/* Dead code elimination pass for the GNU compiler.
- Copyright (C) 2002, 2003, 2004 Free Software Foundation, Inc.
+ Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007
+ 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.
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
+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
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, 59 Temple Place - Suite 330, Boston, MA
-02111-1307, USA. */
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
/* Dead code elimination.
#include "system.h"
#include "coretypes.h"
#include "tm.h"
-#include "errors.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-simple.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"
\f
static struct stmt_stats
{
int removed_phis;
} stats;
-static varray_type worklist;
+static VEC(tree,heap) *worklist;
/* Vector indicating an SSA name has already been processed and marked
as necessary. */
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. */
-bitmap *control_dependence_map;
+static bitmap *control_dependence_map;
-/* Execute CODE 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(N, EDGE_NUMBER, CODE) \
- EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[N], 0, EDGE_NUMBER, CODE)
+/* Vector indicating that a basic block has already had all the edges
+ processed that it is control dependent on. */
+static sbitmap visited_control_parents;
-/* 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);
+/* TRUE if this pass alters the CFG (by removing control statements).
+ FALSE otherwise.
-static inline void mark_stmt_necessary (tree, bool);
-static inline void mark_operand_necessary (tree);
+ If this pass alters the CFG, then it will arrange for the dominators
+ to be recomputed. */
+static bool cfg_altered;
-static bool need_to_preserve_store (tree);
-static void mark_stmt_if_obviously_necessary (tree, bool);
-static void find_obviously_necessary_stmts (struct edge_list *);
+/* 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))
-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);
-\f
/* 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;
- if (bb == EXIT_BLOCK_PTR)
- abort ();
+ 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)
+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)
+/* 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)
{
- int i;
+ gcc_assert (block != ENTRY_BLOCK_PTR);
- for (i = 0; i < NUM_EDGES (el); ++i)
- find_control_dependence (el, i);
+ 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. */
basic_block current_block;
basic_block ending_block;
-#ifdef ENABLE_CHECKING
- if (INDEX_EDGE_PRED_BB (el, edge_index) == EXIT_BLOCK_PTR)
- abort ();
-#endif
+ 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 = ENTRY_BLOCK_PTR->next_bb;
+ ending_block = single_succ (ENTRY_BLOCK_PTR);
else
ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, 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)
+/* 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)
{
- if (block == ENTRY_BLOCK_PTR)
- abort ();
- else 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;
- }
+ int i;
+
+ for (i = 0; i < NUM_EDGES (el); ++i)
+ find_control_dependence (el, i);
}
-\f
-#define NECESSARY(stmt) stmt->common.asm_written_flag
+
+
+#define NECESSARY(stmt) stmt->base.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)
{
-#ifdef ENABLE_CHECKING
- if (stmt == NULL
- || stmt == error_mark_node
- || (stmt && DECL_P (stmt)))
- abort ();
-#endif
+ gcc_assert (stmt);
+ gcc_assert (!DECL_P (stmt));
if (NECESSARY (stmt))
return;
NECESSARY (stmt) = 1;
if (add_to_worklist)
- VARRAY_PUSH_TREE (worklist, stmt);
+ VEC_safe_push (tree, heap, worklist, stmt);
}
+
/* Mark the statement defining operand OP as necessary. */
static inline void
tree stmt;
int ver;
-#ifdef ENABLE_CHECKING
- if (op == NULL)
- abort ();
-#endif
+ gcc_assert (op);
ver = SSA_NAME_VERSION (op);
if (TEST_BIT (processed, ver))
SET_BIT (processed, ver);
stmt = SSA_NAME_DEF_STMT (op);
-#ifdef ENABLE_CHECKING
- if (stmt == NULL)
- abort ();
-#endif
+ gcc_assert (stmt);
- if (NECESSARY (stmt)
- || IS_EMPTY_STMT (stmt))
+ if (NECESSARY (stmt) || IS_EMPTY_STMT (stmt))
return;
NECESSARY (stmt) = 1;
- VARRAY_PUSH_TREE (worklist, stmt);
+ VEC_safe_push (tree, heap, worklist, stmt);
}
-\f
-/* Return true if a store to a variable needs to be preserved. */
-static inline bool
-need_to_preserve_store (tree ssa_name)
-{
- return (needs_to_live_in_memory (SSA_NAME_VAR (ssa_name)));
-}
-\f
-/* Mark STMT as necessary if it is obviously is. Add it to the worklist if
+/* 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
static void
mark_stmt_if_obviously_necessary (tree stmt, bool aggressive)
{
- def_optype defs;
- vdef_optype vdefs;
stmt_ann_t ann;
- size_t i;
+ 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
case ASM_EXPR:
case RESX_EXPR:
case RETURN_EXPR:
+ case CHANGE_DYNAMIC_TYPE_EXPR:
mark_stmt_necessary (stmt, true);
return;
mark_stmt_necessary (stmt, true);
return;
- case MODIFY_EXPR:
- if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR
- && TREE_SIDE_EFFECTS (TREE_OPERAND (stmt, 1)))
+ case GIMPLE_MODIFY_STMT:
+ 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)
+ if (TREE_CODE (GIMPLE_STMT_OPERAND (stmt, 0)) == EXC_PTR_EXPR
+ || TREE_CODE (GIMPLE_STMT_OPERAND (stmt, 0)) == FILTER_EXPR)
{
mark_stmt_necessary (stmt, true);
return;
break;
case GOTO_EXPR:
- if (! simple_goto_p (stmt))
- mark_stmt_necessary (stmt, true);
+ gcc_assert (!simple_goto_p (stmt));
+ mark_stmt_necessary (stmt, true);
return;
case COND_EXPR:
- if (GOTO_DESTINATION (COND_EXPR_THEN (stmt))
- == GOTO_DESTINATION (COND_EXPR_ELSE (stmt)))
- {
- /* A COND_EXPR is obviously dead if the target labels are the same.
- We cannot kill the statement at this point, so to prevent the
- statement from being marked necessary, we replace the condition
- with a constant. The stmt is killed later on in cfg_cleanup. */
- COND_EXPR_COND (stmt) = integer_zero_node;
- modify_stmt (stmt);
- return;
- }
+ gcc_assert (EDGE_COUNT (bb_for_stmt (stmt)->succs) == 2);
/* Fall through. */
case SWITCH_EXPR:
}
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))
+
+ /* 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;
}
- get_stmt_operands (stmt);
-
- defs = DEF_OPS (ann);
- for (i = 0; i < NUM_DEFS (defs); i++)
+ if (is_hidden_global_store (stmt))
{
- tree def = DEF_OP (defs, i);
- if (need_to_preserve_store (def))
- {
- mark_stmt_necessary (stmt, true);
- return;
- }
+ mark_stmt_necessary (stmt, true);
+ return;
}
- vdefs = VDEF_OPS (ann);
- for (i = 0; i < NUM_VDEFS (vdefs); i++)
+ 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)
{
- tree vdef = VDEF_RESULT (vdefs, i);
- if (need_to_preserve_store (vdef))
- {
- mark_stmt_necessary (stmt, true);
- return;
- }
- }
+ tree t;
+ basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
- return;
+ 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);
+ }
}
-\f
+
+
/* Find obviously necessary statements. These are things like most function
calls, and stores to file level variables.
{
tree phi;
- /* Check any PHI nodes in the block. */
- for (phi = phi_nodes (bb); phi; phi = TREE_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))
- && need_to_preserve_store (PHI_RESULT (phi)))
- mark_stmt_necessary (phi, true);
- }
+ /* PHI nodes are never inherently necessary. */
+ for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
+ NECESSARY (phi) = 0;
/* Check all statements in the block. */
for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i))
NECESSARY (stmt) = 0;
mark_stmt_if_obviously_necessary (stmt, el != NULL);
}
-
- /* Mark this basic block as `not visited'. A block will be marked
- visited when the edges that it is control dependent on have been
- marked. */
- bb->flags &= ~BB_VISITED;
}
if (el)
and we currently do not have a means to recognize the finite ones. */
FOR_EACH_BB (bb)
{
- for (e = bb->succ; e; e = e->succ_next)
+ edge_iterator ei;
+ FOR_EACH_EDGE (e, ei, bb->succs)
if (e->flags & EDGE_DFS_BACK)
mark_control_dependent_edges_necessary (e->dest, el);
}
}
}
-\f
-/* 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)
-{
- int edge_number;
- EXECUTE_IF_CONTROL_DEPENDENT (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 (is_ctrl_stmt (t))
- mark_stmt_necessary (t, true);
- });
-}
-\f
-/* 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.
+/* 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;
+ tree stmt;
bool aggressive = (el ? true : false);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "\nProcessing worklist:\n");
- while (VARRAY_ACTIVE_SIZE (worklist) > 0)
+ while (VEC_length (tree, worklist) > 0)
{
- /* Take `i' from worklist. */
- i = VARRAY_TOP_TREE (worklist);
- VARRAY_POP (worklist);
+ /* Take STMT from worklist. */
+ stmt = VEC_pop (tree, worklist);
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "processing: ");
- print_generic_stmt (dump_file, i, TDF_SLIM);
+ print_generic_stmt (dump_file, stmt, 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
+ containing STMT is control dependent on, but only if we haven't
already done so. */
- basic_block bb = bb_for_stmt (i);
- if (! (bb->flags & BB_VISITED))
+ basic_block bb = bb_for_stmt (stmt);
+ if (bb != ENTRY_BLOCK_PTR
+ && ! TEST_BIT (visited_control_parents, bb->index))
{
- bb->flags |= BB_VISITED;
+ SET_BIT (visited_control_parents, bb->index);
mark_control_dependent_edges_necessary (bb, el);
}
}
- if (TREE_CODE (i) == PHI_NODE)
+ if (TREE_CODE (stmt) == PHI_NODE)
{
/* PHI nodes are somewhat special in that each PHI alternative has
data and control dependencies. All the statements feeding the
predecessor block associated with each PHI alternative as
necessary. */
int k;
- for (k = 0; k < PHI_NUM_ARGS (i); k++)
+
+ for (k = 0; k < PHI_NUM_ARGS (stmt); k++)
{
- tree arg = PHI_ARG_DEF (i, k);
+ tree arg = PHI_ARG_DEF (stmt, k);
if (TREE_CODE (arg) == SSA_NAME)
mark_operand_necessary (arg);
}
if (aggressive)
{
- for (k = 0; k < PHI_NUM_ARGS (i); k++)
+ for (k = 0; k < PHI_NUM_ARGS (stmt); k++)
{
- basic_block arg_bb = PHI_ARG_EDGE (i, k)->src;
- if (! (arg_bb->flags & BB_VISITED))
+ basic_block arg_bb = PHI_ARG_EDGE (stmt, k)->src;
+ if (arg_bb != ENTRY_BLOCK_PTR
+ && ! TEST_BIT (visited_control_parents, arg_bb->index))
{
- arg_bb->flags |= BB_VISITED;
+ 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. */
- vuse_optype vuses;
- vdef_optype vdefs;
- use_optype uses;
- stmt_ann_t ann;
- size_t k;
-
- get_stmt_operands (i);
- ann = stmt_ann (i);
-
- uses = USE_OPS (ann);
- for (k = 0; k < NUM_USES (uses); k++)
- mark_operand_necessary (USE_OP (uses, k));
-
- vuses = VUSE_OPS (ann);
- for (k = 0; k < NUM_VUSES (vuses); k++)
- mark_operand_necessary (VUSE_OP (vuses, k));
-
- /* The operands of VDEF expressions are also needed as they
+ 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). */
- vdefs = VDEF_OPS (ann);
- for (k = 0; k < NUM_VDEFS (vdefs); k++)
- mark_operand_necessary (VDEF_OP (vdefs, k));
+ statement (VDEF operands allow us to follow def-def
+ links). */
+ ssa_op_iter iter;
+ tree use;
+
+ FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_ALL_USES)
+ mark_operand_necessary (use);
}
}
}
-\f
-/* 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);
-
- /* 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
- {
- if (TREE_CODE (t) == CALL_EXPR)
- notice_special_calls (t);
- else if (TREE_CODE (t) == MODIFY_EXPR
- && TREE_CODE (TREE_OPERAND (t, 1)) == CALL_EXPR)
- notice_special_calls (TREE_OPERAND (t, 1));
- bsi_next (&i);
- }
- }
- }
-}
-\f
/* Remove dead PHI nodes from block BB. */
-static void
+static bool
remove_dead_phis (basic_block bb)
{
tree prev, phi;
+ bool something_changed = false;
prev = NULL_TREE;
phi = phi_nodes (bb);
if (! NECESSARY (phi))
{
- tree next = TREE_CHAIN (phi);
+ tree next = PHI_CHAIN (phi);
+ something_changed = true;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Deleting : ");
fprintf (dump_file, "\n");
}
- remove_phi_node (phi, prev, bb);
+ remove_phi_node (phi, prev, true);
stats.removed_phis++;
phi = next;
}
else
{
prev = phi;
- phi = TREE_CHAIN (phi);
+ phi = PHI_CHAIN (phi);
}
}
+ return something_changed;
}
-\f
-/* Remove dead statement pointed by iterator I. Receives the basic block BB
+
+
+/* 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
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 cleaup_cfg if this change in the flow graph makes them
+ 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;
- edge e;
-#ifdef ENABLE_CHECKING
+
/* The post dominance info has to be up-to-date. */
- if (dom_computed[CDI_POST_DOMINATORS] != DOM_OK)
- abort ();
-#endif
+ 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);
- /* Some blocks don't have an immediate post dominator. This can happen
- for example with infinite loops. Removing an infinite loop is an
- inappropriate transformation anyway... */
- if (! post_dom_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
{
- bsi_next (i);
- return;
+ /* 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;
}
-
- /* Redirect the first edge out of BB to reach POST_DOM_BB. */
- redirect_edge_and_branch (bb->succ, post_dom_bb);
- PENDING_STMT (bb->succ) = 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. */
- bb->succ->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
+ EDGE_SUCC (bb, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
- /* If the edge reaches any block other than the exit, then it is a
- fallthru edge; if it reaches the exit, then it is not a fallthru
- edge. */
- if (post_dom_bb != EXIT_BLOCK_PTR)
- bb->succ->flags |= EDGE_FALLTHRU;
- else
- bb->succ->flags &= ~EDGE_FALLTHRU;
+ /* The lone outgoing edge from BB will be a fallthru edge. */
+ EDGE_SUCC (bb, 0)->flags |= EDGE_FALLTHRU;
/* Remove the remaining the outgoing edges. */
- for (e = bb->succ->succ_next; e != NULL;)
+ while (!single_succ_p (bb))
{
- edge tmp = e;
- e = e->succ_next;
- remove_edge (tmp);
+ /* 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));
}
}
+
+ bsi_remove (i, true);
+ release_defs (t);
+}
+
+
+/* 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;
+ block_stmt_iterator i;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, "\nEliminating unnecessary statements:\n");
- bsi_remove (i);
+ 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 (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);
+ something_changed = true;
+ }
+ else
+ {
+ tree call = get_call_expr_in (t);
+ if (call)
+ {
+ tree name;
+
+ /* When LHS of var = call (); is dead, simplify it into
+ call (); saving one operand. */
+ if (TREE_CODE (t) == GIMPLE_MODIFY_STMT
+ && (TREE_CODE ((name = GIMPLE_STMT_OPERAND (t, 0)))
+ == SSA_NAME)
+ && !TEST_BIT (processed, SSA_NAME_VERSION (name)))
+ {
+ tree oldlhs = GIMPLE_STMT_OPERAND (t, 0);
+ something_changed = true;
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Deleting LHS of call: ");
+ print_generic_stmt (dump_file, t, TDF_SLIM);
+ fprintf (dump_file, "\n");
+ }
+ push_stmt_changes (bsi_stmt_ptr (i));
+ TREE_BLOCK (call) = TREE_BLOCK (t);
+ bsi_replace (&i, call, false);
+ maybe_clean_or_replace_eh_stmt (t, call);
+ mark_symbols_for_renaming (call);
+ pop_stmt_changes (bsi_stmt_ptr (i));
+ release_ssa_name (oldlhs);
+ }
+ notice_special_calls (call);
+ }
+ bsi_next (&i);
+ }
+ }
+ }
+
+ return something_changed;
}
-\f
+
+
/* Print out removed statement statistics. */
static void
{
int i;
- control_dependence_map
- = xmalloc (last_basic_block * sizeof (bitmap));
+ control_dependence_map = XNEWVEC (bitmap, last_basic_block);
for (i = 0; i < last_basic_block; ++i)
- control_dependence_map[i] = BITMAP_XMALLOC ();
+ control_dependence_map[i] = BITMAP_ALLOC (NULL);
last_stmt_necessary = sbitmap_alloc (last_basic_block);
sbitmap_zero (last_stmt_necessary);
}
- processed = sbitmap_alloc (highest_ssa_version + 1);
+ processed = sbitmap_alloc (num_ssa_names + 1);
sbitmap_zero (processed);
- VARRAY_TREE_INIT (worklist, 64, "work list");
+ worklist = VEC_alloc (tree, heap, 64);
+ cfg_altered = false;
}
/* Cleanup after this pass. */
int i;
for (i = 0; i < last_basic_block; ++i)
- BITMAP_XFREE (control_dependence_map[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);
}
\f
/* Main routine to eliminate dead code.
as the last tree SSA pass, but keep this in mind when you
start experimenting with pass ordering. */
-static void
+static unsigned int
perform_tree_ssa_dce (bool aggressive)
{
struct edge_list *el = NULL;
+ bool something_changed = 0;
tree_dce_init (aggressive);
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 ();
}
propagate_necessity (el);
- eliminate_unnecessary_stmts ();
+ something_changed |= eliminate_unnecessary_stmts ();
+ something_changed |= cfg_altered;
- if (aggressive)
- free_dominance_info (CDI_POST_DOMINATORS);
+ /* We do not update postdominators, so free them unconditionally. */
+ free_dominance_info (CDI_POST_DOMINATORS);
- cleanup_tree_cfg ();
+ /* 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)
- {
- dump_function_to_file (current_function_decl, dump_file, dump_flags);
- print_stats ();
- }
+ 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 void
+static unsigned int
tree_ssa_dce (void)
{
- perform_tree_ssa_dce (/*aggressive=*/false);
+ return perform_tree_ssa_dce (/*aggressive=*/false);
}
-static void
+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)
{
- perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
+ return perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
}
static bool
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
- TODO_ggc_collect | TODO_verify_ssa /* todo_flags_finish */
+ TODO_dump_func | TODO_verify_ssa, /* 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, /* properties_required */
+ 0, /* properties_provided */
+ 0, /* properties_destroyed */
+ 0, /* todo_flags_start */
+ TODO_dump_func | TODO_verify_ssa, /* todo_flags_finish */
+ 0 /* letter */
};
struct tree_opt_pass pass_cd_dce =
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
- TODO_ggc_collect | TODO_verify_ssa | TODO_verify_flow
- /* todo_flags_finish */
+ TODO_dump_func | TODO_verify_ssa
+ | TODO_verify_flow, /* todo_flags_finish */
+ 0 /* letter */
};
-
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