/* Dead code elimination pass for the GNU compiler. Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc. Contributed by Ben Elliston and Andrew MacLeod 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 3, 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 COPYING3. If not see . */ /* 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 "gimple.h" #include "tree-dump.h" #include "tree-pass.h" #include "timevar.h" #include "flags.h" #include "cfgloop.h" #include "tree-scalar-evolution.h" #include "pointer-set.h" #include "langhooks.h" static struct stmt_stats { int total; int total_phis; int removed; int removed_phis; } stats; #define STMT_NECESSARY GF_PLF_1 DEF_VEC_P(use_operand_p); DEF_VEC_ALLOC_P(use_operand_p, heap); static VEC(gimple,heap) *worklist; /* Vector indicating an SSA name has already been processed and marked as necessary. */ static sbitmap processed; /* Pointer set of stmt killed by delete. */ static struct pointer_set_t *killed_by_delete; /* 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)) /* 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]); } /* 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; } } /* 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); } } /* 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); } /* 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 (gimple stmt, bool add_to_worklist) { gcc_assert (stmt); if (gimple_plf (stmt, STMT_NECESSARY)) return; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Marking useful stmt: "); print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); fprintf (dump_file, "\n"); } gimple_set_plf (stmt, STMT_NECESSARY, true); if (add_to_worklist) VEC_safe_push (gimple, heap, worklist, stmt); } /* Follow the UD chain to find the base pointer for pointer PTR. */ static tree find_base_ptr (tree ptr) { STRIP_NOPS (ptr); if (TREE_CODE (ptr) != SSA_NAME) return ptr; do { gimple stmt = SSA_NAME_DEF_STMT (ptr); if (!stmt || gimple_code (stmt) != GIMPLE_ASSIGN) return ptr; if (gimple_assign_copy_p (stmt) || gimple_assign_unary_nop_p (stmt) || gimple_assign_rhs_code (stmt) == POINTER_PLUS_EXPR) { tree rhs = gimple_assign_rhs1 (stmt); STRIP_NOPS (rhs); if (TREE_CODE (rhs) != SSA_NAME) return ptr; else ptr = rhs; } else return ptr; } while (true); return ptr; } /* Returns true if the STMT's def is used by a global delete call and there is no real uses of the definition by the intervening stmts. */ static bool is_killed_by_delete (gimple stmt) { tree lhs, base, base_ptr; gimple use_stmt, delete_stmt = NULL; struct voptype_d *vdefs; use_operand_p use_op; imm_use_iterator iter; if (pointer_set_contains (killed_by_delete, stmt)) return true; lhs = gimple_assign_lhs (stmt); base = get_base_address (lhs); if (TREE_CODE (base) != INDIRECT_REF) return false; base_ptr = TREE_OPERAND (base, 0); base_ptr = find_base_ptr (base_ptr); vdefs = gimple_vdef_ops (stmt); while (vdefs) { FOR_EACH_IMM_USE_FAST (use_op, iter, VDEF_RESULT (vdefs)) { use_stmt = USE_STMT (use_op); if (is_global_delete_call (use_stmt)) { tree arg = gimple_call_arg (use_stmt, 0); arg = find_base_ptr (arg); if (base_ptr == arg) { delete_stmt = use_stmt; break; } } } if (delete_stmt) break; vdefs = vdefs->next; } if (!delete_stmt) return false; /* Ideally we should check if DELETE_STMT post dominate stmt, but post dominance information is not guaranteed to exist, so we just check if they are in the same BB of if BB of delete is the single successor of vptr init stmt's BB. */ if (gimple_bb (delete_stmt) != gimple_bb (stmt) && !(single_succ_p (gimple_bb (stmt)) && single_succ (gimple_bb (stmt)) == gimple_bb (delete_stmt))) return false; /* Now check if all other use stmts are dominated by DELETE_STMT. */ vdefs = gimple_vdef_ops (stmt); while (vdefs) { FOR_EACH_IMM_USE_FAST (use_op, iter, VDEF_RESULT (vdefs)) { use_stmt = USE_STMT (use_op); if (use_stmt != delete_stmt && !stmt_dominates_stmt_p (delete_stmt, use_stmt)) return false; } vdefs = vdefs->next; } pointer_set_insert (killed_by_delete, stmt); return true; } /* Mark the statement defining operand OP as necessary. */ static inline void mark_operand_necessary (tree op) { gimple 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); if (!stmt || gimple_plf (stmt, STMT_NECESSARY) || gimple_nop_p (stmt)) return; if (is_vptr_init (stmt) && is_killed_by_delete (stmt)) { /* Do not mark STMT as necessary, but put it in worklist. This allows uses to propagate up via Def-Def chain. */ VEC_safe_push (gimple, heap, worklist, stmt); return; } gimple_set_plf (stmt, STMT_NECESSARY, true); VEC_safe_push (gimple, 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 (gimple stmt, bool aggressive) { tree lhs = NULL_TREE; /* 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 && stmt_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 GIMPLE_BIND 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 (gimple_code (stmt)) { case GIMPLE_PREDICT: case GIMPLE_LABEL: mark_stmt_necessary (stmt, false); return; case GIMPLE_ASM: case GIMPLE_RESX: case GIMPLE_RETURN: case GIMPLE_CHANGE_DYNAMIC_TYPE: mark_stmt_necessary (stmt, true); return; case GIMPLE_CALL: /* 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 (gimple_has_side_effects (stmt)) { mark_stmt_necessary (stmt, true); return; } if (!gimple_call_lhs (stmt)) return; lhs = gimple_call_lhs (stmt); /* Fall through */ case GIMPLE_ASSIGN: if (!lhs) lhs = gimple_assign_lhs (stmt); /* 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 (lhs) == EXC_PTR_EXPR || TREE_CODE (lhs) == FILTER_EXPR) { mark_stmt_necessary (stmt, true); return; } break; case GIMPLE_GOTO: gcc_assert (!simple_goto_p (stmt)); mark_stmt_necessary (stmt, true); return; case GIMPLE_COND: gcc_assert (EDGE_COUNT (gimple_bb (stmt)->succs) == 2); /* Fall through. */ case GIMPLE_SWITCH: if (! aggressive) mark_stmt_necessary (stmt, true); break; default: break; } /* If the statement has volatile operands, it needs to be preserved. Same for statements that can alter control flow in unpredictable ways. */ if (gimple_has_volatile_ops (stmt) || is_ctrl_altering_stmt (stmt)) { mark_stmt_necessary (stmt, true); return; } if (is_vptr_init (stmt)) { /* Initialization of the vptr field for the same object this destructor is operating on won't be live out of the function if it is not used within the function, so do not treat them as a hidden global store. */ if (lang_hooks.decls.is_decl_dtor (current_function_decl)) { tree base, base_ptr; tree lhs = gimple_assign_lhs (stmt); base = get_base_address (lhs); if (TREE_CODE (base) == INDIRECT_REF) { base_ptr = TREE_OPERAND (base, 0); base_ptr = find_base_ptr (base_ptr); if ((TREE_CODE (base_ptr) == SSA_NAME) && (gimple_nop_p (SSA_NAME_DEF_STMT (base_ptr)))) return; } } if (is_killed_by_delete (stmt)) return; } if (is_hidden_global_store (stmt)) { mark_stmt_necessary (stmt, true); return; } return; } /* 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) { gimple stmt; 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); stmt = last_stmt (cd_bb); if (stmt && is_ctrl_stmt (stmt)) mark_stmt_necessary (stmt, true); } } /* 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; gimple_stmt_iterator gsi; edge e; gimple phi, stmt; FOR_EACH_BB (bb) { /* PHI nodes are never inherently necessary. */ for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { phi = gsi_stmt (gsi); gimple_set_plf (phi, STMT_NECESSARY, false); } /* Check all statements in the block. */ for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { stmt = gsi_stmt (gsi); gimple_set_plf (stmt, STMT_NECESSARY, false); 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); } } } /* 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) { gimple stmt; bool aggressive = (el ? true : false); if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, "\nProcessing worklist:\n"); while (VEC_length (gimple, worklist) > 0) { /* Take STMT from worklist. */ stmt = VEC_pop (gimple, worklist); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "processing: "); print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); fprintf (dump_file, "\n"); } if (aggressive) { /* Mark the last statements of the basic blocks that the block containing STMT is control dependent on, but only if we haven't already done so. */ basic_block bb = gimple_bb (stmt); 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 (gimple_code (stmt) == GIMPLE_PHI) { /* 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. */ size_t k; for (k = 0; k < gimple_phi_num_args (stmt); k++) { tree arg = PHI_ARG_DEF (stmt, k); if (TREE_CODE (arg) == SSA_NAME) mark_operand_necessary (arg); } if (aggressive) { for (k = 0; k < gimple_phi_num_args (stmt); k++) { basic_block arg_bb = gimple_phi_arg_edge (stmt, 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 VDEF operands in this statement. Mark all the statements which feed this statement's uses as necessary. The operands of VDEF expressions are also needed as they represent potential definitions that may reach this statement (VDEF operands allow us to follow def-def links). */ ssa_op_iter iter; tree use; int use_flags = SSA_OP_ALL_USES; /* Special case of dead vptr initialization followed by operator delete -- non virtual uses do not need to be propagated, but only virtual uses which link up def-def chains. */ if (!gimple_plf (stmt, STMT_NECESSARY)) use_flags = SSA_OP_VIRTUAL_USES; FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, use_flags) mark_operand_necessary (use); } } } /* Remove dead PHI nodes from block BB. */ static bool remove_dead_phis (basic_block bb) { bool something_changed = false; gimple_seq phis; gimple phi; gimple_stmt_iterator gsi; phis = phi_nodes (bb); for (gsi = gsi_start (phis); !gsi_end_p (gsi);) { stats.total_phis++; phi = gsi_stmt (gsi); if (!gimple_plf (phi, STMT_NECESSARY)) { something_changed = true; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Deleting : "); print_gimple_stmt (dump_file, phi, 0, TDF_SLIM); fprintf (dump_file, "\n"); } remove_phi_node (&gsi, true); stats.removed_phis++; } else { gsi_next (&gsi); } } return something_changed; } /* Fix up references to VOP SSANAMEs defined by STMT which is to be removed. */ static void fixup_vdef_refs (gimple stmt) { struct voptype_d *vdefs; use_operand_p use_op; imm_use_iterator iter; vdefs = gimple_vdef_ops (stmt); while (vdefs) { int n, j; tree prev_nm; VEC(use_operand_p, heap) *fixup_opnds = NULL; n = VDEF_NUM (vdefs); gcc_assert (n == 1); prev_nm = VDEF_OP (vdefs, 0); FOR_EACH_IMM_USE_FAST (use_op, iter, VDEF_RESULT (vdefs)) VEC_safe_push (use_operand_p, heap, fixup_opnds, use_op); for (j = 0; VEC_iterate (use_operand_p, fixup_opnds, j, use_op); ++j) set_ssa_use_from_ptr (use_op, prev_nm); vdefs = vdefs->next; } } /* 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 (gimple_stmt_iterator *i, basic_block bb) { gimple stmt = gsi_stmt (*i); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Deleting : "); print_gimple_stmt (dump_file, stmt, 0, 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 (stmt)) { basic_block post_dom_bb; /* The post dominance info has to be up-to-date. */ gcc_assert (dom_info_state (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; /* It is not sufficient to set cfg_altered below during edge removal, in case BB has two successors and one of them is POST_DOM_BB. */ cfg_altered = true; } 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)); } } /* Due to imprecise def-use information, the deleted vptr init assignment have uses, which need to be fixed to previous versions of the virtual ops defined by STMT. */ if (is_vptr_init (stmt) && is_killed_by_delete (stmt)) { gimple_stmt_iterator gsi; gimple next_stmt; gsi = gsi_for_stmt (stmt); gsi_next (&gsi); if (!gsi_end_p (gsi)) next_stmt = gsi_stmt (gsi); else { basic_block nbb; gcc_assert (single_succ_p (gimple_bb (stmt))); nbb = single_succ (gimple_bb (stmt)); gsi = gsi_after_labels (nbb); gcc_assert (!gsi_end_p (gsi)); next_stmt = gsi_stmt (gsi); } /* Now fixup SSA. */ fixup_vdef_refs (stmt); } gsi_remove (i, true); release_defs (stmt); } /* Eliminate unnecessary statements. Any instruction not marked as necessary contributes nothing to the program, and can be deleted. */ static bool eliminate_unnecessary_stmts (void) { bool something_changed = false; basic_block bb; gimple_stmt_iterator gsi; gimple stmt; tree call; 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. */ something_changed |= remove_dead_phis (bb); } FOR_EACH_BB (bb) { /* Remove dead statements. */ for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi);) { stmt = gsi_stmt (gsi); stats.total++; /* If GSI is not necessary then remove it. */ if (!gimple_plf (stmt, STMT_NECESSARY)) { remove_dead_stmt (&gsi, bb); something_changed = true; } else if (is_gimple_call (stmt)) { call = gimple_call_fndecl (stmt); if (call) { tree name; gimple g; /* When LHS of var = call (); is dead, simplify it into call (); saving one operand. */ name = gimple_call_lhs (stmt); if (name && TREE_CODE (name) == SSA_NAME && !TEST_BIT (processed, SSA_NAME_VERSION (name))) { something_changed = true; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Deleting LHS of call: "); print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); fprintf (dump_file, "\n"); } push_stmt_changes (gsi_stmt_ptr (&gsi)); g = gimple_copy (stmt); gimple_call_set_lhs (g, NULL_TREE); gsi_replace (&gsi, g, false); maybe_clean_or_replace_eh_stmt (stmt, g); mark_symbols_for_renaming (g); pop_stmt_changes (gsi_stmt_ptr (&gsi)); release_ssa_name (name); } notice_special_calls (stmt); } gsi_next (&gsi); } else { gsi_next (&gsi); } } } return something_changed; } /* Print out removed statement statistics. */ static void print_stats (void) { 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); killed_by_delete = pointer_set_create (); worklist = VEC_alloc (gimple, 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); pointer_set_destroy (killed_by_delete); VEC_free (gimple, 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 unsigned int perform_tree_ssa_dce (bool aggressive) { struct edge_list *el = NULL; bool something_changed = 0; 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); something_changed |= eliminate_unnecessary_stmts (); something_changed |= cfg_altered; /* We do not update postdominators, so free them unconditionally. */ 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); statistics_counter_event (cfun, "Statements deleted", stats.removed); statistics_counter_event (cfun, "PHI nodes deleted", stats.removed_phis); /* Debugging dumps. */ if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS))) print_stats (); tree_dce_done (aggressive); free_edge_list (el); if (something_changed) return (TODO_update_ssa | TODO_cleanup_cfg | TODO_ggc_collect | TODO_remove_unused_locals); else return 0; } /* Pass entry points. */ static unsigned int tree_ssa_dce (void) { return perform_tree_ssa_dce (/*aggressive=*/false); } static unsigned int tree_ssa_dce_loop (void) { unsigned int todo; todo = perform_tree_ssa_dce (/*aggressive=*/false); if (todo) { free_numbers_of_iterations_estimates (); scev_reset (); } return todo; } static unsigned int tree_ssa_cd_dce (void) { return perform_tree_ssa_dce (/*aggressive=*/optimize >= 2); } static bool gate_dce (void) { return flag_tree_dce != 0; } struct gimple_opt_pass pass_dce = { { GIMPLE_PASS, "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, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */ } }; struct gimple_opt_pass pass_dce_loop = { { GIMPLE_PASS, "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, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */ } }; struct gimple_opt_pass pass_cd_dce = { { GIMPLE_PASS, "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, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_verify_ssa | TODO_verify_flow /* todo_flags_finish */ } };