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tree-into-ssa.c
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tree-into-ssa.c
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/* Rewrite a program in Normal form into SSA.
Copyright (C) 2001, 2002, 2003, 2004, 2005, 2007, 2008, 2009, 2010, 2011
Free Software Foundation, Inc.
Contributed by Diego Novillo <dnovillo@redhat.com>
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 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
<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "flags.h"
#include "tm_p.h"
#include "langhooks.h"
#include "basic-block.h"
#include "output.h"
#include "function.h"
#include "tree-pretty-print.h"
#include "gimple-pretty-print.h"
#include "bitmap.h"
#include "tree-flow.h"
#include "gimple.h"
#include "tree-inline.h"
#include "timevar.h"
#include "hashtab.h"
#include "tree-dump.h"
#include "tree-pass.h"
#include "cfgloop.h"
#include "domwalk.h"
#include "params.h"
#include "vecprim.h"
/* This file builds the SSA form for a function as described in:
R. Cytron, J. Ferrante, B. Rosen, M. Wegman, and K. Zadeck. Efficiently
Computing Static Single Assignment Form and the Control Dependence
Graph. ACM Transactions on Programming Languages and Systems,
13(4):451-490, October 1991. */
/* Structure to map a variable VAR to the set of blocks that contain
definitions for VAR. */
struct def_blocks_d
{
/* The variable. */
tree var;
/* Blocks that contain definitions of VAR. Bit I will be set if the
Ith block contains a definition of VAR. */
bitmap def_blocks;
/* Blocks that contain a PHI node for VAR. */
bitmap phi_blocks;
/* Blocks where VAR is live-on-entry. Similar semantics as
DEF_BLOCKS. */
bitmap livein_blocks;
};
/* Each entry in DEF_BLOCKS contains an element of type STRUCT
DEF_BLOCKS_D, mapping a variable VAR to a bitmap describing all the
basic blocks where VAR is defined (assigned a new value). It also
contains a bitmap of all the blocks where VAR is live-on-entry
(i.e., there is a use of VAR in block B without a preceding
definition in B). The live-on-entry information is used when
computing PHI pruning heuristics. */
static htab_t def_blocks;
/* Stack of trees used to restore the global currdefs to its original
state after completing rewriting of a block and its dominator
children. Its elements have the following properties:
- An SSA_NAME (N) indicates that the current definition of the
underlying variable should be set to the given SSA_NAME. If the
symbol associated with the SSA_NAME is not a GIMPLE register, the
next slot in the stack must be a _DECL node (SYM). In this case,
the name N in the previous slot is the current reaching
definition for SYM.
- A _DECL node indicates that the underlying variable has no
current definition.
- A NULL node at the top entry is used to mark the last slot
associated with the current block. */
static VEC(tree,heap) *block_defs_stack;
/* Set of existing SSA names being replaced by update_ssa. */
static sbitmap old_ssa_names;
/* Set of new SSA names being added by update_ssa. Note that both
NEW_SSA_NAMES and OLD_SSA_NAMES are dense bitmaps because most of
the operations done on them are presence tests. */
static sbitmap new_ssa_names;
sbitmap interesting_blocks;
/* Set of SSA names that have been marked to be released after they
were registered in the replacement table. They will be finally
released after we finish updating the SSA web. */
static bitmap names_to_release;
static VEC(gimple_vec, heap) *phis_to_rewrite;
/* The bitmap of non-NULL elements of PHIS_TO_REWRITE. */
static bitmap blocks_with_phis_to_rewrite;
/* Growth factor for NEW_SSA_NAMES and OLD_SSA_NAMES. These sets need
to grow as the callers to register_new_name_mapping will typically
create new names on the fly. FIXME. Currently set to 1/3 to avoid
frequent reallocations but still need to find a reasonable growth
strategy. */
#define NAME_SETS_GROWTH_FACTOR (MAX (3, num_ssa_names / 3))
/* Tuple used to represent replacement mappings. */
struct repl_map_d
{
tree name;
bitmap set;
};
/* NEW -> OLD_SET replacement table. If we are replacing several
existing SSA names O_1, O_2, ..., O_j with a new name N_i,
then REPL_TBL[N_i] = { O_1, O_2, ..., O_j }. */
static htab_t repl_tbl;
/* The function the SSA updating data structures have been initialized for.
NULL if they need to be initialized by register_new_name_mapping. */
static struct function *update_ssa_initialized_fn = NULL;
/* Statistics kept by update_ssa to use in the virtual mapping
heuristic. If the number of virtual mappings is beyond certain
threshold, the updater will switch from using the mappings into
renaming the virtual symbols from scratch. In some cases, the
large number of name mappings for virtual names causes significant
slowdowns in the PHI insertion code. */
struct update_ssa_stats_d
{
unsigned num_virtual_mappings;
unsigned num_total_mappings;
bitmap virtual_symbols;
unsigned num_virtual_symbols;
};
static struct update_ssa_stats_d update_ssa_stats;
/* Global data to attach to the main dominator walk structure. */
struct mark_def_sites_global_data
{
/* This bitmap contains the variables which are set before they
are used in a basic block. */
bitmap kills;
};
/* Information stored for SSA names. */
struct ssa_name_info
{
/* The current reaching definition replacing this SSA name. */
tree current_def;
/* This field indicates whether or not the variable may need PHI nodes.
See the enum's definition for more detailed information about the
states. */
ENUM_BITFIELD (need_phi_state) need_phi_state : 2;
/* Age of this record (so that info_for_ssa_name table can be cleared
quickly); if AGE < CURRENT_INFO_FOR_SSA_NAME_AGE, then the fields
are assumed to be null. */
unsigned age;
};
/* The information associated with names. */
typedef struct ssa_name_info *ssa_name_info_p;
DEF_VEC_P (ssa_name_info_p);
DEF_VEC_ALLOC_P (ssa_name_info_p, heap);
static VEC(ssa_name_info_p, heap) *info_for_ssa_name;
static unsigned current_info_for_ssa_name_age;
/* The set of blocks affected by update_ssa. */
static bitmap blocks_to_update;
/* The main entry point to the SSA renamer (rewrite_blocks) may be
called several times to do different, but related, tasks.
Initially, we need it to rename the whole program into SSA form.
At other times, we may need it to only rename into SSA newly
exposed symbols. Finally, we can also call it to incrementally fix
an already built SSA web. */
enum rewrite_mode {
/* Convert the whole function into SSA form. */
REWRITE_ALL,
/* Incrementally update the SSA web by replacing existing SSA
names with new ones. See update_ssa for details. */
REWRITE_UPDATE
};
/* Prototypes for debugging functions. */
extern void dump_tree_ssa (FILE *);
extern void debug_tree_ssa (void);
extern void debug_def_blocks (void);
extern void dump_tree_ssa_stats (FILE *);
extern void debug_tree_ssa_stats (void);
extern void dump_update_ssa (FILE *);
extern void debug_update_ssa (void);
extern void dump_names_replaced_by (FILE *, tree);
extern void debug_names_replaced_by (tree);
extern void dump_def_blocks (FILE *);
extern void debug_def_blocks (void);
extern void dump_defs_stack (FILE *, int);
extern void debug_defs_stack (int);
extern void dump_currdefs (FILE *);
extern void debug_currdefs (void);
/* Return true if STMT needs to be rewritten. When renaming a subset
of the variables, not all statements will be processed. This is
decided in mark_def_sites. */
static inline bool
rewrite_uses_p (gimple stmt)
{
return gimple_visited_p (stmt);
}
/* Set the rewrite marker on STMT to the value given by REWRITE_P. */
static inline void
set_rewrite_uses (gimple stmt, bool rewrite_p)
{
gimple_set_visited (stmt, rewrite_p);
}
/* Return true if the DEFs created by statement STMT should be
registered when marking new definition sites. This is slightly
different than rewrite_uses_p: it's used by update_ssa to
distinguish statements that need to have both uses and defs
processed from those that only need to have their defs processed.
Statements that define new SSA names only need to have their defs
registered, but they don't need to have their uses renamed. */
static inline bool
register_defs_p (gimple stmt)
{
return gimple_plf (stmt, GF_PLF_1) != 0;
}
/* If REGISTER_DEFS_P is true, mark STMT to have its DEFs registered. */
static inline void
set_register_defs (gimple stmt, bool register_defs_p)
{
gimple_set_plf (stmt, GF_PLF_1, register_defs_p);
}
/* Get the information associated with NAME. */
static inline ssa_name_info_p
get_ssa_name_ann (tree name)
{
unsigned ver = SSA_NAME_VERSION (name);
unsigned len = VEC_length (ssa_name_info_p, info_for_ssa_name);
struct ssa_name_info *info;
if (ver >= len)
{
unsigned new_len = num_ssa_names;
VEC_reserve (ssa_name_info_p, heap, info_for_ssa_name, new_len);
while (len++ < new_len)
{
struct ssa_name_info *info = XCNEW (struct ssa_name_info);
info->age = current_info_for_ssa_name_age;
VEC_quick_push (ssa_name_info_p, info_for_ssa_name, info);
}
}
info = VEC_index (ssa_name_info_p, info_for_ssa_name, ver);
if (info->age < current_info_for_ssa_name_age)
{
info->need_phi_state = NEED_PHI_STATE_UNKNOWN;
info->current_def = NULL_TREE;
info->age = current_info_for_ssa_name_age;
}
return info;
}
/* Clears info for SSA names. */
static void
clear_ssa_name_info (void)
{
current_info_for_ssa_name_age++;
}
/* Get phi_state field for VAR. */
static inline enum need_phi_state
get_phi_state (tree var)
{
if (TREE_CODE (var) == SSA_NAME)
return get_ssa_name_ann (var)->need_phi_state;
else
return var_ann (var)->need_phi_state;
}
/* Sets phi_state field for VAR to STATE. */
static inline void
set_phi_state (tree var, enum need_phi_state state)
{
if (TREE_CODE (var) == SSA_NAME)
get_ssa_name_ann (var)->need_phi_state = state;
else
var_ann (var)->need_phi_state = state;
}
/* Return the current definition for VAR. */
tree
get_current_def (tree var)
{
if (TREE_CODE (var) == SSA_NAME)
return get_ssa_name_ann (var)->current_def;
else
return var_ann (var)->current_def;
}
/* Sets current definition of VAR to DEF. */
void
set_current_def (tree var, tree def)
{
if (TREE_CODE (var) == SSA_NAME)
get_ssa_name_ann (var)->current_def = def;
else
var_ann (var)->current_def = def;
}
/* Compute global livein information given the set of blocks where
an object is locally live at the start of the block (LIVEIN)
and the set of blocks where the object is defined (DEF_BLOCKS).
Note: This routine augments the existing local livein information
to include global livein (i.e., it modifies the underlying bitmap
for LIVEIN). */
void
compute_global_livein (bitmap livein ATTRIBUTE_UNUSED, bitmap def_blocks ATTRIBUTE_UNUSED)
{
basic_block bb, *worklist, *tos;
unsigned i;
bitmap_iterator bi;
tos = worklist
= (basic_block *) xmalloc (sizeof (basic_block) * (last_basic_block + 1));
EXECUTE_IF_SET_IN_BITMAP (livein, 0, i, bi)
*tos++ = BASIC_BLOCK (i);
/* Iterate until the worklist is empty. */
while (tos != worklist)
{
edge e;
edge_iterator ei;
/* Pull a block off the worklist. */
bb = *--tos;
/* For each predecessor block. */
FOR_EACH_EDGE (e, ei, bb->preds)
{
basic_block pred = e->src;
int pred_index = pred->index;
/* None of this is necessary for the entry block. */
if (pred != ENTRY_BLOCK_PTR
&& ! bitmap_bit_p (livein, pred_index)
&& ! bitmap_bit_p (def_blocks, pred_index))
{
*tos++ = pred;
bitmap_set_bit (livein, pred_index);
}
}
}
free (worklist);
}
/* Cleans up the REWRITE_THIS_STMT and REGISTER_DEFS_IN_THIS_STMT flags for
all statements in basic block BB. */
static void
initialize_flags_in_bb (basic_block bb)
{
gimple stmt;
gimple_stmt_iterator gsi;
for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
gimple phi = gsi_stmt (gsi);
set_rewrite_uses (phi, false);
set_register_defs (phi, false);
}
for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
stmt = gsi_stmt (gsi);
/* We are going to use the operand cache API, such as
SET_USE, SET_DEF, and FOR_EACH_IMM_USE_FAST. The operand
cache for each statement should be up-to-date. */
gcc_assert (!gimple_modified_p (stmt));
set_rewrite_uses (stmt, false);
set_register_defs (stmt, false);
}
}
/* Mark block BB as interesting for update_ssa. */
static void
mark_block_for_update (basic_block bb)
{
gcc_assert (blocks_to_update != NULL);
if (!bitmap_set_bit (blocks_to_update, bb->index))
return;
initialize_flags_in_bb (bb);
}
/* Return the set of blocks where variable VAR is defined and the blocks
where VAR is live on entry (livein). If no entry is found in
DEF_BLOCKS, a new one is created and returned. */
static inline struct def_blocks_d *
get_def_blocks_for (tree var)
{
struct def_blocks_d db, *db_p;
void **slot;
db.var = var;
slot = htab_find_slot (def_blocks, (void *) &db, INSERT);
if (*slot == NULL)
{
db_p = XNEW (struct def_blocks_d);
db_p->var = var;
db_p->def_blocks = BITMAP_ALLOC (NULL);
db_p->phi_blocks = BITMAP_ALLOC (NULL);
db_p->livein_blocks = BITMAP_ALLOC (NULL);
*slot = (void *) db_p;
}
else
db_p = (struct def_blocks_d *) *slot;
return db_p;
}
/* Mark block BB as the definition site for variable VAR. PHI_P is true if
VAR is defined by a PHI node. */
static void
set_def_block (tree var, basic_block bb, bool phi_p)
{
struct def_blocks_d *db_p;
enum need_phi_state state;
state = get_phi_state (var);
db_p = get_def_blocks_for (var);
/* Set the bit corresponding to the block where VAR is defined. */
bitmap_set_bit (db_p->def_blocks, bb->index);
if (phi_p)
bitmap_set_bit (db_p->phi_blocks, bb->index);
/* Keep track of whether or not we may need to insert PHI nodes.
If we are in the UNKNOWN state, then this is the first definition
of VAR. Additionally, we have not seen any uses of VAR yet, so
we do not need a PHI node for this variable at this time (i.e.,
transition to NEED_PHI_STATE_NO).
If we are in any other state, then we either have multiple definitions
of this variable occurring in different blocks or we saw a use of the
variable which was not dominated by the block containing the
definition(s). In this case we may need a PHI node, so enter
state NEED_PHI_STATE_MAYBE. */
if (state == NEED_PHI_STATE_UNKNOWN)
set_phi_state (var, NEED_PHI_STATE_NO);
else
set_phi_state (var, NEED_PHI_STATE_MAYBE);
}
/* Mark block BB as having VAR live at the entry to BB. */
static void
set_livein_block (tree var, basic_block bb)
{
struct def_blocks_d *db_p;
enum need_phi_state state = get_phi_state (var);
db_p = get_def_blocks_for (var);
/* Set the bit corresponding to the block where VAR is live in. */
bitmap_set_bit (db_p->livein_blocks, bb->index);
/* Keep track of whether or not we may need to insert PHI nodes.
If we reach here in NEED_PHI_STATE_NO, see if this use is dominated
by the single block containing the definition(s) of this variable. If
it is, then we remain in NEED_PHI_STATE_NO, otherwise we transition to
NEED_PHI_STATE_MAYBE. */
if (state == NEED_PHI_STATE_NO)
{
int def_block_index = bitmap_first_set_bit (db_p->def_blocks);
if (def_block_index == -1
|| ! dominated_by_p (CDI_DOMINATORS, bb,
BASIC_BLOCK (def_block_index)))
set_phi_state (var, NEED_PHI_STATE_MAYBE);
}
else
set_phi_state (var, NEED_PHI_STATE_MAYBE);
}
/* Return true if symbol SYM is marked for renaming. */
bool
symbol_marked_for_renaming (tree sym)
{
return bitmap_bit_p (SYMS_TO_RENAME (cfun), DECL_UID (sym));
}
/* Return true if NAME is in OLD_SSA_NAMES. */
static inline bool
is_old_name (tree name)
{
unsigned ver = SSA_NAME_VERSION (name);
if (!new_ssa_names)
return false;
return ver < new_ssa_names->n_bits && TEST_BIT (old_ssa_names, ver);
}
/* Return true if NAME is in NEW_SSA_NAMES. */
static inline bool
is_new_name (tree name)
{
unsigned ver = SSA_NAME_VERSION (name);
if (!new_ssa_names)
return false;
return ver < new_ssa_names->n_bits && TEST_BIT (new_ssa_names, ver);
}
/* Hashing and equality functions for REPL_TBL. */
static hashval_t
repl_map_hash (const void *p)
{
return htab_hash_pointer ((const void *)((const struct repl_map_d *)p)->name);
}
static int
repl_map_eq (const void *p1, const void *p2)
{
return ((const struct repl_map_d *)p1)->name
== ((const struct repl_map_d *)p2)->name;
}
static void
repl_map_free (void *p)
{
BITMAP_FREE (((struct repl_map_d *)p)->set);
free (p);
}
/* Return the names replaced by NEW_TREE (i.e., REPL_TBL[NEW_TREE].SET). */
static inline bitmap
names_replaced_by (tree new_tree)
{
struct repl_map_d m;
void **slot;
m.name = new_tree;
slot = htab_find_slot (repl_tbl, (void *) &m, NO_INSERT);
/* If N was not registered in the replacement table, return NULL. */
if (slot == NULL || *slot == NULL)
return NULL;
return ((struct repl_map_d *) *slot)->set;
}
/* Add OLD to REPL_TBL[NEW_TREE].SET. */
static inline void
add_to_repl_tbl (tree new_tree, tree old)
{
struct repl_map_d m, *mp;
void **slot;
m.name = new_tree;
slot = htab_find_slot (repl_tbl, (void *) &m, INSERT);
if (*slot == NULL)
{
mp = XNEW (struct repl_map_d);
mp->name = new_tree;
mp->set = BITMAP_ALLOC (NULL);
*slot = (void *) mp;
}
else
mp = (struct repl_map_d *) *slot;
bitmap_set_bit (mp->set, SSA_NAME_VERSION (old));
}
/* Add a new mapping NEW_TREE -> OLD REPL_TBL. Every entry N_i in REPL_TBL
represents the set of names O_1 ... O_j replaced by N_i. This is
used by update_ssa and its helpers to introduce new SSA names in an
already formed SSA web. */
static void
add_new_name_mapping (tree new_tree, tree old)
{
timevar_push (TV_TREE_SSA_INCREMENTAL);
/* OLD and NEW_TREE must be different SSA names for the same symbol. */
gcc_assert (new_tree != old && SSA_NAME_VAR (new_tree) == SSA_NAME_VAR (old));
/* If this mapping is for virtual names, we will need to update
virtual operands. If this is a mapping for .MEM, then we gather
the symbols associated with each name. */
if (!is_gimple_reg (new_tree))
{
tree sym;
update_ssa_stats.num_virtual_mappings++;
update_ssa_stats.num_virtual_symbols++;
/* Keep counts of virtual mappings and symbols to use in the
virtual mapping heuristic. If we have large numbers of
virtual mappings for a relatively low number of symbols, it
will make more sense to rename the symbols from scratch.
Otherwise, the insertion of PHI nodes for each of the old
names in these mappings will be very slow. */
sym = SSA_NAME_VAR (new_tree);
bitmap_set_bit (update_ssa_stats.virtual_symbols, DECL_UID (sym));
}
/* We may need to grow NEW_SSA_NAMES and OLD_SSA_NAMES because our
caller may have created new names since the set was created. */
if (new_ssa_names->n_bits <= num_ssa_names - 1)
{
unsigned int new_sz = num_ssa_names + NAME_SETS_GROWTH_FACTOR;
new_ssa_names = sbitmap_resize (new_ssa_names, new_sz, 0);
old_ssa_names = sbitmap_resize (old_ssa_names, new_sz, 0);
}
/* Update the REPL_TBL table. */
add_to_repl_tbl (new_tree, old);
/* If OLD had already been registered as a new name, then all the
names that OLD replaces should also be replaced by NEW_TREE. */
if (is_new_name (old))
bitmap_ior_into (names_replaced_by (new_tree), names_replaced_by (old));
/* Register NEW_TREE and OLD in NEW_SSA_NAMES and OLD_SSA_NAMES,
respectively. */
SET_BIT (new_ssa_names, SSA_NAME_VERSION (new_tree));
SET_BIT (old_ssa_names, SSA_NAME_VERSION (old));
/* Update mapping counter to use in the virtual mapping heuristic. */
update_ssa_stats.num_total_mappings++;
timevar_pop (TV_TREE_SSA_INCREMENTAL);
}
/* Call back for walk_dominator_tree used to collect definition sites
for every variable in the function. For every statement S in block
BB:
1- Variables defined by S in the DEFS of S are marked in the bitmap
KILLS.
2- If S uses a variable VAR and there is no preceding kill of VAR,
then it is marked in the LIVEIN_BLOCKS bitmap associated with VAR.
This information is used to determine which variables are live
across block boundaries to reduce the number of PHI nodes
we create. */
static void
mark_def_sites (basic_block bb, gimple stmt, bitmap kills)
{
tree def;
use_operand_p use_p;
ssa_op_iter iter;
/* Since this is the first time that we rewrite the program into SSA
form, force an operand scan on every statement. */
update_stmt (stmt);
gcc_assert (blocks_to_update == NULL);
set_register_defs (stmt, false);
set_rewrite_uses (stmt, false);
if (is_gimple_debug (stmt))
{
FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE)
{
tree sym = USE_FROM_PTR (use_p);
gcc_assert (DECL_P (sym));
set_rewrite_uses (stmt, true);
}
if (rewrite_uses_p (stmt))
SET_BIT (interesting_blocks, bb->index);
return;
}
/* If a variable is used before being set, then the variable is live
across a block boundary, so mark it live-on-entry to BB. */
FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE)
{
tree sym = USE_FROM_PTR (use_p);
gcc_assert (DECL_P (sym));
if (!bitmap_bit_p (kills, DECL_UID (sym)))
set_livein_block (sym, bb);
set_rewrite_uses (stmt, true);
}
/* Now process the defs. Mark BB as the definition block and add
each def to the set of killed symbols. */
FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
{
gcc_assert (DECL_P (def));
set_def_block (def, bb, false);
bitmap_set_bit (kills, DECL_UID (def));
set_register_defs (stmt, true);
}
/* If we found the statement interesting then also mark the block BB
as interesting. */
if (rewrite_uses_p (stmt) || register_defs_p (stmt))
SET_BIT (interesting_blocks, bb->index);
}
/* Structure used by prune_unused_phi_nodes to record bounds of the intervals
in the dfs numbering of the dominance tree. */
struct dom_dfsnum
{
/* Basic block whose index this entry corresponds to. */
unsigned bb_index;
/* The dfs number of this node. */
unsigned dfs_num;
};
/* Compares two entries of type struct dom_dfsnum by dfs_num field. Callback
for qsort. */
static int
cmp_dfsnum (const void *a, const void *b)
{
const struct dom_dfsnum *const da = (const struct dom_dfsnum *) a;
const struct dom_dfsnum *const db = (const struct dom_dfsnum *) b;
return (int) da->dfs_num - (int) db->dfs_num;
}
/* Among the intervals starting at the N points specified in DEFS, find
the one that contains S, and return its bb_index. */
static unsigned
find_dfsnum_interval (struct dom_dfsnum *defs, unsigned n, unsigned s)
{
unsigned f = 0, t = n, m;
while (t > f + 1)
{
m = (f + t) / 2;
if (defs[m].dfs_num <= s)
f = m;
else
t = m;
}
return defs[f].bb_index;
}
/* Clean bits from PHIS for phi nodes whose value cannot be used in USES.
KILLS is a bitmap of blocks where the value is defined before any use. */
static void
prune_unused_phi_nodes (bitmap phis, bitmap kills, bitmap uses)
{
VEC(int, heap) *worklist;
bitmap_iterator bi;
unsigned i, b, p, u, top;
bitmap live_phis;
basic_block def_bb, use_bb;
edge e;
edge_iterator ei;
bitmap to_remove;
struct dom_dfsnum *defs;
unsigned n_defs, adef;
if (bitmap_empty_p (uses))
{
bitmap_clear (phis);
return;
}
/* The phi must dominate a use, or an argument of a live phi. Also, we
do not create any phi nodes in def blocks, unless they are also livein. */
to_remove = BITMAP_ALLOC (NULL);
bitmap_and_compl (to_remove, kills, uses);
bitmap_and_compl_into (phis, to_remove);
if (bitmap_empty_p (phis))
{
BITMAP_FREE (to_remove);
return;
}
/* We want to remove the unnecessary phi nodes, but we do not want to compute
liveness information, as that may be linear in the size of CFG, and if
there are lot of different variables to rewrite, this may lead to quadratic
behavior.
Instead, we basically emulate standard dce. We put all uses to worklist,
then for each of them find the nearest def that dominates them. If this
def is a phi node, we mark it live, and if it was not live before, we
add the predecessors of its basic block to the worklist.
To quickly locate the nearest def that dominates use, we use dfs numbering
of the dominance tree (that is already available in order to speed up
queries). For each def, we have the interval given by the dfs number on
entry to and on exit from the corresponding subtree in the dominance tree.
The nearest dominator for a given use is the smallest of these intervals
that contains entry and exit dfs numbers for the basic block with the use.
If we store the bounds for all the uses to an array and sort it, we can
locate the nearest dominating def in logarithmic time by binary search.*/
bitmap_ior (to_remove, kills, phis);
n_defs = bitmap_count_bits (to_remove);
defs = XNEWVEC (struct dom_dfsnum, 2 * n_defs + 1);
defs[0].bb_index = 1;
defs[0].dfs_num = 0;
adef = 1;
EXECUTE_IF_SET_IN_BITMAP (to_remove, 0, i, bi)
{
def_bb = BASIC_BLOCK (i);
defs[adef].bb_index = i;
defs[adef].dfs_num = bb_dom_dfs_in (CDI_DOMINATORS, def_bb);
defs[adef + 1].bb_index = i;
defs[adef + 1].dfs_num = bb_dom_dfs_out (CDI_DOMINATORS, def_bb);
adef += 2;
}
BITMAP_FREE (to_remove);
gcc_assert (adef == 2 * n_defs + 1);
qsort (defs, adef, sizeof (struct dom_dfsnum), cmp_dfsnum);
gcc_assert (defs[0].bb_index == 1);
/* Now each DEFS entry contains the number of the basic block to that the
dfs number corresponds. Change them to the number of basic block that
corresponds to the interval following the dfs number. Also, for the
dfs_out numbers, increase the dfs number by one (so that it corresponds
to the start of the following interval, not to the end of the current
one). We use WORKLIST as a stack. */
worklist = VEC_alloc (int, heap, n_defs + 1);
VEC_quick_push (int, worklist, 1);
top = 1;
n_defs = 1;
for (i = 1; i < adef; i++)
{
b = defs[i].bb_index;
if (b == top)
{
/* This is a closing element. Interval corresponding to the top
of the stack after removing it follows. */
VEC_pop (int, worklist);
top = VEC_index (int, worklist, VEC_length (int, worklist) - 1);
defs[n_defs].bb_index = top;
defs[n_defs].dfs_num = defs[i].dfs_num + 1;
}
else
{
/* Opening element. Nothing to do, just push it to the stack and move
it to the correct position. */
defs[n_defs].bb_index = defs[i].bb_index;
defs[n_defs].dfs_num = defs[i].dfs_num;
VEC_quick_push (int, worklist, b);
top = b;
}
/* If this interval starts at the same point as the previous one, cancel
the previous one. */
if (defs[n_defs].dfs_num == defs[n_defs - 1].dfs_num)
defs[n_defs - 1].bb_index = defs[n_defs].bb_index;
else
n_defs++;
}
VEC_pop (int, worklist);
gcc_assert (VEC_empty (int, worklist));
/* Now process the uses. */
live_phis = BITMAP_ALLOC (NULL);
EXECUTE_IF_SET_IN_BITMAP (uses, 0, i, bi)
{
VEC_safe_push (int, heap, worklist, i);
}
while (!VEC_empty (int, worklist))
{
b = VEC_pop (int, worklist);
if (b == ENTRY_BLOCK)
continue;
/* If there is a phi node in USE_BB, it is made live. Otherwise,
find the def that dominates the immediate dominator of USE_BB
(the kill in USE_BB does not dominate the use). */
if (bitmap_bit_p (phis, b))
p = b;
else
{
use_bb = get_immediate_dominator (CDI_DOMINATORS, BASIC_BLOCK (b));
p = find_dfsnum_interval (defs, n_defs,
bb_dom_dfs_in (CDI_DOMINATORS, use_bb));
if (!bitmap_bit_p (phis, p))
continue;
}
/* If the phi node is already live, there is nothing to do. */
if (!bitmap_set_bit (live_phis, p))
continue;
/* Add the new uses to the worklist. */
def_bb = BASIC_BLOCK (p);
FOR_EACH_EDGE (e, ei, def_bb->preds)
{
u = e->src->index;
if (bitmap_bit_p (uses, u))
continue;
/* In case there is a kill directly in the use block, do not record
the use (this is also necessary for correctness, as we assume that
uses dominated by a def directly in their block have been filtered
out before). */
if (bitmap_bit_p (kills, u))
continue;
bitmap_set_bit (uses, u);
VEC_safe_push (int, heap, worklist, u);
}
}
VEC_free (int, heap, worklist);
bitmap_copy (phis, live_phis);
BITMAP_FREE (live_phis);
free (defs);
}