963 lines
26 KiB
C
963 lines
26 KiB
C
/* Dead code elimination pass for the GNU compiler.
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Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008
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Free Software Foundation, Inc.
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Contributed by Ben Elliston <bje@redhat.com>
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and Andrew MacLeod <amacleod@redhat.com>
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Adapted to use control dependence by Steven Bosscher, SUSE Labs.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 3, or (at your option) any
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later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3. If not see
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<http://www.gnu.org/licenses/>. */
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/* Dead code elimination.
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References:
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Building an Optimizing Compiler,
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Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
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Advanced Compiler Design and Implementation,
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Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10.
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Dead-code elimination is the removal of statements which have no
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impact on the program's output. "Dead statements" have no impact
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on the program's output, while "necessary statements" may have
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impact on the output.
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The algorithm consists of three phases:
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1. Marking as necessary all statements known to be necessary,
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e.g. most function calls, writing a value to memory, etc;
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2. Propagating necessary statements, e.g., the statements
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giving values to operands in necessary statements; and
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3. Removing dead statements. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "tm.h"
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#include "ggc.h"
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/* These RTL headers are needed for basic-block.h. */
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#include "rtl.h"
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#include "tm_p.h"
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#include "hard-reg-set.h"
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#include "obstack.h"
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#include "basic-block.h"
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#include "tree.h"
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#include "diagnostic.h"
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#include "tree-flow.h"
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#include "gimple.h"
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#include "tree-dump.h"
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#include "tree-pass.h"
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#include "timevar.h"
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#include "flags.h"
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#include "cfgloop.h"
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#include "tree-scalar-evolution.h"
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static struct stmt_stats
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{
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int total;
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int total_phis;
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int removed;
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int removed_phis;
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} stats;
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#define STMT_NECESSARY GF_PLF_1
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static VEC(gimple,heap) *worklist;
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/* Vector indicating an SSA name has already been processed and marked
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as necessary. */
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static sbitmap processed;
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/* Vector indicating that last_stmt if a basic block has already been
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marked as necessary. */
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static sbitmap last_stmt_necessary;
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/* Before we can determine whether a control branch is dead, we need to
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compute which blocks are control dependent on which edges.
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We expect each block to be control dependent on very few edges so we
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use a bitmap for each block recording its edges. An array holds the
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bitmap. The Ith bit in the bitmap is set if that block is dependent
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on the Ith edge. */
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static bitmap *control_dependence_map;
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/* Vector indicating that a basic block has already had all the edges
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processed that it is control dependent on. */
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static sbitmap visited_control_parents;
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/* TRUE if this pass alters the CFG (by removing control statements).
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FALSE otherwise.
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If this pass alters the CFG, then it will arrange for the dominators
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to be recomputed. */
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static bool cfg_altered;
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/* Execute code that follows the macro for each edge (given number
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EDGE_NUMBER within the CODE) for which the block with index N is
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control dependent. */
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#define EXECUTE_IF_CONTROL_DEPENDENT(BI, N, EDGE_NUMBER) \
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EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[(N)], 0, \
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(EDGE_NUMBER), (BI))
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/* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */
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static inline void
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set_control_dependence_map_bit (basic_block bb, int edge_index)
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{
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if (bb == ENTRY_BLOCK_PTR)
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return;
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gcc_assert (bb != EXIT_BLOCK_PTR);
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bitmap_set_bit (control_dependence_map[bb->index], edge_index);
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}
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/* Clear all control dependences for block BB. */
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static inline void
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clear_control_dependence_bitmap (basic_block bb)
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{
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bitmap_clear (control_dependence_map[bb->index]);
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}
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/* Find the immediate postdominator PDOM of the specified basic block BLOCK.
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This function is necessary because some blocks have negative numbers. */
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static inline basic_block
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find_pdom (basic_block block)
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{
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gcc_assert (block != ENTRY_BLOCK_PTR);
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if (block == EXIT_BLOCK_PTR)
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return EXIT_BLOCK_PTR;
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else
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{
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basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block);
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if (! bb)
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return EXIT_BLOCK_PTR;
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return bb;
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}
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}
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/* Determine all blocks' control dependences on the given edge with edge_list
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EL index EDGE_INDEX, ala Morgan, Section 3.6. */
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static void
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find_control_dependence (struct edge_list *el, int edge_index)
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{
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basic_block current_block;
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basic_block ending_block;
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gcc_assert (INDEX_EDGE_PRED_BB (el, edge_index) != EXIT_BLOCK_PTR);
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if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR)
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ending_block = single_succ (ENTRY_BLOCK_PTR);
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else
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ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index));
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for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index);
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current_block != ending_block && current_block != EXIT_BLOCK_PTR;
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current_block = find_pdom (current_block))
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{
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edge e = INDEX_EDGE (el, edge_index);
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/* For abnormal edges, we don't make current_block control
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dependent because instructions that throw are always necessary
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anyway. */
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if (e->flags & EDGE_ABNORMAL)
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continue;
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set_control_dependence_map_bit (current_block, edge_index);
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}
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}
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/* Record all blocks' control dependences on all edges in the edge
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list EL, ala Morgan, Section 3.6. */
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static void
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find_all_control_dependences (struct edge_list *el)
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{
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int i;
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for (i = 0; i < NUM_EDGES (el); ++i)
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find_control_dependence (el, i);
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}
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/* If STMT is not already marked necessary, mark it, and add it to the
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worklist if ADD_TO_WORKLIST is true. */
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static inline void
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mark_stmt_necessary (gimple stmt, bool add_to_worklist)
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{
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gcc_assert (stmt);
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if (gimple_plf (stmt, STMT_NECESSARY))
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return;
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if (dump_file && (dump_flags & TDF_DETAILS))
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{
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fprintf (dump_file, "Marking useful stmt: ");
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print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
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fprintf (dump_file, "\n");
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}
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gimple_set_plf (stmt, STMT_NECESSARY, true);
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if (add_to_worklist)
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VEC_safe_push (gimple, heap, worklist, stmt);
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}
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/* Mark the statement defining operand OP as necessary. */
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static inline void
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mark_operand_necessary (tree op)
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{
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gimple stmt;
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int ver;
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gcc_assert (op);
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ver = SSA_NAME_VERSION (op);
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if (TEST_BIT (processed, ver))
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return;
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SET_BIT (processed, ver);
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stmt = SSA_NAME_DEF_STMT (op);
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gcc_assert (stmt);
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if (gimple_plf (stmt, STMT_NECESSARY) || gimple_nop_p (stmt))
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return;
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gimple_set_plf (stmt, STMT_NECESSARY, true);
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VEC_safe_push (gimple, heap, worklist, stmt);
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}
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/* Mark STMT as necessary if it obviously is. Add it to the worklist if
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it can make other statements necessary.
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If AGGRESSIVE is false, control statements are conservatively marked as
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necessary. */
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static void
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mark_stmt_if_obviously_necessary (gimple stmt, bool aggressive)
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{
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tree lhs = NULL_TREE;
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/* With non-call exceptions, we have to assume that all statements could
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throw. If a statement may throw, it is inherently necessary. */
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if (flag_non_call_exceptions
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&& stmt_could_throw_p (stmt))
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{
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mark_stmt_necessary (stmt, true);
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return;
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}
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/* Statements that are implicitly live. Most function calls, asm
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and return statements are required. Labels and GIMPLE_BIND nodes
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are kept because they are control flow, and we have no way of
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knowing whether they can be removed. DCE can eliminate all the
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other statements in a block, and CFG can then remove the block
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and labels. */
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switch (gimple_code (stmt))
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{
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case GIMPLE_PREDICT:
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case GIMPLE_LABEL:
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mark_stmt_necessary (stmt, false);
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return;
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case GIMPLE_ASM:
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case GIMPLE_RESX:
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case GIMPLE_RETURN:
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case GIMPLE_CHANGE_DYNAMIC_TYPE:
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mark_stmt_necessary (stmt, true);
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return;
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case GIMPLE_CALL:
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/* Most, but not all function calls are required. Function calls that
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produce no result and have no side effects (i.e. const pure
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functions) are unnecessary. */
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if (gimple_has_side_effects (stmt))
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{
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mark_stmt_necessary (stmt, true);
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return;
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}
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if (!gimple_call_lhs (stmt))
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return;
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lhs = gimple_call_lhs (stmt);
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/* Fall through */
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case GIMPLE_ASSIGN:
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if (!lhs)
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lhs = gimple_assign_lhs (stmt);
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/* These values are mildly magic bits of the EH runtime. We can't
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see the entire lifetime of these values until landing pads are
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generated. */
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if (TREE_CODE (lhs) == EXC_PTR_EXPR
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|| TREE_CODE (lhs) == FILTER_EXPR)
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{
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mark_stmt_necessary (stmt, true);
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return;
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}
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break;
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case GIMPLE_GOTO:
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gcc_assert (!simple_goto_p (stmt));
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mark_stmt_necessary (stmt, true);
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return;
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case GIMPLE_COND:
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gcc_assert (EDGE_COUNT (gimple_bb (stmt)->succs) == 2);
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/* Fall through. */
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case GIMPLE_SWITCH:
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if (! aggressive)
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mark_stmt_necessary (stmt, true);
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break;
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default:
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break;
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}
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/* If the statement has volatile operands, it needs to be preserved.
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Same for statements that can alter control flow in unpredictable
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ways. */
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if (gimple_has_volatile_ops (stmt) || is_ctrl_altering_stmt (stmt))
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{
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mark_stmt_necessary (stmt, true);
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return;
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}
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if (is_hidden_global_store (stmt))
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{
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mark_stmt_necessary (stmt, true);
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return;
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}
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return;
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}
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/* Make corresponding control dependent edges necessary. We only
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have to do this once for each basic block, so we clear the bitmap
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after we're done. */
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static void
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mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el)
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{
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bitmap_iterator bi;
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unsigned edge_number;
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gcc_assert (bb != EXIT_BLOCK_PTR);
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if (bb == ENTRY_BLOCK_PTR)
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return;
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EXECUTE_IF_CONTROL_DEPENDENT (bi, bb->index, edge_number)
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{
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gimple stmt;
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basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
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if (TEST_BIT (last_stmt_necessary, cd_bb->index))
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continue;
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SET_BIT (last_stmt_necessary, cd_bb->index);
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stmt = last_stmt (cd_bb);
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if (stmt && is_ctrl_stmt (stmt))
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mark_stmt_necessary (stmt, true);
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}
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}
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/* Find obviously necessary statements. These are things like most function
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calls, and stores to file level variables.
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If EL is NULL, control statements are conservatively marked as
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necessary. Otherwise it contains the list of edges used by control
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dependence analysis. */
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static void
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find_obviously_necessary_stmts (struct edge_list *el)
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{
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basic_block bb;
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gimple_stmt_iterator gsi;
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edge e;
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gimple phi, stmt;
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FOR_EACH_BB (bb)
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{
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/* PHI nodes are never inherently necessary. */
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for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
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{
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phi = gsi_stmt (gsi);
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gimple_set_plf (phi, STMT_NECESSARY, false);
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}
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/* Check all statements in the block. */
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for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
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{
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stmt = gsi_stmt (gsi);
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gimple_set_plf (stmt, STMT_NECESSARY, false);
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mark_stmt_if_obviously_necessary (stmt, el != NULL);
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}
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}
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if (el)
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{
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/* Prevent the loops from being removed. We must keep the infinite loops,
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and we currently do not have a means to recognize the finite ones. */
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FOR_EACH_BB (bb)
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{
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edge_iterator ei;
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FOR_EACH_EDGE (e, ei, bb->succs)
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if (e->flags & EDGE_DFS_BACK)
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mark_control_dependent_edges_necessary (e->dest, el);
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}
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}
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}
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/* Propagate necessity using the operands of necessary statements.
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Process the uses on each statement in the worklist, and add all
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feeding statements which contribute to the calculation of this
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value to the worklist.
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In conservative mode, EL is NULL. */
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static void
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propagate_necessity (struct edge_list *el)
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{
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gimple stmt;
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bool aggressive = (el ? true : false);
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if (dump_file && (dump_flags & TDF_DETAILS))
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fprintf (dump_file, "\nProcessing worklist:\n");
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while (VEC_length (gimple, worklist) > 0)
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{
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/* Take STMT from worklist. */
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stmt = VEC_pop (gimple, worklist);
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if (dump_file && (dump_flags & TDF_DETAILS))
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{
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fprintf (dump_file, "processing: ");
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print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
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fprintf (dump_file, "\n");
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}
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if (aggressive)
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{
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/* Mark the last statements of the basic blocks that the block
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containing STMT is control dependent on, but only if we haven't
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already done so. */
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basic_block bb = gimple_bb (stmt);
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if (bb != ENTRY_BLOCK_PTR
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&& ! TEST_BIT (visited_control_parents, bb->index))
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{
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SET_BIT (visited_control_parents, bb->index);
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mark_control_dependent_edges_necessary (bb, el);
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}
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}
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if (gimple_code (stmt) == GIMPLE_PHI)
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{
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/* PHI nodes are somewhat special in that each PHI alternative has
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data and control dependencies. All the statements feeding the
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PHI node's arguments are always necessary. In aggressive mode,
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we also consider the control dependent edges leading to the
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predecessor block associated with each PHI alternative as
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necessary. */
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size_t k;
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for (k = 0; k < gimple_phi_num_args (stmt); k++)
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{
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tree arg = PHI_ARG_DEF (stmt, k);
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if (TREE_CODE (arg) == SSA_NAME)
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mark_operand_necessary (arg);
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}
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if (aggressive)
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{
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for (k = 0; k < gimple_phi_num_args (stmt); k++)
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{
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basic_block arg_bb = gimple_phi_arg_edge (stmt, k)->src;
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if (arg_bb != ENTRY_BLOCK_PTR
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&& ! TEST_BIT (visited_control_parents, arg_bb->index))
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{
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SET_BIT (visited_control_parents, arg_bb->index);
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mark_control_dependent_edges_necessary (arg_bb, el);
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}
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}
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}
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}
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else
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{
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/* Propagate through the operands. Examine all the USE, VUSE and
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VDEF operands in this statement. Mark all the statements
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which feed this statement's uses as necessary. The
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operands of VDEF expressions are also needed as they
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represent potential definitions that may reach this
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statement (VDEF operands allow us to follow def-def
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links). */
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ssa_op_iter iter;
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tree use;
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FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_ALL_USES)
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mark_operand_necessary (use);
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}
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}
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}
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/* Remove dead PHI nodes from block BB. */
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static bool
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remove_dead_phis (basic_block bb)
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{
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bool something_changed = false;
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gimple_seq phis;
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gimple phi;
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gimple_stmt_iterator gsi;
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phis = phi_nodes (bb);
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for (gsi = gsi_start (phis); !gsi_end_p (gsi);)
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{
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stats.total_phis++;
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phi = gsi_stmt (gsi);
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if (!gimple_plf (phi, STMT_NECESSARY))
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{
|
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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;
|
|
}
|
|
|
|
|
|
/* 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));
|
|
}
|
|
}
|
|
|
|
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);
|
|
|
|
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);
|
|
|
|
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 */
|
|
}
|
|
};
|