we have not processed an alternative yet, then set RHS to this alternative. */ if (rhs == NULL) rhs = t; /* If we have processed an alternative (stored in RHS), then see if it is equal to this one. If it isn't, then stop the search. */ else if (! operand_equal_for_phi_arg_p (rhs, t)) break; } /* If we had no interesting alternatives, then all the RHS alternatives must have been the same as LHS. */ if (!rhs) rhs = lhs; /* If we managed to iterate through each PHI alternative without breaking out of the loop, then we have a PHI which may create a useful equivalence. We do not need to record unwind data for this, since this is a true assignment and not an equivalence inferred from a comparison. All uses of this ssa name are dominated by this assignment, so unwinding just costs time and space. */ if (i == PHI_NUM_ARGS (phi) && may_propagate_copy (lhs, rhs)) SSA_NAME_VALUE (lhs) = rhs; /* Now see if we know anything about the nonzero property for the result of this PHI. */ for (i = 0; i < PHI_NUM_ARGS (phi); i++) { if (!PHI_ARG_NONZERO (phi, i)) break; } if (i == PHI_NUM_ARGS (phi)) bitmap_set_bit (nonzero_vars, SSA_NAME_VERSION (PHI_RESULT (phi))); } } /* Ignoring loop backedges, if BB has precisely one incoming edge then return that edge. Otherwise return NULL. */ static edge single_incoming_edge_ignoring_loop_edges (basic_block bb) { edge retval = NULL; edge e; edge_iterator ei; FOR_EACH_EDGE (e, ei, bb->preds) { /* A loop back edge can be identified by the destination of the edge dominating the source of the edge. */ if (dominated_by_p (CDI_DOMINATORS, e->src, e->dest)) continue; /* If we have already seen a non-loop edge, then we must have multiple incoming non-loop edges and thus we return NULL. */ if (retval) return NULL; /* This is the first non-loop incoming edge we have found. Record it. */ retval = e; } return retval; } /* Record any equivalences created by the incoming edge to BB. If BB has more than one incoming edge, then no equivalence is created. */ static void record_equivalences_from_incoming_edge (basic_block bb) { edge e; basic_block parent; struct edge_info *edge_info; /* If our parent block ended with a control statement, then we may be able to record some equivalences based on which outgoing edge from the parent was followed. */ parent = get_immediate_dominator (CDI_DOMINATORS, bb); e = single_incoming_edge_ignoring_loop_edges (bb); /* If we had a single incoming edge from our parent block, then enter any data associated with the edge into our tables. */ if (e && e->src == parent) { unsigned int i; edge_info = (struct edge_info *) e->aux; if (edge_info) { tree lhs = edge_info->lhs; tree rhs = edge_info->rhs; tree *cond_equivalences = edge_info->cond_equivalences; if (lhs) record_equality (lhs, rhs); if (cond_equivalences) { for (i = 0; i < edge_info->max_cond_equivalences; i += 2) { tree expr = cond_equivalences[i]; tree value = cond_equivalences[i + 1]; record_cond (expr, value); } } } } } /* Dump SSA statistics on FILE. */ void dump_dominator_optimization_stats (FILE *file) { long n_exprs; fprintf (file, "Total number of statements: %6ld\n\n", opt_stats.num_stmts); fprintf (file, "Exprs considered for dominator optimizations: %6ld\n", opt_stats.num_exprs_considered); n_exprs = opt_stats.num_exprs_considered; if (n_exprs == 0) n_exprs = 1; fprintf (file, " Redundant expressions eliminated: %6ld (%.0f%%)\n", opt_stats.num_re, PERCENT (opt_stats.num_re, n_exprs)); fprintf (file, " Constants propagated: %6ld\n", opt_stats.num_const_prop); fprintf (file, " Copies propagated: %6ld\n", opt_stats.num_copy_prop); fprintf (file, "\nHash table statistics:\n"); fprintf (file, " avail_exprs: "); htab_statistics (file, avail_exprs); } /* Dump SSA statistics on stderr. */ void debug_dominator_optimization_stats (void) { dump_dominator_optimization_stats (stderr); } /* Dump statistics for the hash table HTAB. */ static void htab_statistics (FILE *file, htab_t htab) { fprintf (file, "size %ld, %ld elements, %f collision/search ratio\n", (long) htab_size (htab), (long) htab_elements (htab), htab_collisions (htab)); } /* Record the fact that VAR has a nonzero value, though we may not know its exact value. Note that if VAR is already known to have a nonzero value, then we do nothing. */ static void record_var_is_nonzero (tree var) { int indx = SSA_NAME_VERSION (var); if (bitmap_bit_p (nonzero_vars, indx)) return; /* Mark it in the global table. */ bitmap_set_bit (nonzero_vars, indx); /* Record this SSA_NAME so that we can reset the global table when we leave this block. */ VEC_safe_push (tree, heap, nonzero_vars_stack, var); } /* Enter a statement into the true/false expression hash table indicating that the condition COND has the value VALUE. */ static void record_cond (tree cond, tree value) { struct expr_hash_elt *element = XCNEW (struct expr_hash_elt); void **slot; initialize_hash_element (cond, value, element); slot = htab_find_slot_with_hash (avail_exprs, (void *)element, element->hash, INSERT); if (*slot == NULL) { *slot = (void *) element; VEC_safe_push (tree, heap, avail_exprs_stack, cond); } else free (element); } /* Build a new conditional using NEW_CODE, OP0 and OP1 and store the new conditional into *p, then store a boolean_true_node into *(p + 1). */ static void build_and_record_new_cond (enum tree_code new_code, tree op0, tree op1, tree *p) { *p = build2 (new_code, boolean_type_node, op0, op1); p++; *p = boolean_true_node; } /* Record that COND is true and INVERTED is false into the edge information structure. Also record that any conditions dominated by COND are true as well. For example, if a < b is true, then a <= b must also be true. */ static void record_conditions (struct edge_info *edge_info, tree cond, tree inverted) { tree op0, op1; if (!COMPARISON_CLASS_P (cond)) return; op0 = TREE_OPERAND (cond, 0); op1 = TREE_OPERAND (cond, 1); switch (TREE_CODE (cond)) { case LT_EXPR: case GT_EXPR: edge_info->max_cond_equivalences = 12; edge_info->cond_equivalences = XNEWVEC (tree, 12); build_and_record_new_cond ((TREE_CODE (cond) == LT_EXPR ? LE_EXPR : GE_EXPR), op0, op1, &edge_info->cond_equivalences[4]); build_and_record_new_cond (ORDERED_EXPR, op0, op1, &edge_info->cond_equivalences[6]); build_and_record_new_cond (NE_EXPR, op0, op1, &edge_info->cond_equivalences[8]); build_and_record_new_cond (LTGT_EXPR, op0, op1, &edge_info->cond_equivalences[10]); break; case GE_EXPR: case LE_EXPR: edge_info->max_cond_equivalences = 6; edge_info->cond_equivalences = XNEWVEC (tree, 6); build_and_record_new_cond (ORDERED_EXPR, op0, op1, &edge_info->cond_equivalences[4]); break; case EQ_EXPR: edge_info->max_cond_equivalences = 10; edge_info->cond_equivalences = XNEWVEC (tree, 10); build_and_record_new_cond (ORDERED_EXPR, op0, op1, &edge_info->cond_equivalences[4]); build_and_record_new_cond (LE_EXPR, op0, op1, &edge_info->cond_equivalences[6]); build_and_record_new_cond (GE_EXPR, op0, op1, &edge_info->cond_equivalences[8]); break; case UNORDERED_EXPR: edge_info->max_cond_equivalences = 16; edge_info->cond_equivalences = XNEWVEC (tree, 16); build_and_record_new_cond (NE_EXPR, op0, op1, &edge_info->cond_equivalences[4]); build_and_record_new_cond (UNLE_EXPR, op0, op1, &edge_info->cond_equivalences[6]); build_and_record_new_cond (UNGE_EXPR, op0, op1, &edge_info->cond_equivalences[8]); build_and_record_new_cond (UNEQ_EXPR, op0, op1, &edge_info->cond_equivalences[10]); build_and_record_new_cond (UNLT_EXPR, op0, op1, &edge_info->cond_equivalences[12]); build_and_record_new_cond (UNGT_EXPR, op0, op1, &edge_info->cond_equivalences[14]); break; case UNLT_EXPR: case UNGT_EXPR: edge_info->max_cond_equivalences = 8; edge_info->cond_equivalences = XNEWVEC (tree, 8); build_and_record_new_cond ((TREE_CODE (cond) == UNLT_EXPR ? UNLE_EXPR : UNGE_EXPR), op0, op1, &edge_info->cond_equivalences[4]); build_and_record_new_cond (NE_EXPR, op0, op1, &edge_info->cond_equivalences[6]); break; case UNEQ_EXPR: edge_info->max_cond_equivalences = 8; edge_info->cond_equivalences = XNEWVEC (tree, 8); build_and_record_new_cond (UNLE_EXPR, op0, op1, &edge_info->cond_equivalences[4]); build_and_record_new_cond (UNGE_EXPR, op0, op1, &edge_info->cond_equivalences[6]); break; case LTGT_EXPR: edge_info->max_cond_equivalences = 8; edge_info->cond_equivalences = XNEWVEC (tree, 8); build_and_record_new_cond (NE_EXPR, op0, op1, &edge_info->cond_equivalences[4]); build_and_record_new_cond (ORDERED_EXPR, op0, op1, &edge_info->cond_equivalences[6]); break; default: edge_info->max_cond_equivalences = 4; edge_info->cond_equivalences = XNEWVEC (tree, 4); break; } /* Now store the original true and false conditions into the first two slots. */ edge_info->cond_equivalences[0] = cond; edge_info->cond_equivalences[1] = boolean_true_node; edge_info->cond_equivalences[2] = inverted; edge_info->cond_equivalences[3] = boolean_false_node; } /* A helper function for record_const_or_copy and record_equality. Do the work of recording the value and undo info. */ static void record_const_or_copy_1 (tree x, tree y, tree prev_x) { SSA_NAME_VALUE (x) = y; VEC_reserve (tree, heap, const_and_copies_stack, 2); VEC_quick_push (tree, const_and_copies_stack, prev_x); VEC_quick_push (tree, const_and_copies_stack, x); } /* Return the loop depth of the basic block of the defining statement of X. This number should not be treated as absolutely correct because the loop information may not be completely up-to-date when dom runs. However, it will be relatively correct, and as more passes are taught to keep loop info up to date, the result will become more and more accurate. */ int loop_depth_of_name (tree x) { tree defstmt; basic_block defbb; /* If it's not an SSA_NAME, we have no clue where the definition is. */ if (TREE_CODE (x) != SSA_NAME) return 0; /* Otherwise return the loop depth of the defining statement's bb. Note that there may not actually be a bb for this statement, if the ssa_name is live on entry. */ defstmt = SSA_NAME_DEF_STMT (x); defbb = bb_for_stmt (defstmt); if (!defbb) return 0; return defbb->loop_depth; } /* Record that X is equal to Y in const_and_copies. Record undo information in the block-local vector. */ static void record_const_or_copy (tree x, tree y) { tree prev_x = SSA_NAME_VALUE (x); if (TREE_CODE (y) == SSA_NAME) { tree tmp = SSA_NAME_VALUE (y); if (tmp) y = tmp; } record_const_or_copy_1 (x, y, prev_x); } /* Similarly, but assume that X and Y are the two operands of an EQ_EXPR. This constrains the cases in which we may treat this as assignment. */ static void record_equality (tree x, tree y) { tree prev_x = NULL, prev_y = NULL; if (TREE_CODE (x) == SSA_NAME) prev_x = SSA_NAME_VALUE (x); if (TREE_CODE (y) == SSA_NAME) prev_y = SSA_NAME_VALUE (y); /* If one of the previous values is invariant, or invariant in more loops (by depth), then use that. Otherwise it doesn't matter which value we choose, just so long as we canonicalize on one value. */ if (TREE_INVARIANT (y)) ; else if (TREE_INVARIANT (x) || (loop_depth_of_name (x) <= loop_depth_of_name (y))) prev_x = x, x = y, y = prev_x, prev_x = prev_y; else if (prev_x && TREE_INVARIANT (prev_x)) x = y, y = prev_x, prev_x = prev_y; else if (prev_y && TREE_CODE (prev_y) != VALUE_HANDLE) y = prev_y; /* After the swapping, we must have one SSA_NAME. */ if (TREE_CODE (x) != SSA_NAME) return; /* For IEEE, -0.0 == 0.0, so we don't necessarily know the sign of a variable compared against zero. If we're honoring signed zeros, then we cannot record this value unless we know that the value is nonzero. */ if (HONOR_SIGNED_ZEROS (TYPE_MODE (TREE_TYPE (x))) && (TREE_CODE (y) != REAL_CST || REAL_VALUES_EQUAL (dconst0, TREE_REAL_CST (y)))) return; record_const_or_copy_1 (x, y, prev_x); } /* Return true, if it is ok to do folding of an associative expression. EXP is the tree for the associative expression. */ static inline bool unsafe_associative_fp_binop (tree exp) { enum tree_code code = TREE_CODE (exp); return !(!flag_unsafe_math_optimizations && (code == MULT_EXPR || code == PLUS_EXPR || code == MINUS_EXPR) && FLOAT_TYPE_P (TREE_TYPE (exp))); } /* Returns true when STMT is a simple iv increment. It detects the following situation: i_1 = phi (..., i_2) i_2 = i_1 +/- ... */ static bool simple_iv_increment_p (tree stmt) { tree lhs, rhs, preinc, phi; unsigned i; if (TREE_CODE (stmt) != MODIFY_EXPR) return false; lhs = TREE_OPERAND (stmt, 0); if (TREE_CODE (lhs) != SSA_NAME) return false; rhs = TREE_OPERAND (stmt, 1); if (TREE_CODE (rhs) != PLUS_EXPR && TREE_CODE (rhs) != MINUS_EXPR) return false; preinc = TREE_OPERAND (rhs, 0); if (TREE_CODE (preinc) != SSA_NAME) return false; phi = SSA_NAME_DEF_STMT (preinc); if (TREE_CODE (phi) != PHI_NODE) return false; for (i = 0; i < (unsigned) PHI_NUM_ARGS (phi); i++) if (PHI_ARG_DEF (phi, i) == lhs) return true; return false; } /* CONST_AND_COPIES is a table which maps an SSA_NAME to the current known value for that SSA_NAME (or NULL if no value is known). NONZERO_VARS is the set SSA_NAMES known to have a nonzero value, even if we don't know their precise value. Propagate values from CONST_AND_COPIES and NONZERO_VARS into the PHI nodes of the successors of BB. */ static void cprop_into_successor_phis (basic_block bb, bitmap nonzero_vars) { edge e; edge_iterator ei; FOR_EACH_EDGE (e, ei, bb->succs) { tree phi; int indx; /* If this is an abnormal edge, then we do not want to copy propagate into the PHI alternative associated with this edge. */ if (e->flags & EDGE_ABNORMAL) continue; phi = phi_nodes (e->dest); if (! phi) continue; indx = e->dest_idx; for ( ; phi; phi = PHI_CHAIN (phi)) { tree new; use_operand_p orig_p; tree orig; /* The alternative may be associated with a constant, so verify it is an SSA_NAME before doing anything with it. */ orig_p = PHI_ARG_DEF_PTR (phi, indx); orig = USE_FROM_PTR (orig_p); if (TREE_CODE (orig) != SSA_NAME) continue; /* If the alternative is known to have a nonzero value, record that fact in the PHI node itself for future use. */ if (bitmap_bit_p (nonzero_vars, SSA_NAME_VERSION (orig))) PHI_ARG_NONZERO (phi, indx) = true; /* If we have *ORIG_P in our constant/copy table, then replace ORIG_P with its value in our constant/copy table. */ new = SSA_NAME_VALUE (orig); if (new && new != orig && (TREE_CODE (new) == SSA_NAME || is_gimple_min_invariant (new)) && may_propagate_copy (orig, new)) propagate_value (orig_p, new); } } } /* We have finished optimizing BB, record any information implied by taking a specific outgoing edge from BB. */ static void record_edge_info (basic_block bb) { block_stmt_iterator bsi = bsi_last (bb); struct edge_info *edge_info; if (! bsi_end_p (bsi)) { tree stmt = bsi_stmt (bsi); if (stmt && TREE_CODE (stmt) == SWITCH_EXPR) { tree cond = SWITCH_COND (stmt); if (TREE_CODE (cond) == SSA_NAME) { tree labels = SWITCH_LABELS (stmt); int i, n_labels = TREE_VEC_LENGTH (labels); tree *info = XCNEWVEC (tree, last_basic_block); edge e; edge_iterator ei; for (i = 0; i < n_labels; i++) { tree label = TREE_VEC_ELT (labels, i); basic_block target_bb = label_to_block (CASE_LABEL (label)); if (CASE_HIGH (label) || !CASE_LOW (label) || info[target_bb->index]) info[target_bb->index] = error_mark_node; else info[target_bb->index] = label; } FOR_EACH_EDGE (e, ei, bb->succs) { basic_block target_bb = e->dest; tree node = info[target_bb->index]; if (node != NULL && node != error_mark_node) { tree x = fold_convert (TREE_TYPE (cond), CASE_LOW (node)); edge_info = allocate_edge_info (e); edge_info->lhs = cond; edge_info->rhs = x; } } free (info); } } /* A COND_EXPR may create equivalences too. */ if (stmt && TREE_CODE (stmt) == COND_EXPR) { tree cond = COND_EXPR_COND (stmt); edge true_edge; edge false_edge; extract_true_false_edges_from_block (bb, &true_edge, &false_edge); /* If the conditional is a single variable 'X', record 'X = 1' for the true edge and 'X = 0' on the false edge. */ if (SSA_VAR_P (cond)) { struct edge_info *edge_info; edge_info = allocate_edge_info (true_edge); edge_info->lhs = cond; edge_info->rhs = constant_boolean_node (1, TREE_TYPE (cond)); edge_info = allocate_edge_info (false_edge); edge_info->lhs = cond; edge_info->rhs = constant_boolean_node (0, TREE_TYPE (cond)); } /* Equality tests may create one or two equivalences. */ else if (COMPARISON_CLASS_P (cond)) { tree op0 = TREE_OPERAND (cond, 0); tree op1 = TREE_OPERAND (cond, 1); /* Special case comparing booleans against a constant as we know the value of OP0 on both arms of the branch. i.e., we can record an equivalence for OP0 rather than COND. */ if ((TREE_CODE (cond) == EQ_EXPR || TREE_CODE (cond) == NE_EXPR) && TREE_CODE (op0) == SSA_NAME && TREE_CODE (TREE_TYPE (op0)) == BOOLEAN_TYPE && is_gimple_min_invariant (op1)) { if (TREE_CODE (cond) == EQ_EXPR) { edge_info = allocate_edge_info (true_edge); edge_info->lhs = op0; edge_info->rhs = (integer_zerop (op1) ? boolean_false_node : boolean_true_node); edge_info = allocate_edge_info (false_edge); edge_info->lhs = op0; edge_info->rhs = (integer_zerop (op1) ? boolean_true_node : boolean_false_node); } else { edge_info = allocate_edge_info (true_edge); edge_info->lhs = op0; edge_info->rhs = (integer_zerop (op1) ? boolean_true_node : boolean_false_node); edge_info = allocate_edge_info (false_edge); edge_info->lhs = op0; edge_info->rhs = (integer_zerop (op1) ? boolean_false_node : boolean_true_node); } } else if (is_gimple_min_invariant (op0) && (TREE_CODE (op1) == SSA_NAME || is_gimple_min_invariant (op1))) { tree inverted = invert_truthvalue (cond); struct edge_info *edge_info; edge_info = allocate_edge_info (true_edge); record_conditions (edge_info, cond, inverted); if (TREE_CODE (cond) == EQ_EXPR) { edge_info->lhs = op1; edge_info->rhs = op0; } edge_info = allocate_edge_info (false_edge); record_conditions (edge_info, inverted, cond); if (TREE_CODE (cond) == NE_EXPR) { edge_info->lhs = op1; edge_info->rhs = op0; } } else if (TREE_CODE (op0) == SSA_NAME && (is_gimple_min_invariant (op1) || TREE_CODE (op1) == SSA_NAME)) { tree inverted = invert_truthvalue (cond); struct edge_info *edge_info; edge_info = allocate_edge_info (true_edge); record_conditions (edge_info, cond, inverted); if (TREE_CODE (cond) == EQ_EXPR) { edge_info->lhs = op0; edge_info->rhs = op1; } edge_info = allocate_edge_info (false_edge); record_conditions (edge_info, inverted, cond); if (TREE_CODE (cond) == NE_EXPR) { edge_info->lhs = op0; edge_info->rhs = op1; } } } /* ??? TRUTH_NOT_EXPR can create an equivalence too. */ } } } /* Propagate information from BB to its outgoing edges. This can include equivalency information implied by control statements at the end of BB and const/copy propagation into PHIs in BB's successor blocks. */ static void propagate_to_outgoing_edges (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, basic_block bb) { record_edge_info (bb); cprop_into_successor_phis (bb, nonzero_vars); } /* Search for redundant computations in STMT. If any are found, then replace them with the variable holding the result of the computation. If safe, record this expression into the available expression hash table. */ static bool eliminate_redundant_computations (tree stmt) { tree *expr_p, def = NULL_TREE; bool insert = true; tree cached_lhs; bool retval = false; bool modify_expr_p = false; if (TREE_CODE (stmt) == MODIFY_EXPR) def = TREE_OPERAND (stmt, 0); /* Certain expressions on the RHS can be optimized away, but can not themselves be entered into the hash tables. */ if (! def || TREE_CODE (def) != SSA_NAME || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def) || !ZERO_SSA_OPERANDS (stmt, SSA_OP_VMAYDEF) /* Do not record equivalences for increments of ivs. This would create overlapping live ranges for a very questionable gain. */ || simple_iv_increment_p (stmt)) insert = false; /* Check if the expression has been computed before. */ cached_lhs = lookup_avail_expr (stmt, insert); opt_stats.num_exprs_considered++; /* Get a pointer to the expression we are trying to optimize. */ if (TREE_CODE (stmt) == COND_EXPR) expr_p = &COND_EXPR_COND (stmt); else if (TREE_CODE (stmt) == SWITCH_EXPR) expr_p = &SWITCH_COND (stmt); else if (TREE_CODE (stmt) == RETURN_EXPR && TREE_OPERAND (stmt, 0)) { expr_p = &TREE_OPERAND (TREE_OPERAND (stmt, 0), 1); modify_expr_p = true; } else { expr_p = &TREE_OPERAND (stmt, 1); modify_expr_p = true; } /* It is safe to ignore types here since we have already done type checking in the hashing and equality routines. In fact type checking here merely gets in the way of constant propagation. Also, make sure that it is safe to propagate CACHED_LHS into *EXPR_P. */ if (cached_lhs && ((TREE_CODE (cached_lhs) != SSA_NAME && (modify_expr_p || tree_ssa_useless_type_conversion_1 (TREE_TYPE (*expr_p), TREE_TYPE (cached_lhs)))) || may_propagate_copy (*expr_p, cached_lhs))) { if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, " Replaced redundant expr '"); print_generic_expr (dump_file, *expr_p, dump_flags); fprintf (dump_file, "' with '"); print_generic_expr (dump_file, cached_lhs, dump_flags); fprintf (dump_file, "'\n"); } opt_stats.num_re++; #if defined ENABLE_CHECKING gcc_assert (TREE_CODE (cached_lhs) == SSA_NAME || is_gimple_min_invariant (cached_lhs)); #endif if (TREE_CODE (cached_lhs) == ADDR_EXPR || (POINTER_TYPE_P (TREE_TYPE (*expr_p)) && is_gimple_min_invariant (cached_lhs))) retval = true; if (modify_expr_p && !tree_ssa_useless_type_conversion_1 (TREE_TYPE (*expr_p), TREE_TYPE (cached_lhs))) cached_lhs = fold_convert (TREE_TYPE (*expr_p), cached_lhs); propagate_tree_value (expr_p, cached_lhs); mark_stmt_modified (stmt); } return retval; } /* STMT, a MODIFY_EXPR, may create certain equivalences, in either the available expressions table or the const_and_copies table. Detect and record those equivalences. */ static void record_equivalences_from_stmt (tree stmt, int may_optimize_p, stmt_ann_t ann) { tree lhs = TREE_OPERAND (stmt, 0); enum tree_code lhs_code = TREE_CODE (lhs); int i; if (lhs_code == SSA_NAME) { tree rhs = TREE_OPERAND (stmt, 1); /* Strip away any useless type conversions. */ STRIP_USELESS_TYPE_CONVERSION (rhs); /* If the RHS of the assignment is a constant or another variable that may be propagated, register it in the CONST_AND_COPIES table. We do not need to record unwind data for this, since this is a true assignment and not an equivalence inferred from a comparison. All uses of this ssa name are dominated by this assignment, so unwinding just costs time and space. */ if (may_optimize_p && (TREE_CODE (rhs) == SSA_NAME || is_gimple_min_invariant (rhs))) SSA_NAME_VALUE (lhs) = rhs; if (tree_expr_nonzero_p (rhs)) record_var_is_nonzero (lhs); } /* Look at both sides for pointer dereferences. If we find one, then the pointer must be nonnull and we can enter that equivalence into the hash tables. */ if (flag_delete_null_pointer_checks) for (i = 0; i < 2; i++) { tree t = TREE_OPERAND (stmt, i); /* Strip away any COMPONENT_REFs. */ while (TREE_CODE (t) == COMPONENT_REF) t = TREE_OPERAND (t, 0); /* Now see if this is a pointer dereference. */ if (INDIRECT_REF_P (t)) { tree op = TREE_OPERAND (t, 0); /* If the pointer is a SSA variable, then enter new equivalences into the hash table. */ while (TREE_CODE (op) == SSA_NAME) { tree def = SSA_NAME_DEF_STMT (op); record_var_is_nonzero (op); /* And walk up the USE-DEF chains noting other SSA_NAMEs which are known to have a nonzero value. */ if (def && TREE_CODE (def) == MODIFY_EXPR && TREE_CODE (TREE_OPERAND (def, 1)) == NOP_EXPR) op = TREE_OPERAND (TREE_OPERAND (def, 1), 0); else break; } } } /* A memory store, even an aliased store, creates a useful equivalence. By exchanging the LHS and RHS, creating suitable vops and recording the result in the available expression table, we may be able to expose more redundant loads. */ if (!ann->has_volatile_ops && (TREE_CODE (TREE_OPERAND (stmt, 1)) == SSA_NAME || is_gimple_min_invariant (TREE_OPERAND (stmt, 1))) && !is_gimple_reg (lhs)) { tree rhs = TREE_OPERAND (stmt, 1); tree new; /* FIXME: If the LHS of the assignment is a bitfield and the RHS is a constant, we need to adjust the constant to fit into the type of the LHS. If the LHS is a bitfield and the RHS is not a constant, then we can not record any equivalences for this statement since we would need to represent the widening or narrowing of RHS. This fixes gcc.c-torture/execute/921016-1.c and should not be necessary if GCC represented bitfields properly. */ if (lhs_code == COMPONENT_REF && DECL_BIT_FIELD (TREE_OPERAND (lhs, 1))) { if (TREE_CONSTANT (rhs)) rhs = widen_bitfield (rhs, TREE_OPERAND (lhs, 1), lhs); else rhs = NULL; /* If the value overflowed, then we can not use this equivalence. */ if (rhs && ! is_gimple_min_invariant (rhs)) rhs = NULL; } if (rhs) { /* Build a new statement with the RHS and LHS exchanged. */ new = build2 (MODIFY_EXPR, TREE_TYPE (stmt), rhs, lhs); create_ssa_artficial_load_stmt (new, stmt); /* Finally enter the statement into the available expression table. */ lookup_avail_expr (new, true); } } } /* Replace *OP_P in STMT with any known equivalent value for *OP_P from CONST_AND_COPIES. */ static bool cprop_operand (tree stmt, use_operand_p op_p) { bool may_have_exposed_new_symbols = false; tree val; tree op = USE_FROM_PTR (op_p); /* If the operand has a known constant value or it is known to be a copy of some other variable, use the value or copy stored in CONST_AND_COPIES. */ val = SSA_NAME_VALUE (op); if (val && val != op && TREE_CODE (val) != VALUE_HANDLE) { tree op_type, val_type; /* Do not change the base variable in the virtual operand tables. That would make it impossible to reconstruct the renamed virtual operand if we later modify this statement. Also only allow the new value to be an SSA_NAME for propagation into virtual operands. */ if (!is_gimple_reg (op) && (TREE_CODE (val) != SSA_NAME || is_gimple_reg (val) || get_virtual_var (val) != get_virtual_var (op))) return false; /* Do not replace hard register operands in asm statements. */ if (TREE_CODE (stmt) == ASM_EXPR && !may_propagate_copy_into_asm (op)) return false; /* Get the toplevel type of each operand. */ op_type = TREE_TYPE (op); val_type = TREE_TYPE (val); /* While both types are pointers, get the type of the object pointed to. */ while (POINTER_TYPE_P (op_type) && POINTER_TYPE_P (val_type)) { op_type = TREE_TYPE (op_type); val_type = TREE_TYPE (val_type); } /* Make sure underlying types match before propagating a constant by converting the constant to the proper type. Note that convert may return a non-gimple expression, in which case we ignore this propagation opportunity. */ if (TREE_CODE (val) != SSA_NAME) { if (!lang_hooks.types_compatible_p (op_type, val_type)) { val = fold_convert (TREE_TYPE (op), val); if (!is_gimple_min_invariant (val)) return false; } } /* Certain operands are not allowed to be copy propagated due to their interaction with exception handling and some GCC extensions. */ else if (!may_propagate_copy (op, val)) return false; /* Do not propagate copies if the propagated value is at a deeper loop depth than the propagatee. Otherwise, this may move loop variant variables outside of their loops and prevent coalescing opportunities. If the value was loop invariant, it will be hoisted by LICM and exposed for copy propagation. */ if (loop_depth_of_name (val) > loop_depth_of_name (op)) return false; /* Dump details. */ if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, " Replaced '"); print_generic_expr (dump_file, op, dump_flags); fprintf (dump_file, "' with %s '", (TREE_CODE (val) != SSA_NAME ? "constant" : "variable")); print_generic_expr (dump_file, val, dump_flags); fprintf (dump_file, "'\n"); } /* If VAL is an ADDR_EXPR or a constant of pointer type, note that we may have exposed a new symbol for SSA renaming. */ if (TREE_CODE (val) == ADDR_EXPR || (POINTER_TYPE_P (TREE_TYPE (op)) && is_gimple_min_invariant (val))) may_have_exposed_new_symbols = true; if (TREE_CODE (val) != SSA_NAME) opt_stats.num_const_prop++; else opt_stats.num_copy_prop++; propagate_value (op_p, val); /* And note that we modified this statement. This is now safe, even if we changed virtual operands since we will rescan the statement and rewrite its operands again. */ mark_stmt_modified (stmt); } return may_have_exposed_new_symbols; } /* CONST_AND_COPIES is a table which maps an SSA_NAME to the current known value for that SSA_NAME (or NULL if no value is known). Propagate values from CONST_AND_COPIES into the uses, vuses and v_may_def_ops of STMT. */ static bool cprop_into_stmt (tree stmt) { bool may_have_exposed_new_symbols = false; use_operand_p op_p; ssa_op_iter iter; FOR_EACH_SSA_USE_OPERAND (op_p, stmt, iter, SSA_OP_ALL_USES) { if (TREE_CODE (USE_FROM_PTR (op_p)) == SSA_NAME) may_have_exposed_new_symbols |= cprop_operand (stmt, op_p); } return may_have_exposed_new_symbols; } /* Optimize the statement pointed to by iterator SI. We try to perform some simplistic global redundancy elimination and constant propagation: 1- To detect global redundancy, we keep track of expressions that have been computed in this block and its dominators. If we find that the same expression is computed more than once, we eliminate repeated computations by using the target of the first one. 2- Constant values and copy assignments. This is used to do very simplistic constant and copy propagation. When a constant or copy assignment is found, we map the value on the RHS of the assignment to the variable in the LHS in the CONST_AND_COPIES table. */ static void optimize_stmt (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, basic_block bb, block_stmt_iterator si) { stmt_ann_t ann; tree stmt, old_stmt; bool may_optimize_p; bool may_have_exposed_new_symbols = false; old_stmt = stmt = bsi_stmt (si); if (TREE_CODE (stmt) == COND_EXPR) canonicalize_comparison (stmt); update_stmt_if_modified (stmt); ann = stmt_ann (stmt); opt_stats.num_stmts++; may_have_exposed_new_symbols = false; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Optimizing statement "); print_generic_stmt (dump_file, stmt, TDF_SLIM); } /* Const/copy propagate into USES, VUSES and the RHS of V_MAY_DEFs. */ may_have_exposed_new_symbols = cprop_into_stmt (stmt); /* If the statement has been modified with constant replacements, fold its RHS before checking for redundant computations. */ if (ann->modified) { tree rhs; /* Try to fold the statement making sure that STMT is kept up to date. */ if (fold_stmt (bsi_stmt_ptr (si))) { stmt = bsi_stmt (si); ann = stmt_ann (stmt); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, " Folded to: "); print_generic_stmt (dump_file, stmt, TDF_SLIM); } } rhs = get_rhs (stmt); if (rhs && TREE_CODE (rhs) == ADDR_EXPR) recompute_tree_invariant_for_addr_expr (rhs); /* Constant/copy propagation above may change the set of virtual operands associated with this statement. Folding may remove the need for some virtual operands. Indicate we will need to rescan and rewrite the statement. */ may_have_exposed_new_symbols = true; } /* Check for redundant computations. Do this optimization only for assignments that have no volatile ops and conditionals. */ may_optimize_p = (!ann->has_volatile_ops && ((TREE_CODE (stmt) == RETURN_EXPR && TREE_OPERAND (stmt, 0) && TREE_CODE (TREE_OPERAND (stmt, 0)) == MODIFY_EXPR && ! (TREE_SIDE_EFFECTS (TREE_OPERAND (TREE_OPERAND (stmt, 0), 1)))) || (TREE_CODE (stmt) == MODIFY_EXPR && ! TREE_SIDE_EFFECTS (TREE_OPERAND (stmt, 1))) || TREE_CODE (stmt) == COND_EXPR || TREE_CODE (stmt) == SWITCH_EXPR)); if (may_optimize_p) may_have_exposed_new_symbols |= eliminate_redundant_computations (stmt); /* Record any additional equivalences created by this statement. */ if (TREE_CODE (stmt) == MODIFY_EXPR) record_equivalences_from_stmt (stmt, may_optimize_p, ann); /* If STMT is a COND_EXPR and it was modified, then we may know where it goes. If that is the case, then mark the CFG as altered. This will cause us to later call remove_unreachable_blocks and cleanup_tree_cfg when it is safe to do so. It is not safe to clean things up here since removal of edges and such can trigger the removal of PHI nodes, which in turn can release SSA_NAMEs to the manager. That's all fine and good, except that once SSA_NAMEs are released to the manager, we must not call create_ssa_name until all references to released SSA_NAMEs have been eliminated. All references to the deleted SSA_NAMEs can not be eliminated until we remove unreachable blocks. We can not remove unreachable blocks until after we have completed any queued jump threading. We can not complete any queued jump threads until we have taken appropriate variables out of SSA form. Taking variables out of SSA form can call create_ssa_name and thus we lose. Ultimately I suspect we're going to need to change the interface into the SSA_NAME manager. */ if (ann->modified) { tree val = NULL; if (TREE_CODE (stmt) == COND_EXPR) val = COND_EXPR_COND (stmt); else if (TREE_CODE (stmt) == SWITCH_EXPR) val = SWITCH_COND (stmt); if (val && TREE_CODE (val) == INTEGER_CST && find_taken_edge (bb, val)) cfg_altered = true; /* If we simplified a statement in such a way as to be shown that it cannot trap, update the eh information and the cfg to match. */ if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt)) { bitmap_set_bit (need_eh_cleanup, bb->index); if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, " Flagged to clear EH edges.\n"); } } if (may_have_exposed_new_symbols) VEC_safe_push (tree, heap, stmts_to_rescan, bsi_stmt (si)); } /* Search for an existing instance of STMT in the AVAIL_EXPRS table. If found, return its LHS. Otherwise insert STMT in the table and return NULL_TREE. Also, when an expression is first inserted in the AVAIL_EXPRS table, it is also added to the stack pointed to by BLOCK_AVAIL_EXPRS_P, so that they can be removed when we finish processing this block and its children. NOTE: This function assumes that STMT is a MODIFY_EXPR node that contains no CALL_EXPR on its RHS and makes no volatile nor aliased references. */ static tree lookup_avail_expr (tree stmt, bool insert) { void **slot; tree lhs; tree temp; struct expr_hash_elt *element = XNEW (struct expr_hash_elt); lhs = TREE_CODE (stmt) == MODIFY_EXPR ? TREE_OPERAND (stmt, 0) : NULL; initialize_hash_element (stmt, lhs, element); /* Don't bother remembering constant assignments and copy operations. Constants and copy operations are handled by the constant/copy propagator in optimize_stmt. */ if (TREE_CODE (element->rhs) == SSA_NAME || is_gimple_min_invariant (element->rhs)) { free (element); return NULL_TREE; } /* If this is an equality test against zero, see if we have recorded a nonzero value for the variable in question. */ if ((TREE_CODE (element->rhs) == EQ_EXPR || TREE_CODE (element->rhs) == NE_EXPR) && TREE_CODE (TREE_OPERAND (element->rhs, 0)) == SSA_NAME && integer_zerop (TREE_OPERAND (element->rhs, 1))) { int indx = SSA_NAME_VERSION (TREE_OPERAND (element->rhs, 0)); if (bitmap_bit_p (nonzero_vars, indx)) { tree t = element->rhs; free (element); return constant_boolean_node (TREE_CODE (t) != EQ_EXPR, TREE_TYPE (t)); } } /* Finally try to find the expression in the main expression hash table. */ slot = htab_find_slot_with_hash (avail_exprs, element, element->hash, (insert ? INSERT : NO_INSERT)); if (slot == NULL) { free (element); return NULL_TREE; } if (*slot == NULL) { *slot = (void *) element; VEC_safe_push (tree, heap, avail_exprs_stack, stmt ? stmt : element->rhs); return NULL_TREE; } /* Extract the LHS of the assignment so that it can be used as the current definition of another variable. */ lhs = ((struct expr_hash_elt *)*slot)->lhs; /* See if the LHS appears in the CONST_AND_COPIES table. If it does, then use the value from the const_and_copies table. */ if (TREE_CODE (lhs) == SSA_NAME) { temp = SSA_NAME_VALUE (lhs); if (temp && TREE_CODE (temp) != VALUE_HANDLE) lhs = temp; } free (element); return lhs; } /* Hashing and equality functions for AVAIL_EXPRS. The table stores MODIFY_EXPR statements. We compute a value number for expressions using the code of the expression and the SSA numbers of its operands. */ static hashval_t avail_expr_hash (const void *p) { tree stmt = ((struct expr_hash_elt *)p)->stmt; tree rhs = ((struct expr_hash_elt *)p)->rhs; tree vuse; ssa_op_iter iter; hashval_t val = 0; /* iterative_hash_expr knows how to deal with any expression and deals with commutative operators as well, so just use it instead of duplicating such complexities here. */ val = iterative_hash_expr (rhs, val); /* If the hash table entry is not associated with a statement, then we can just hash the expression and not worry about virtual operands and such. */ if (!stmt || !stmt_ann (stmt)) return val; /* Add the SSA version numbers of every vuse operand. This is important because compound variables like arrays are not renamed in the operands. Rather, the rename is done on the virtual variable representing all the elements of the array. */ FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, iter, SSA_OP_VUSE) val = iterative_hash_expr (vuse, val); return val; } static hashval_t real_avail_expr_hash (const void *p) { return ((const struct expr_hash_elt *)p)->hash; } static int avail_expr_eq (const void *p1, const void *p2) { tree stmt1 = ((struct expr_hash_elt *)p1)->stmt; tree rhs1 = ((struct expr_hash_elt *)p1)->rhs; tree stmt2 = ((struct expr_hash_elt *)p2)->stmt; tree rhs2 = ((struct expr_hash_elt *)p2)->rhs; /* If they are the same physical expression, return true. */ if (rhs1 == rhs2 && stmt1 == stmt2) return true; /* If their codes are not equal, then quit now. */ if (TREE_CODE (rhs1) != TREE_CODE (rhs2)) return false; /* In case of a collision, both RHS have to be identical and have the same VUSE operands. */ if ((TREE_TYPE (rhs1) == TREE_TYPE (rhs2) || lang_hooks.types_compatible_p (TREE_TYPE (rhs1), TREE_TYPE (rhs2))) && operand_equal_p (rhs1, rhs2, OEP_PURE_SAME)) { bool ret = compare_ssa_operands_equal (stmt1, stmt2, SSA_OP_VUSE); gcc_assert (!ret || ((struct expr_hash_elt *)p1)->hash == ((struct expr_hash_elt *)p2)->hash); return ret; } return false; }