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Diffstat (limited to 'gcc/tree-ssa-dce.c')
| -rw-r--r-- | gcc/tree-ssa-dce.c | 1016 |
1 files changed, 1016 insertions, 0 deletions
diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c new file mode 100644 index 0000000..684ea78 --- /dev/null +++ b/gcc/tree-ssa-dce.c @@ -0,0 +1,1016 @@ +/* Dead code elimination pass for the GNU compiler. + Copyright (C) 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc. + Contributed by Ben Elliston <bje@redhat.com> + and Andrew MacLeod <amacleod@redhat.com> + Adapted to use control dependence by Steven Bosscher, SUSE Labs. + +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. */ + +/* Dead code elimination. + + References: + + Building an Optimizing Compiler, + Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9. + + Advanced Compiler Design and Implementation, + Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10. + + Dead-code elimination is the removal of statements which have no + impact on the program's output. "Dead statements" have no impact + on the program's output, while "necessary statements" may have + impact on the output. + + The algorithm consists of three phases: + 1. Marking as necessary all statements known to be necessary, + e.g. most function calls, writing a value to memory, etc; + 2. Propagating necessary statements, e.g., the statements + giving values to operands in necessary statements; and + 3. Removing dead statements. */ + +#include "config.h" +#include "system.h" +#include "coretypes.h" +#include "tm.h" +#include "ggc.h" + +/* These RTL headers are needed for basic-block.h. */ +#include "rtl.h" +#include "tm_p.h" +#include "hard-reg-set.h" +#include "obstack.h" +#include "basic-block.h" + +#include "tree.h" +#include "diagnostic.h" +#include "tree-flow.h" +#include "tree-gimple.h" +#include "tree-dump.h" +#include "tree-pass.h" +#include "timevar.h" +#include "flags.h" +#include "cfgloop.h" +#include "tree-scalar-evolution.h" + +static struct stmt_stats +{ + int total; + int total_phis; + int removed; + int removed_phis; +} stats; + +static VEC(tree,heap) *worklist; + +/* Vector indicating an SSA name has already been processed and marked + as necessary. */ +static sbitmap processed; + +/* Vector indicating that last_stmt if a basic block has already been + marked as necessary. */ +static sbitmap last_stmt_necessary; + +/* Before we can determine whether a control branch is dead, we need to + compute which blocks are control dependent on which edges. + + We expect each block to be control dependent on very few edges so we + use a bitmap for each block recording its edges. An array holds the + bitmap. The Ith bit in the bitmap is set if that block is dependent + on the Ith edge. */ +static bitmap *control_dependence_map; + +/* Vector indicating that a basic block has already had all the edges + processed that it is control dependent on. */ +static sbitmap visited_control_parents; + +/* TRUE if this pass alters the CFG (by removing control statements). + FALSE otherwise. + + If this pass alters the CFG, then it will arrange for the dominators + to be recomputed. */ +static bool cfg_altered; + +/* Execute code that follows the macro for each edge (given number + EDGE_NUMBER within the CODE) for which the block with index N is + control dependent. */ +#define EXECUTE_IF_CONTROL_DEPENDENT(BI, N, EDGE_NUMBER) \ + EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[(N)], 0, \ + (EDGE_NUMBER), (BI)) + +/* Local function prototypes. */ +static inline void set_control_dependence_map_bit (basic_block, int); +static inline void clear_control_dependence_bitmap (basic_block); +static void find_all_control_dependences (struct edge_list *); +static void find_control_dependence (struct edge_list *, int); +static inline basic_block find_pdom (basic_block); + +static inline void mark_stmt_necessary (tree, bool); +static inline void mark_operand_necessary (tree, bool); + +static void mark_stmt_if_obviously_necessary (tree, bool); +static void find_obviously_necessary_stmts (struct edge_list *); + +static void mark_control_dependent_edges_necessary (basic_block, struct edge_list *); +static void propagate_necessity (struct edge_list *); + +static void eliminate_unnecessary_stmts (void); +static void remove_dead_phis (basic_block); +static void remove_dead_stmt (block_stmt_iterator *, basic_block); + +static void print_stats (void); +static void tree_dce_init (bool); +static void tree_dce_done (bool); + +/* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */ +static inline void +set_control_dependence_map_bit (basic_block bb, int edge_index) +{ + if (bb == ENTRY_BLOCK_PTR) + return; + gcc_assert (bb != EXIT_BLOCK_PTR); + bitmap_set_bit (control_dependence_map[bb->index], edge_index); +} + +/* Clear all control dependences for block BB. */ +static inline void +clear_control_dependence_bitmap (basic_block bb) +{ + bitmap_clear (control_dependence_map[bb->index]); +} + +/* Record all blocks' control dependences on all edges in the edge + list EL, ala Morgan, Section 3.6. */ + +static void +find_all_control_dependences (struct edge_list *el) +{ + int i; + + for (i = 0; i < NUM_EDGES (el); ++i) + find_control_dependence (el, i); +} + +/* Determine all blocks' control dependences on the given edge with edge_list + EL index EDGE_INDEX, ala Morgan, Section 3.6. */ + +static void +find_control_dependence (struct edge_list *el, int edge_index) +{ + basic_block current_block; + basic_block ending_block; + + gcc_assert (INDEX_EDGE_PRED_BB (el, edge_index) != EXIT_BLOCK_PTR); + + if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR) + ending_block = single_succ (ENTRY_BLOCK_PTR); + else + ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index)); + + for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index); + current_block != ending_block && current_block != EXIT_BLOCK_PTR; + current_block = find_pdom (current_block)) + { + edge e = INDEX_EDGE (el, edge_index); + + /* For abnormal edges, we don't make current_block control + dependent because instructions that throw are always necessary + anyway. */ + if (e->flags & EDGE_ABNORMAL) + continue; + + set_control_dependence_map_bit (current_block, edge_index); + } +} + +/* Find the immediate postdominator PDOM of the specified basic block BLOCK. + This function is necessary because some blocks have negative numbers. */ + +static inline basic_block +find_pdom (basic_block block) +{ + gcc_assert (block != ENTRY_BLOCK_PTR); + + if (block == EXIT_BLOCK_PTR) + return EXIT_BLOCK_PTR; + else + { + basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block); + if (! bb) + return EXIT_BLOCK_PTR; + return bb; + } +} + +#define NECESSARY(stmt) stmt->common.asm_written_flag + +/* If STMT is not already marked necessary, mark it, and add it to the + worklist if ADD_TO_WORKLIST is true. */ +static inline void +mark_stmt_necessary (tree stmt, bool add_to_worklist) +{ + gcc_assert (stmt); + gcc_assert (!DECL_P (stmt)); + + if (NECESSARY (stmt)) + return; + + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, "Marking useful stmt: "); + print_generic_stmt (dump_file, stmt, TDF_SLIM); + fprintf (dump_file, "\n"); + } + + NECESSARY (stmt) = 1; + if (add_to_worklist) + VEC_safe_push (tree, heap, worklist, stmt); +} + +/* Mark the statement defining operand OP as necessary. PHIONLY is true + if we should only mark it necessary if it is a phi node. */ + +static inline void +mark_operand_necessary (tree op, bool phionly) +{ + tree stmt; + int ver; + + gcc_assert (op); + + ver = SSA_NAME_VERSION (op); + if (TEST_BIT (processed, ver)) + return; + SET_BIT (processed, ver); + + stmt = SSA_NAME_DEF_STMT (op); + gcc_assert (stmt); + + if (NECESSARY (stmt) + || IS_EMPTY_STMT (stmt) + || (phionly && TREE_CODE (stmt) != PHI_NODE)) + return; + + NECESSARY (stmt) = 1; + VEC_safe_push (tree, heap, worklist, stmt); +} + + +/* Mark STMT as necessary if it obviously is. Add it to the worklist if + it can make other statements necessary. + + If AGGRESSIVE is false, control statements are conservatively marked as + necessary. */ + +static void +mark_stmt_if_obviously_necessary (tree stmt, bool aggressive) +{ + stmt_ann_t ann; + tree op; + + /* With non-call exceptions, we have to assume that all statements could + throw. If a statement may throw, it is inherently necessary. */ + if (flag_non_call_exceptions + && tree_could_throw_p (stmt)) + { + mark_stmt_necessary (stmt, true); + return; + } + + /* Statements that are implicitly live. Most function calls, asm and return + statements are required. Labels and BIND_EXPR nodes are kept because + they are control flow, and we have no way of knowing whether they can be + removed. DCE can eliminate all the other statements in a block, and CFG + can then remove the block and labels. */ + switch (TREE_CODE (stmt)) + { + case BIND_EXPR: + case LABEL_EXPR: + case CASE_LABEL_EXPR: + mark_stmt_necessary (stmt, false); + return; + + case ASM_EXPR: + case RESX_EXPR: + case RETURN_EXPR: + mark_stmt_necessary (stmt, true); + return; + + case CALL_EXPR: + /* Most, but not all function calls are required. Function calls that + produce no result and have no side effects (i.e. const pure + functions) are unnecessary. */ + if (TREE_SIDE_EFFECTS (stmt)) + mark_stmt_necessary (stmt, true); + return; + + case MODIFY_EXPR: + op = get_call_expr_in (stmt); + if (op && TREE_SIDE_EFFECTS (op)) + { + mark_stmt_necessary (stmt, true); + return; + } + + /* These values are mildly magic bits of the EH runtime. We can't + see the entire lifetime of these values until landing pads are + generated. */ + if (TREE_CODE (TREE_OPERAND (stmt, 0)) == EXC_PTR_EXPR + || TREE_CODE (TREE_OPERAND (stmt, 0)) == FILTER_EXPR) + { + mark_stmt_necessary (stmt, true); + return; + } + break; + + case GOTO_EXPR: + gcc_assert (!simple_goto_p (stmt)); + mark_stmt_necessary (stmt, true); + return; + + case COND_EXPR: + gcc_assert (EDGE_COUNT (bb_for_stmt (stmt)->succs) == 2); + /* Fall through. */ + + case SWITCH_EXPR: + if (! aggressive) + mark_stmt_necessary (stmt, true); + break; + + default: + break; + } + + ann = stmt_ann (stmt); + + /* If the statement has volatile operands, it needs to be preserved. + Same for statements that can alter control flow in unpredictable + ways. */ + if (ann->has_volatile_ops || is_ctrl_altering_stmt (stmt)) + { + mark_stmt_necessary (stmt, true); + return; + } + + if (is_hidden_global_store (stmt)) + { + mark_stmt_necessary (stmt, true); + return; + } + + return; +} + +/* Find obviously necessary statements. These are things like most function + calls, and stores to file level variables. + + If EL is NULL, control statements are conservatively marked as + necessary. Otherwise it contains the list of edges used by control + dependence analysis. */ + +static void +find_obviously_necessary_stmts (struct edge_list *el) +{ + basic_block bb; + block_stmt_iterator i; + edge e; + + FOR_EACH_BB (bb) + { + tree phi; + + /* Check any PHI nodes in the block. */ + for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) + { + NECESSARY (phi) = 0; + + /* PHIs for virtual variables do not directly affect code + generation and need not be considered inherently necessary + regardless of the bits set in their decl. + + Thus, we only need to mark PHIs for real variables which + need their result preserved as being inherently necessary. */ + if (is_gimple_reg (PHI_RESULT (phi)) + && is_global_var (SSA_NAME_VAR (PHI_RESULT (phi)))) + mark_stmt_necessary (phi, true); + } + + /* Check all statements in the block. */ + for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i)) + { + tree stmt = bsi_stmt (i); + NECESSARY (stmt) = 0; + mark_stmt_if_obviously_necessary (stmt, el != NULL); + } + } + + if (el) + { + /* Prevent the loops from being removed. We must keep the infinite loops, + and we currently do not have a means to recognize the finite ones. */ + FOR_EACH_BB (bb) + { + edge_iterator ei; + FOR_EACH_EDGE (e, ei, bb->succs) + if (e->flags & EDGE_DFS_BACK) + mark_control_dependent_edges_necessary (e->dest, el); + } + } +} + +/* Make corresponding control dependent edges necessary. We only + have to do this once for each basic block, so we clear the bitmap + after we're done. */ +static void +mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el) +{ + bitmap_iterator bi; + unsigned edge_number; + + gcc_assert (bb != EXIT_BLOCK_PTR); + + if (bb == ENTRY_BLOCK_PTR) + return; + + EXECUTE_IF_CONTROL_DEPENDENT (bi, bb->index, edge_number) + { + tree t; + basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number); + + if (TEST_BIT (last_stmt_necessary, cd_bb->index)) + continue; + SET_BIT (last_stmt_necessary, cd_bb->index); + + t = last_stmt (cd_bb); + if (t && is_ctrl_stmt (t)) + mark_stmt_necessary (t, true); + } +} + +/* Propagate necessity using the operands of necessary statements. Process + the uses on each statement in the worklist, and add all feeding statements + which contribute to the calculation of this value to the worklist. + + In conservative mode, EL is NULL. */ + +static void +propagate_necessity (struct edge_list *el) +{ + tree i; + bool aggressive = (el ? true : false); + + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "\nProcessing worklist:\n"); + + while (VEC_length (tree, worklist) > 0) + { + /* Take `i' from worklist. */ + i = VEC_pop (tree, worklist); + + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, "processing: "); + print_generic_stmt (dump_file, i, TDF_SLIM); + fprintf (dump_file, "\n"); + } + + if (aggressive) + { + /* Mark the last statements of the basic blocks that the block + containing `i' is control dependent on, but only if we haven't + already done so. */ + basic_block bb = bb_for_stmt (i); + if (bb != ENTRY_BLOCK_PTR + && ! TEST_BIT (visited_control_parents, bb->index)) + { + SET_BIT (visited_control_parents, bb->index); + mark_control_dependent_edges_necessary (bb, el); + } + } + + if (TREE_CODE (i) == PHI_NODE) + { + /* PHI nodes are somewhat special in that each PHI alternative has + data and control dependencies. All the statements feeding the + PHI node's arguments are always necessary. In aggressive mode, + we also consider the control dependent edges leading to the + predecessor block associated with each PHI alternative as + necessary. */ + int k; + for (k = 0; k < PHI_NUM_ARGS (i); k++) + { + tree arg = PHI_ARG_DEF (i, k); + if (TREE_CODE (arg) == SSA_NAME) + mark_operand_necessary (arg, false); + } + + if (aggressive) + { + for (k = 0; k < PHI_NUM_ARGS (i); k++) + { + basic_block arg_bb = PHI_ARG_EDGE (i, k)->src; + if (arg_bb != ENTRY_BLOCK_PTR + && ! TEST_BIT (visited_control_parents, arg_bb->index)) + { + SET_BIT (visited_control_parents, arg_bb->index); + mark_control_dependent_edges_necessary (arg_bb, el); + } + } + } + } + else + { + /* Propagate through the operands. Examine all the USE, VUSE and + V_MAY_DEF operands in this statement. Mark all the statements + which feed this statement's uses as necessary. */ + ssa_op_iter iter; + tree use; + + /* The operands of V_MAY_DEF expressions are also needed as they + represent potential definitions that may reach this + statement (V_MAY_DEF operands allow us to follow def-def + links). */ + + FOR_EACH_SSA_TREE_OPERAND (use, i, iter, SSA_OP_ALL_USES) + mark_operand_necessary (use, false); + } + } +} + + +/* Propagate necessity around virtual phi nodes used in kill operands. + The reason this isn't done during propagate_necessity is because we don't + want to keep phis around that are just there for must-defs, unless we + absolutely have to. After we've rewritten the reaching definitions to be + correct in the previous part of the fixup routine, we can simply propagate + around the information about which of these virtual phi nodes are really + used, and set the NECESSARY flag accordingly. + Note that we do the minimum here to ensure that we keep alive the phis that + are actually used in the corrected SSA form. In particular, some of these + phis may now have all of the same operand, and will be deleted by some + other pass. */ + +static void +mark_really_necessary_kill_operand_phis (void) +{ + basic_block bb; + int i; + + /* Seed the worklist with the new virtual phi arguments and virtual + uses */ + FOR_EACH_BB (bb) + { + block_stmt_iterator bsi; + tree phi; + + for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) + { + if (!is_gimple_reg (PHI_RESULT (phi)) && NECESSARY (phi)) + { + for (i = 0; i < PHI_NUM_ARGS (phi); i++) + mark_operand_necessary (PHI_ARG_DEF (phi, i), true); + } + } + + for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi)) + { + tree stmt = bsi_stmt (bsi); + + if (NECESSARY (stmt)) + { + use_operand_p use_p; + ssa_op_iter iter; + FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, + SSA_OP_VIRTUAL_USES | SSA_OP_VIRTUAL_KILLS) + { + tree use = USE_FROM_PTR (use_p); + mark_operand_necessary (use, true); + } + } + } + } + + /* Mark all virtual phis still in use as necessary, and all of their + arguments that are phis as necessary. */ + while (VEC_length (tree, worklist) > 0) + { + tree use = VEC_pop (tree, worklist); + + for (i = 0; i < PHI_NUM_ARGS (use); i++) + mark_operand_necessary (PHI_ARG_DEF (use, i), true); + } +} + + + + +/* Eliminate unnecessary statements. Any instruction not marked as necessary + contributes nothing to the program, and can be deleted. */ + +static void +eliminate_unnecessary_stmts (void) +{ + basic_block bb; + block_stmt_iterator i; + + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "\nEliminating unnecessary statements:\n"); + + clear_special_calls (); + FOR_EACH_BB (bb) + { + /* Remove dead PHI nodes. */ + remove_dead_phis (bb); + } + + FOR_EACH_BB (bb) + { + /* Remove dead statements. */ + for (i = bsi_start (bb); ! bsi_end_p (i) ; ) + { + tree t = bsi_stmt (i); + + stats.total++; + + /* If `i' is not necessary then remove it. */ + if (! NECESSARY (t)) + remove_dead_stmt (&i, bb); + else + { + tree call = get_call_expr_in (t); + if (call) + notice_special_calls (call); + bsi_next (&i); + } + } + } + } + +/* Remove dead PHI nodes from block BB. */ + +static void +remove_dead_phis (basic_block bb) +{ + tree prev, phi; + + prev = NULL_TREE; + phi = phi_nodes (bb); + while (phi) + { + stats.total_phis++; + + if (! NECESSARY (phi)) + { + tree next = PHI_CHAIN (phi); + + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, "Deleting : "); + print_generic_stmt (dump_file, phi, TDF_SLIM); + fprintf (dump_file, "\n"); + } + + remove_phi_node (phi, prev); + stats.removed_phis++; + phi = next; + } + else + { + prev = phi; + phi = PHI_CHAIN (phi); + } + } +} + +/* Remove dead statement pointed to by iterator I. Receives the basic block BB + containing I so that we don't have to look it up. */ + +static void +remove_dead_stmt (block_stmt_iterator *i, basic_block bb) +{ + tree t = bsi_stmt (*i); + def_operand_p def_p; + + ssa_op_iter iter; + + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, "Deleting : "); + print_generic_stmt (dump_file, t, TDF_SLIM); + fprintf (dump_file, "\n"); + } + + stats.removed++; + + /* If we have determined that a conditional branch statement contributes + nothing to the program, then we not only remove it, but we also change + the flow graph so that the current block will simply fall-thru to its + immediate post-dominator. The blocks we are circumventing will be + removed by cleanup_tree_cfg if this change in the flow graph makes them + unreachable. */ + if (is_ctrl_stmt (t)) + { + basic_block post_dom_bb; + + /* The post dominance info has to be up-to-date. */ + gcc_assert (dom_computed[CDI_POST_DOMINATORS] == DOM_OK); + /* Get the immediate post dominator of bb. */ + post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb); + + /* There are three particularly problematical cases. + + 1. Blocks that do not have an immediate post dominator. This + can happen with infinite loops. + + 2. Blocks that are only post dominated by the exit block. These + can also happen for infinite loops as we create fake edges + in the dominator tree. + + 3. If the post dominator has PHI nodes we may be able to compute + the right PHI args for them. + + + In each of these cases we must remove the control statement + as it may reference SSA_NAMEs which are going to be removed and + we remove all but one outgoing edge from the block. */ + if (! post_dom_bb + || post_dom_bb == EXIT_BLOCK_PTR + || phi_nodes (post_dom_bb)) + ; + else + { + /* Redirect the first edge out of BB to reach POST_DOM_BB. */ + redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb); + PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL; + } + EDGE_SUCC (bb, 0)->probability = REG_BR_PROB_BASE; + EDGE_SUCC (bb, 0)->count = bb->count; + + /* The edge is no longer associated with a conditional, so it does + not have TRUE/FALSE flags. */ + EDGE_SUCC (bb, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE); + + /* The lone outgoing edge from BB will be a fallthru edge. */ + EDGE_SUCC (bb, 0)->flags |= EDGE_FALLTHRU; + + /* Remove the remaining the outgoing edges. */ + while (!single_succ_p (bb)) + { + /* FIXME. When we remove the edge, we modify the CFG, which + in turn modifies the dominator and post-dominator tree. + Is it safe to postpone recomputing the dominator and + post-dominator tree until the end of this pass given that + the post-dominators are used above? */ + cfg_altered = true; + remove_edge (EDGE_SUCC (bb, 1)); + } + } + + FOR_EACH_SSA_DEF_OPERAND (def_p, t, iter, SSA_OP_VIRTUAL_DEFS) + { + tree def = DEF_FROM_PTR (def_p); + mark_sym_for_renaming (SSA_NAME_VAR (def)); + } + bsi_remove (i, true); + release_defs (t); +} + +/* Print out removed statement statistics. */ + +static void +print_stats (void) +{ + if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS))) + { + float percg; + + percg = ((float) stats.removed / (float) stats.total) * 100; + fprintf (dump_file, "Removed %d of %d statements (%d%%)\n", + stats.removed, stats.total, (int) percg); + + if (stats.total_phis == 0) + percg = 0; + else + percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100; + + fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n", + stats.removed_phis, stats.total_phis, (int) percg); + } +} + +/* Initialization for this pass. Set up the used data structures. */ + +static void +tree_dce_init (bool aggressive) +{ + memset ((void *) &stats, 0, sizeof (stats)); + + if (aggressive) + { + int i; + + control_dependence_map = XNEWVEC (bitmap, last_basic_block); + for (i = 0; i < last_basic_block; ++i) + control_dependence_map[i] = BITMAP_ALLOC (NULL); + + last_stmt_necessary = sbitmap_alloc (last_basic_block); + sbitmap_zero (last_stmt_necessary); + } + + processed = sbitmap_alloc (num_ssa_names + 1); + sbitmap_zero (processed); + + worklist = VEC_alloc (tree, heap, 64); + cfg_altered = false; +} + +/* Cleanup after this pass. */ + +static void +tree_dce_done (bool aggressive) +{ + if (aggressive) + { + int i; + + for (i = 0; i < last_basic_block; ++i) + BITMAP_FREE (control_dependence_map[i]); + free (control_dependence_map); + + sbitmap_free (visited_control_parents); + sbitmap_free (last_stmt_necessary); + } + + sbitmap_free (processed); + + VEC_free (tree, heap, worklist); +} + +/* Main routine to eliminate dead code. + + AGGRESSIVE controls the aggressiveness of the algorithm. + In conservative mode, we ignore control dependence and simply declare + all but the most trivially dead branches necessary. This mode is fast. + In aggressive mode, control dependences are taken into account, which + results in more dead code elimination, but at the cost of some time. + + FIXME: Aggressive mode before PRE doesn't work currently because + the dominance info is not invalidated after DCE1. This is + not an issue right now because we only run aggressive DCE + as the last tree SSA pass, but keep this in mind when you + start experimenting with pass ordering. */ + +static void +perform_tree_ssa_dce (bool aggressive) +{ + struct edge_list *el = NULL; + + tree_dce_init (aggressive); + + if (aggressive) + { + /* Compute control dependence. */ + timevar_push (TV_CONTROL_DEPENDENCES); + calculate_dominance_info (CDI_POST_DOMINATORS); + el = create_edge_list (); + find_all_control_dependences (el); + timevar_pop (TV_CONTROL_DEPENDENCES); + + visited_control_parents = sbitmap_alloc (last_basic_block); + sbitmap_zero (visited_control_parents); + + mark_dfs_back_edges (); + } + + find_obviously_necessary_stmts (el); + + propagate_necessity (el); + + mark_really_necessary_kill_operand_phis (); + eliminate_unnecessary_stmts (); + + if (aggressive) + free_dominance_info (CDI_POST_DOMINATORS); + + /* If we removed paths in the CFG, then we need to update + dominators as well. I haven't investigated the possibility + of incrementally updating dominators. */ + if (cfg_altered) + free_dominance_info (CDI_DOMINATORS); + + /* Debugging dumps. */ + if (dump_file) + print_stats (); + + tree_dce_done (aggressive); + + free_edge_list (el); +} + +/* Pass entry points. */ +static unsigned int +tree_ssa_dce (void) +{ + perform_tree_ssa_dce (/*aggressive=*/false); + return 0; +} + +static unsigned int +tree_ssa_dce_loop (void) +{ + perform_tree_ssa_dce (/*aggressive=*/false); + free_numbers_of_iterations_estimates (current_loops); + scev_reset (); + return 0; +} + +static unsigned int +tree_ssa_cd_dce (void) +{ + perform_tree_ssa_dce (/*aggressive=*/optimize >= 2); + return 0; +} + +static bool +gate_dce (void) +{ + return flag_tree_dce != 0; +} + +struct tree_opt_pass pass_dce = +{ + "dce", /* name */ + gate_dce, /* gate */ + tree_ssa_dce, /* execute */ + NULL, /* sub */ + NULL, /* next */ + 0, /* static_pass_number */ + TV_TREE_DCE, /* 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_ggc_collect + | TODO_verify_ssa + | TODO_remove_unused_locals, /* todo_flags_finish */ + 0 /* letter */ +}; + +struct tree_opt_pass pass_dce_loop = +{ + "dceloop", /* name */ + gate_dce, /* gate */ + tree_ssa_dce_loop, /* execute */ + NULL, /* sub */ + NULL, /* next */ + 0, /* static_pass_number */ + TV_TREE_DCE, /* 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 */ +}; + +struct tree_opt_pass pass_cd_dce = +{ + "cddce", /* name */ + gate_dce, /* gate */ + tree_ssa_cd_dce, /* execute */ + NULL, /* sub */ + NULL, /* next */ + 0, /* static_pass_number */ + TV_TREE_CD_DCE, /* 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_ggc_collect + | TODO_verify_ssa + | TODO_verify_flow, /* todo_flags_finish */ + 0 /* letter */ +}; |
