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Diffstat (limited to 'gcc-4.2.1-5666.3/gcc/tree-ssa-dom.c')
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1 files changed, 2531 insertions, 0 deletions
diff --git a/gcc-4.2.1-5666.3/gcc/tree-ssa-dom.c b/gcc-4.2.1-5666.3/gcc/tree-ssa-dom.c new file mode 100644 index 000000000..88f7399ed --- /dev/null +++ b/gcc-4.2.1-5666.3/gcc/tree-ssa-dom.c @@ -0,0 +1,2531 @@ +/* SSA Dominator optimizations for trees + Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006 + Free Software Foundation, Inc. + Contributed by Diego Novillo <dnovillo@redhat.com> + +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; + +/* 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); + + +/* 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 unsigned int +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); + stmts_to_rescan = VEC_alloc (tree, heap, 20); + 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 asserted bitmaps and stacks. */ + BITMAP_FREE (need_eh_cleanup); + + VEC_free (tree, heap, avail_exprs_stack); + VEC_free (tree, heap, const_and_copies_stack); + VEC_free (tree, heap, stmts_to_rescan); + return 0; +} + +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 */ + PROP_smt_usage, /* properties_destroyed */ + 0, /* todo_flags_start */ + TODO_dump_func + | TODO_update_ssa + | TODO_cleanup_cfg + | TODO_verify_ssa + | TODO_update_smt_usage, /* 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); + + 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 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, tree within_stmt ATTRIBUTE_UNUSED) +{ + 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_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. */ + +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; + } +} + +/* 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)); +} + +/* 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: + if (FLOAT_TYPE_P (TREE_TYPE (op0))) + { + edge_info->max_cond_equivalences = 12; + edge_info->cond_equivalences = XNEWVEC (tree, 12); + build_and_record_new_cond (ORDERED_EXPR, op0, op1, + &edge_info->cond_equivalences[8]); + build_and_record_new_cond (LTGT_EXPR, op0, op1, + &edge_info->cond_equivalences[10]); + } + else + { + edge_info->max_cond_equivalences = 8; + edge_info->cond_equivalences = XNEWVEC (tree, 8); + } + + 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 (NE_EXPR, op0, op1, + &edge_info->cond_equivalences[6]); + break; + + case GE_EXPR: + case LE_EXPR: + if (FLOAT_TYPE_P (TREE_TYPE (op0))) + { + 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]); + } + else + { + edge_info->max_cond_equivalences = 4; + edge_info->cond_equivalences = XNEWVEC (tree, 4); + } + break; + + case EQ_EXPR: + if (FLOAT_TYPE_P (TREE_TYPE (op0))) + { + 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[8]); + } + else + { + edge_info->max_cond_equivalences = 8; + edge_info->cond_equivalences = XNEWVEC (tree, 8); + } + build_and_record_new_cond (LE_EXPR, op0, op1, + &edge_info->cond_equivalences[4]); + build_and_record_new_cond (GE_EXPR, op0, op1, + &edge_info->cond_equivalences[6]); + 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); +} + +/* 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). + + Propagate values from CONST_AND_COPIES into the PHI nodes of the + successors of BB. */ + +static void +cprop_into_successor_phis (basic_block bb) +{ + 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 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); +} + +/* 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); + + 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; + } + + /* 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; + } + + /* 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; +} + +/* PHI-ONLY copy and constant propagation. This pass is meant to clean + up degenerate PHIs created by or exposed by jump threading. */ + +/* Given PHI, return its RHS if the PHI is a degenerate, otherwise return + NULL. */ + +static tree +degenerate_phi_result (tree phi) +{ + tree lhs = PHI_RESULT (phi); + tree val = NULL; + int i; + + /* Ignoring arguments which are the same as LHS, if all the remaining + arguments are the same, then the PHI is a degenerate and has the + value of that common argument. */ + for (i = 0; i < PHI_NUM_ARGS (phi); i++) + { + tree arg = PHI_ARG_DEF (phi, i); + + if (arg == lhs) + continue; + else if (!val) + val = arg; + else if (!operand_equal_p (arg, val, 0)) + break; + } + return (i == PHI_NUM_ARGS (phi) ? val : NULL); +} + +/* Given a tree node T, which is either a PHI_NODE or MODIFY_EXPR, + remove it from the IL. */ + +static void +remove_stmt_or_phi (tree t) +{ + if (TREE_CODE (t) == PHI_NODE) + remove_phi_node (t, NULL); + else + { + block_stmt_iterator bsi = bsi_for_stmt (t); + bsi_remove (&bsi, true); + } +} + +/* Given a tree node T, which is either a PHI_NODE or MODIFY_EXPR, + return the "rhs" of the node, in the case of a non-degenerate + PHI, NULL is returned. */ + +static tree +get_rhs_or_phi_arg (tree t) +{ + if (TREE_CODE (t) == PHI_NODE) + return degenerate_phi_result (t); + else if (TREE_CODE (t) == MODIFY_EXPR) + return TREE_OPERAND (t, 1); + gcc_unreachable (); +} + + +/* Given a tree node T, which is either a PHI_NODE or a MODIFY_EXPR, + return the "lhs" of the node. */ + +static tree +get_lhs_or_phi_result (tree t) +{ + if (TREE_CODE (t) == PHI_NODE) + return PHI_RESULT (t); + else if (TREE_CODE (t) == MODIFY_EXPR) + return TREE_OPERAND (t, 0); + gcc_unreachable (); +} + +/* Propagate RHS into all uses of LHS (when possible). + + RHS and LHS are derived from STMT, which is passed in solely so + that we can remove it if propagation is successful. + + When propagating into a PHI node or into a statement which turns + into a trivial copy or constant initialization, set the + appropriate bit in INTERESTING_NAMEs so that we will visit those + nodes as well in an effort to pick up secondary optimization + opportunities. */ + +static void +propagate_rhs_into_lhs (tree stmt, tree lhs, tree rhs, bitmap interesting_names) +{ + /* First verify that propagation is valid and isn't going to move a + loop variant variable outside its loop. */ + if (! SSA_NAME_OCCURS_IN_ABNORMAL_PHI (lhs) + && (TREE_CODE (rhs) != SSA_NAME + || ! SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs)) + && may_propagate_copy (lhs, rhs) + && loop_depth_of_name (lhs) >= loop_depth_of_name (rhs)) + { + use_operand_p use_p; + imm_use_iterator iter; + tree use_stmt; + bool all = true; + + /* Dump details. */ + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, " Replacing '"); + print_generic_expr (dump_file, lhs, dump_flags); + fprintf (dump_file, "' with %s '", + (TREE_CODE (rhs) != SSA_NAME ? "constant" : "variable")); + print_generic_expr (dump_file, rhs, dump_flags); + fprintf (dump_file, "'\n"); + } + + /* Walk over every use of LHS and try to replace the use with RHS. + At this point the only reason why such a propagation would not + be successful would be if the use occurs in an ASM_EXPR. */ + FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs) + { + + /* It's not always safe to propagate into an ASM_EXPR. */ + if (TREE_CODE (use_stmt) == ASM_EXPR + && ! may_propagate_copy_into_asm (lhs)) + { + all = false; + continue; + } + + /* Dump details. */ + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, " Original statement:"); + print_generic_expr (dump_file, use_stmt, dump_flags); + fprintf (dump_file, "\n"); + } + + /* Propagate the RHS into this use of the LHS. */ + FOR_EACH_IMM_USE_ON_STMT (use_p, iter) + propagate_value (use_p, rhs); + + /* Special cases to avoid useless calls into the folding + routines, operand scanning, etc. + + First, propagation into a PHI may cause the PHI to become + a degenerate, so mark the PHI as interesting. No other + actions are necessary. + + Second, if we're propagating a virtual operand and the + propagation does not change the underlying _DECL node for + the virtual operand, then no further actions are necessary. */ + if (TREE_CODE (use_stmt) == PHI_NODE + || (! is_gimple_reg (lhs) + && TREE_CODE (rhs) == SSA_NAME + && SSA_NAME_VAR (lhs) == SSA_NAME_VAR (rhs))) + { + /* Dump details. */ + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, " Updated statement:"); + print_generic_expr (dump_file, use_stmt, dump_flags); + fprintf (dump_file, "\n"); + } + + /* Propagation into a PHI may expose new degenerate PHIs, + so mark the result of the PHI as interesting. */ + if (TREE_CODE (use_stmt) == PHI_NODE) + { + tree result = get_lhs_or_phi_result (use_stmt); + bitmap_set_bit (interesting_names, SSA_NAME_VERSION (result)); + } + continue; + } + + /* From this point onward we are propagating into a + real statement. Folding may (or may not) be possible, + we may expose new operands, expose dead EH edges, + etc. */ + fold_stmt_inplace (use_stmt); + + /* Sometimes propagation can expose new operands to the + renamer. Note this will call update_stmt at the + appropriate time. */ + mark_new_vars_to_rename (use_stmt); + + /* Dump details. */ + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, " Updated statement:"); + print_generic_expr (dump_file, use_stmt, dump_flags); + fprintf (dump_file, "\n"); + } + + /* If we replaced a variable index with a constant, then + we would need to update the invariant flag for ADDR_EXPRs. */ + if (TREE_CODE (use_stmt) == MODIFY_EXPR + && TREE_CODE (TREE_OPERAND (use_stmt, 1)) == ADDR_EXPR) + recompute_tree_invariant_for_addr_expr (TREE_OPERAND (use_stmt, 1)); + + /* If we cleaned up EH information from the statement, + mark its containing block as needing EH cleanups. */ + if (maybe_clean_or_replace_eh_stmt (use_stmt, use_stmt)) + { + bitmap_set_bit (need_eh_cleanup, bb_for_stmt (use_stmt)->index); + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, " Flagged to clear EH edges.\n"); + } + + /* Propagation may expose new trivial copy/constant propagation + opportunities. */ + if (TREE_CODE (use_stmt) == MODIFY_EXPR + && TREE_CODE (TREE_OPERAND (use_stmt, 0)) == SSA_NAME + && (TREE_CODE (TREE_OPERAND (use_stmt, 1)) == SSA_NAME + || is_gimple_min_invariant (TREE_OPERAND (use_stmt, 1)))) + { + tree result = get_lhs_or_phi_result (use_stmt); + bitmap_set_bit (interesting_names, SSA_NAME_VERSION (result)); + } + + /* Propagation into these nodes may make certain edges in + the CFG unexecutable. We want to identify them as PHI nodes + at the destination of those unexecutable edges may become + degenerates. */ + else if (TREE_CODE (use_stmt) == COND_EXPR + || TREE_CODE (use_stmt) == SWITCH_EXPR + || TREE_CODE (use_stmt) == GOTO_EXPR) + { + tree val; + + if (TREE_CODE (use_stmt) == COND_EXPR) + val = COND_EXPR_COND (use_stmt); + else if (TREE_CODE (use_stmt) == SWITCH_EXPR) + val = SWITCH_COND (use_stmt); + else + val = GOTO_DESTINATION (use_stmt); + + if (is_gimple_min_invariant (val)) + { + basic_block bb = bb_for_stmt (use_stmt); + edge te = find_taken_edge (bb, val); + edge_iterator ei; + edge e; + block_stmt_iterator bsi; + + /* Remove all outgoing edges except TE. */ + for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei));) + { + if (e != te) + { + tree phi; + + /* Mark all the PHI nodes at the destination of + the unexecutable edge as interesting. */ + for (phi = phi_nodes (e->dest); + phi; + phi = PHI_CHAIN (phi)) + { + tree result = PHI_RESULT (phi); + int version = SSA_NAME_VERSION (result); + + bitmap_set_bit (interesting_names, version); + } + + te->probability += e->probability; + + te->count += e->count; + remove_edge (e); + cfg_altered = 1; + } + else + ei_next (&ei); + } + + bsi = bsi_last (bb_for_stmt (use_stmt)); + bsi_remove (&bsi, true); + + /* And fixup the flags on the single remaining edge. */ + te->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE); + te->flags &= ~EDGE_ABNORMAL; + te->flags |= EDGE_FALLTHRU; + if (te->probability > REG_BR_PROB_BASE) + te->probability = REG_BR_PROB_BASE; + } + } + } + + /* Ensure there is nothing else to do. */ + gcc_assert (!all || has_zero_uses (lhs)); + + /* If we were able to propagate away all uses of LHS, then + we can remove STMT. */ + if (all) + remove_stmt_or_phi (stmt); + } +} + +/* T is either a PHI node (potentially a degenerate PHI node) or + a statement that is a trivial copy or constant initialization. + + Attempt to eliminate T by propagating its RHS into all uses of + its LHS. This may in turn set new bits in INTERESTING_NAMES + for nodes we want to revisit later. + + All exit paths should clear INTERESTING_NAMES for the result + of T. */ + +static void +eliminate_const_or_copy (tree t, bitmap interesting_names) +{ + tree lhs = get_lhs_or_phi_result (t); + tree rhs; + int version = SSA_NAME_VERSION (lhs); + + /* If the LHS of this statement or PHI has no uses, then we can + just eliminate it. This can occur if, for example, the PHI + was created by block duplication due to threading and its only + use was in the conditional at the end of the block which was + deleted. */ + if (has_zero_uses (lhs)) + { + bitmap_clear_bit (interesting_names, version); + remove_stmt_or_phi (t); + return; + } + + /* Get the RHS of the assignment or PHI node if the PHI is a + degenerate. */ + rhs = get_rhs_or_phi_arg (t); + if (!rhs) + { + bitmap_clear_bit (interesting_names, version); + return; + } + + propagate_rhs_into_lhs (t, lhs, rhs, interesting_names); + + /* Note that T may well have been deleted by now, so do + not access it, instead use the saved version # to clear + T's entry in the worklist. */ + bitmap_clear_bit (interesting_names, version); +} + +/* The first phase in degenerate PHI elimination. + + Eliminate the degenerate PHIs in BB, then recurse on the + dominator children of BB. */ + +static void +eliminate_degenerate_phis_1 (basic_block bb, bitmap interesting_names) +{ + tree phi, next; + basic_block son; + + for (phi = phi_nodes (bb); phi; phi = next) + { + next = PHI_CHAIN (phi); + eliminate_const_or_copy (phi, interesting_names); + } + + /* Recurse into the dominator children of BB. */ + for (son = first_dom_son (CDI_DOMINATORS, bb); + son; + son = next_dom_son (CDI_DOMINATORS, son)) + eliminate_degenerate_phis_1 (son, interesting_names); +} + + +/* A very simple pass to eliminate degenerate PHI nodes from the + IL. This is meant to be fast enough to be able to be run several + times in the optimization pipeline. + + Certain optimizations, particularly those which duplicate blocks + or remove edges from the CFG can create or expose PHIs which are + trivial copies or constant initializations. + + While we could pick up these optimizations in DOM or with the + combination of copy-prop and CCP, those solutions are far too + heavy-weight for our needs. + + This implementation has two phases so that we can efficiently + eliminate the first order degenerate PHIs and second order + degenerate PHIs. + + The first phase performs a dominator walk to identify and eliminate + the vast majority of the degenerate PHIs. When a degenerate PHI + is identified and eliminated any affected statements or PHIs + are put on a worklist. + + The second phase eliminates degenerate PHIs and trivial copies + or constant initializations using the worklist. This is how we + pick up the secondary optimization opportunities with minimal + cost. */ + +static unsigned int +eliminate_degenerate_phis (void) +{ + bitmap interesting_names; + bitmap interesting_names1; + + /* Bitmap of blocks which need EH information updated. We can not + update it on-the-fly as doing so invalidates the dominator tree. */ + need_eh_cleanup = BITMAP_ALLOC (NULL); + + /* INTERESTING_NAMES is effectively our worklist, indexed by + SSA_NAME_VERSION. + + A set bit indicates that the statement or PHI node which + defines the SSA_NAME should be (re)examined to determine if + it has become a degenerate PHI or trivial const/copy propagation + opportunity. + + Experiments have show we generally get better compilation + time behavior with bitmaps rather than sbitmaps. */ + interesting_names = BITMAP_ALLOC (NULL); + interesting_names1 = BITMAP_ALLOC (NULL); + + /* First phase. Eliminate degenerate PHIs via a dominator + walk of the CFG. + + Experiments have indicated that we generally get better + compile-time behavior by visiting blocks in the first + phase in dominator order. Presumably this is because walking + in dominator order leaves fewer PHIs for later examination + by the worklist phase. */ + calculate_dominance_info (CDI_DOMINATORS); + eliminate_degenerate_phis_1 (ENTRY_BLOCK_PTR, interesting_names); + + /* Second phase. Eliminate second order degenerate PHIs as well + as trivial copies or constant initializations identified by + the first phase or this phase. Basically we keep iterating + until our set of INTERESTING_NAMEs is empty. */ + while (!bitmap_empty_p (interesting_names)) + { + unsigned int i; + bitmap_iterator bi; + + /* EXECUTE_IF_SET_IN_BITMAP does not like its bitmap + changed during the loop. Copy it to another bitmap and + use that. */ + bitmap_copy (interesting_names1, interesting_names); + + EXECUTE_IF_SET_IN_BITMAP (interesting_names1, 0, i, bi) + { + tree name = ssa_name (i); + + /* Ignore SSA_NAMEs that have been released because + their defining statement was deleted (unreachable). */ + if (name) + eliminate_const_or_copy (SSA_NAME_DEF_STMT (ssa_name (i)), + interesting_names); + } + } + + /* Propagation of const and copies 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_FREE (need_eh_cleanup); + } + + BITMAP_FREE (interesting_names); + BITMAP_FREE (interesting_names1); + if (cfg_altered) + free_dominance_info (CDI_DOMINATORS); + return 0; +} + +struct tree_opt_pass pass_phi_only_cprop = +{ + "phicprop", /* name */ + gate_dominator, /* gate */ + eliminate_degenerate_phis, /* execute */ + NULL, /* sub */ + NULL, /* next */ + 0, /* static_pass_number */ + TV_TREE_PHI_CPROP, /* tv_id */ + PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ + 0, /* properties_provided */ + PROP_smt_usage, /* properties_destroyed */ + 0, /* todo_flags_start */ + TODO_cleanup_cfg | TODO_dump_func + | TODO_ggc_collect | TODO_verify_ssa + | TODO_verify_stmts | TODO_update_smt_usage + | TODO_update_ssa, /* todo_flags_finish */ + 0 /* letter */ +}; |