8d9254fc8a
From-SVN: r279813
518 lines
15 KiB
C
518 lines
15 KiB
C
/* Generic routines for manipulating PHIs
|
|
Copyright (C) 2003-2020 Free Software Foundation, Inc.
|
|
|
|
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 "backend.h"
|
|
#include "tree.h"
|
|
#include "gimple.h"
|
|
#include "ssa.h"
|
|
#include "fold-const.h"
|
|
#include "gimple-iterator.h"
|
|
#include "tree-ssa.h"
|
|
|
|
/* Rewriting a function into SSA form can create a huge number of PHIs
|
|
many of which may be thrown away shortly after their creation if jumps
|
|
were threaded through PHI nodes.
|
|
|
|
While our garbage collection mechanisms will handle this situation, it
|
|
is extremely wasteful to create nodes and throw them away, especially
|
|
when the nodes can be reused.
|
|
|
|
For PR 8361, we can significantly reduce the number of nodes allocated
|
|
and thus the total amount of memory allocated by managing PHIs a
|
|
little. This additionally helps reduce the amount of work done by the
|
|
garbage collector. Similar results have been seen on a wider variety
|
|
of tests (such as the compiler itself).
|
|
|
|
PHI nodes have different sizes, so we can't have a single list of all
|
|
the PHI nodes as it would be too expensive to walk down that list to
|
|
find a PHI of a suitable size.
|
|
|
|
Instead we have an array of lists of free PHI nodes. The array is
|
|
indexed by the number of PHI alternatives that PHI node can hold.
|
|
Except for the last array member, which holds all remaining PHI
|
|
nodes.
|
|
|
|
So to find a free PHI node, we compute its index into the free PHI
|
|
node array and see if there are any elements with an exact match.
|
|
If so, then we are done. Otherwise, we test the next larger size
|
|
up and continue until we are in the last array element.
|
|
|
|
We do not actually walk members of the last array element. While it
|
|
might allow us to pick up a few reusable PHI nodes, it could potentially
|
|
be very expensive if the program has released a bunch of large PHI nodes,
|
|
but keeps asking for even larger PHI nodes. Experiments have shown that
|
|
walking the elements of the last array entry would result in finding less
|
|
than .1% additional reusable PHI nodes.
|
|
|
|
Note that we can never have less than two PHI argument slots. Thus,
|
|
the -2 on all the calculations below. */
|
|
|
|
#define NUM_BUCKETS 10
|
|
static GTY ((deletable (""))) vec<gimple *, va_gc> *free_phinodes[NUM_BUCKETS - 2];
|
|
static unsigned long free_phinode_count;
|
|
|
|
static int ideal_phi_node_len (int);
|
|
|
|
unsigned int phi_nodes_reused;
|
|
unsigned int phi_nodes_created;
|
|
|
|
/* Dump some simple statistics regarding the re-use of PHI nodes. */
|
|
|
|
void
|
|
phinodes_print_statistics (void)
|
|
{
|
|
fprintf (stderr, "%-32s" PRsa (11) "\n", "PHI nodes allocated:",
|
|
SIZE_AMOUNT (phi_nodes_created));
|
|
fprintf (stderr, "%-32s" PRsa (11) "\n", "PHI nodes reused:",
|
|
SIZE_AMOUNT (phi_nodes_reused));
|
|
}
|
|
|
|
/* Allocate a PHI node with at least LEN arguments. If the free list
|
|
happens to contain a PHI node with LEN arguments or more, return
|
|
that one. */
|
|
|
|
static inline gphi *
|
|
allocate_phi_node (size_t len)
|
|
{
|
|
gphi *phi;
|
|
size_t bucket = NUM_BUCKETS - 2;
|
|
size_t size = sizeof (struct gphi)
|
|
+ (len - 1) * sizeof (struct phi_arg_d);
|
|
|
|
if (free_phinode_count)
|
|
for (bucket = len - 2; bucket < NUM_BUCKETS - 2; bucket++)
|
|
if (free_phinodes[bucket])
|
|
break;
|
|
|
|
/* If our free list has an element, then use it. */
|
|
if (bucket < NUM_BUCKETS - 2
|
|
&& gimple_phi_capacity ((*free_phinodes[bucket])[0]) >= len)
|
|
{
|
|
free_phinode_count--;
|
|
phi = as_a <gphi *> (free_phinodes[bucket]->pop ());
|
|
if (free_phinodes[bucket]->is_empty ())
|
|
vec_free (free_phinodes[bucket]);
|
|
if (GATHER_STATISTICS)
|
|
phi_nodes_reused++;
|
|
}
|
|
else
|
|
{
|
|
phi = static_cast <gphi *> (ggc_internal_alloc (size));
|
|
if (GATHER_STATISTICS)
|
|
{
|
|
enum gimple_alloc_kind kind = gimple_alloc_kind (GIMPLE_PHI);
|
|
phi_nodes_created++;
|
|
gimple_alloc_counts[(int) kind]++;
|
|
gimple_alloc_sizes[(int) kind] += size;
|
|
}
|
|
}
|
|
|
|
return phi;
|
|
}
|
|
|
|
/* Given LEN, the original number of requested PHI arguments, return
|
|
a new, "ideal" length for the PHI node. The "ideal" length rounds
|
|
the total size of the PHI node up to the next power of two bytes.
|
|
|
|
Rounding up will not result in wasting any memory since the size request
|
|
will be rounded up by the GC system anyway. [ Note this is not entirely
|
|
true since the original length might have fit on one of the special
|
|
GC pages. ] By rounding up, we may avoid the need to reallocate the
|
|
PHI node later if we increase the number of arguments for the PHI. */
|
|
|
|
static int
|
|
ideal_phi_node_len (int len)
|
|
{
|
|
size_t size, new_size;
|
|
int log2, new_len;
|
|
|
|
/* We do not support allocations of less than two PHI argument slots. */
|
|
if (len < 2)
|
|
len = 2;
|
|
|
|
/* Compute the number of bytes of the original request. */
|
|
size = sizeof (struct gphi)
|
|
+ (len - 1) * sizeof (struct phi_arg_d);
|
|
|
|
/* Round it up to the next power of two. */
|
|
log2 = ceil_log2 (size);
|
|
new_size = 1 << log2;
|
|
|
|
/* Now compute and return the number of PHI argument slots given an
|
|
ideal size allocation. */
|
|
new_len = len + (new_size - size) / sizeof (struct phi_arg_d);
|
|
return new_len;
|
|
}
|
|
|
|
/* Return a PHI node with LEN argument slots for variable VAR. */
|
|
|
|
static gphi *
|
|
make_phi_node (tree var, int len)
|
|
{
|
|
gphi *phi;
|
|
int capacity, i;
|
|
|
|
capacity = ideal_phi_node_len (len);
|
|
|
|
phi = allocate_phi_node (capacity);
|
|
|
|
/* We need to clear the entire PHI node, including the argument
|
|
portion, because we represent a "missing PHI argument" by placing
|
|
NULL_TREE in PHI_ARG_DEF. */
|
|
memset (phi, 0, (sizeof (struct gphi)
|
|
- sizeof (struct phi_arg_d)
|
|
+ sizeof (struct phi_arg_d) * len));
|
|
phi->code = GIMPLE_PHI;
|
|
gimple_init_singleton (phi);
|
|
phi->nargs = len;
|
|
phi->capacity = capacity;
|
|
if (!var)
|
|
;
|
|
else if (TREE_CODE (var) == SSA_NAME)
|
|
gimple_phi_set_result (phi, var);
|
|
else
|
|
gimple_phi_set_result (phi, make_ssa_name (var, phi));
|
|
|
|
for (i = 0; i < len; i++)
|
|
{
|
|
use_operand_p imm;
|
|
|
|
gimple_phi_arg_set_location (phi, i, UNKNOWN_LOCATION);
|
|
imm = gimple_phi_arg_imm_use_ptr (phi, i);
|
|
imm->use = gimple_phi_arg_def_ptr (phi, i);
|
|
imm->prev = NULL;
|
|
imm->next = NULL;
|
|
imm->loc.stmt = phi;
|
|
}
|
|
|
|
return phi;
|
|
}
|
|
|
|
/* We no longer need PHI, release it so that it may be reused. */
|
|
|
|
static void
|
|
release_phi_node (gimple *phi)
|
|
{
|
|
size_t bucket;
|
|
size_t len = gimple_phi_capacity (phi);
|
|
size_t x;
|
|
|
|
for (x = 0; x < gimple_phi_num_args (phi); x++)
|
|
{
|
|
use_operand_p imm;
|
|
imm = gimple_phi_arg_imm_use_ptr (phi, x);
|
|
delink_imm_use (imm);
|
|
}
|
|
|
|
bucket = len > NUM_BUCKETS - 1 ? NUM_BUCKETS - 1 : len;
|
|
bucket -= 2;
|
|
vec_safe_push (free_phinodes[bucket], phi);
|
|
free_phinode_count++;
|
|
}
|
|
|
|
|
|
/* Resize an existing PHI node. The only way is up. Return the
|
|
possibly relocated phi. */
|
|
|
|
static gphi *
|
|
resize_phi_node (gphi *phi, size_t len)
|
|
{
|
|
size_t old_size, i;
|
|
gphi *new_phi;
|
|
|
|
gcc_assert (len > gimple_phi_capacity (phi));
|
|
|
|
/* The garbage collector will not look at the PHI node beyond the
|
|
first PHI_NUM_ARGS elements. Therefore, all we have to copy is a
|
|
portion of the PHI node currently in use. */
|
|
old_size = sizeof (struct gphi)
|
|
+ (gimple_phi_num_args (phi) - 1) * sizeof (struct phi_arg_d);
|
|
|
|
new_phi = allocate_phi_node (len);
|
|
|
|
memcpy (new_phi, phi, old_size);
|
|
memset ((char *)new_phi + old_size, 0,
|
|
(sizeof (struct gphi)
|
|
- sizeof (struct phi_arg_d)
|
|
+ sizeof (struct phi_arg_d) * len) - old_size);
|
|
|
|
for (i = 0; i < gimple_phi_num_args (new_phi); i++)
|
|
{
|
|
use_operand_p imm, old_imm;
|
|
imm = gimple_phi_arg_imm_use_ptr (new_phi, i);
|
|
old_imm = gimple_phi_arg_imm_use_ptr (phi, i);
|
|
imm->use = gimple_phi_arg_def_ptr (new_phi, i);
|
|
relink_imm_use_stmt (imm, old_imm, new_phi);
|
|
}
|
|
|
|
new_phi->capacity = len;
|
|
|
|
return new_phi;
|
|
}
|
|
|
|
/* Reserve PHI arguments for a new edge to basic block BB. */
|
|
|
|
void
|
|
reserve_phi_args_for_new_edge (basic_block bb)
|
|
{
|
|
size_t len = EDGE_COUNT (bb->preds);
|
|
size_t cap = ideal_phi_node_len (len + 4);
|
|
gphi_iterator gsi;
|
|
|
|
for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
|
|
{
|
|
gphi *stmt = gsi.phi ();
|
|
|
|
if (len > gimple_phi_capacity (stmt))
|
|
{
|
|
gphi *new_phi = resize_phi_node (stmt, cap);
|
|
|
|
/* The result of the PHI is defined by this PHI node. */
|
|
SSA_NAME_DEF_STMT (gimple_phi_result (new_phi)) = new_phi;
|
|
gsi_set_stmt (&gsi, new_phi);
|
|
|
|
release_phi_node (stmt);
|
|
stmt = new_phi;
|
|
}
|
|
|
|
stmt->nargs++;
|
|
|
|
/* We represent a "missing PHI argument" by placing NULL_TREE in
|
|
the corresponding slot. If PHI arguments were added
|
|
immediately after an edge is created, this zeroing would not
|
|
be necessary, but unfortunately this is not the case. For
|
|
example, the loop optimizer duplicates several basic blocks,
|
|
redirects edges, and then fixes up PHI arguments later in
|
|
batch. */
|
|
use_operand_p imm = gimple_phi_arg_imm_use_ptr (stmt, len - 1);
|
|
imm->use = gimple_phi_arg_def_ptr (stmt, len - 1);
|
|
imm->prev = NULL;
|
|
imm->next = NULL;
|
|
imm->loc.stmt = stmt;
|
|
SET_PHI_ARG_DEF (stmt, len - 1, NULL_TREE);
|
|
gimple_phi_arg_set_location (stmt, len - 1, UNKNOWN_LOCATION);
|
|
}
|
|
}
|
|
|
|
/* Adds PHI to BB. */
|
|
|
|
void
|
|
add_phi_node_to_bb (gphi *phi, basic_block bb)
|
|
{
|
|
gimple_seq seq = phi_nodes (bb);
|
|
/* Add the new PHI node to the list of PHI nodes for block BB. */
|
|
if (seq == NULL)
|
|
set_phi_nodes (bb, gimple_seq_alloc_with_stmt (phi));
|
|
else
|
|
{
|
|
gimple_seq_add_stmt (&seq, phi);
|
|
gcc_assert (seq == phi_nodes (bb));
|
|
}
|
|
|
|
/* Associate BB to the PHI node. */
|
|
gimple_set_bb (phi, bb);
|
|
|
|
}
|
|
|
|
/* Create a new PHI node for variable VAR at basic block BB. */
|
|
|
|
gphi *
|
|
create_phi_node (tree var, basic_block bb)
|
|
{
|
|
gphi *phi = make_phi_node (var, EDGE_COUNT (bb->preds));
|
|
|
|
add_phi_node_to_bb (phi, bb);
|
|
return phi;
|
|
}
|
|
|
|
|
|
/* Add a new argument to PHI node PHI. DEF is the incoming reaching
|
|
definition and E is the edge through which DEF reaches PHI. The new
|
|
argument is added at the end of the argument list.
|
|
If PHI has reached its maximum capacity, add a few slots. In this case,
|
|
PHI points to the reallocated phi node when we return. */
|
|
|
|
void
|
|
add_phi_arg (gphi *phi, tree def, edge e, location_t locus)
|
|
{
|
|
basic_block bb = e->dest;
|
|
|
|
gcc_assert (bb == gimple_bb (phi));
|
|
|
|
/* We resize PHI nodes upon edge creation. We should always have
|
|
enough room at this point. */
|
|
gcc_assert (gimple_phi_num_args (phi) <= gimple_phi_capacity (phi));
|
|
|
|
/* We resize PHI nodes upon edge creation. We should always have
|
|
enough room at this point. */
|
|
gcc_assert (e->dest_idx < gimple_phi_num_args (phi));
|
|
|
|
/* Copy propagation needs to know what object occur in abnormal
|
|
PHI nodes. This is a convenient place to record such information. */
|
|
if (e->flags & EDGE_ABNORMAL)
|
|
{
|
|
SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def) = 1;
|
|
SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (phi)) = 1;
|
|
}
|
|
|
|
SET_PHI_ARG_DEF (phi, e->dest_idx, def);
|
|
gimple_phi_arg_set_location (phi, e->dest_idx, locus);
|
|
}
|
|
|
|
|
|
/* Remove the Ith argument from PHI's argument list. This routine
|
|
implements removal by swapping the last alternative with the
|
|
alternative we want to delete and then shrinking the vector, which
|
|
is consistent with how we remove an edge from the edge vector. */
|
|
|
|
static void
|
|
remove_phi_arg_num (gphi *phi, int i)
|
|
{
|
|
int num_elem = gimple_phi_num_args (phi);
|
|
|
|
gcc_assert (i < num_elem);
|
|
|
|
/* Delink the item which is being removed. */
|
|
delink_imm_use (gimple_phi_arg_imm_use_ptr (phi, i));
|
|
|
|
/* If it is not the last element, move the last element
|
|
to the element we want to delete, resetting all the links. */
|
|
if (i != num_elem - 1)
|
|
{
|
|
use_operand_p old_p, new_p;
|
|
old_p = gimple_phi_arg_imm_use_ptr (phi, num_elem - 1);
|
|
new_p = gimple_phi_arg_imm_use_ptr (phi, i);
|
|
/* Set use on new node, and link into last element's place. */
|
|
*(new_p->use) = *(old_p->use);
|
|
relink_imm_use (new_p, old_p);
|
|
/* Move the location as well. */
|
|
gimple_phi_arg_set_location (phi, i,
|
|
gimple_phi_arg_location (phi, num_elem - 1));
|
|
}
|
|
|
|
/* Shrink the vector and return. Note that we do not have to clear
|
|
PHI_ARG_DEF because the garbage collector will not look at those
|
|
elements beyond the first PHI_NUM_ARGS elements of the array. */
|
|
phi->nargs--;
|
|
}
|
|
|
|
|
|
/* Remove all PHI arguments associated with edge E. */
|
|
|
|
void
|
|
remove_phi_args (edge e)
|
|
{
|
|
gphi_iterator gsi;
|
|
|
|
for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi))
|
|
remove_phi_arg_num (gsi.phi (),
|
|
e->dest_idx);
|
|
}
|
|
|
|
|
|
/* Remove the PHI node pointed-to by iterator GSI from basic block BB. After
|
|
removal, iterator GSI is updated to point to the next PHI node in the
|
|
sequence. If RELEASE_LHS_P is true, the LHS of this PHI node is released
|
|
into the free pool of SSA names. */
|
|
|
|
void
|
|
remove_phi_node (gimple_stmt_iterator *gsi, bool release_lhs_p)
|
|
{
|
|
gimple *phi = gsi_stmt (*gsi);
|
|
|
|
if (release_lhs_p)
|
|
insert_debug_temps_for_defs (gsi);
|
|
|
|
gsi_remove (gsi, false);
|
|
|
|
/* If we are deleting the PHI node, then we should release the
|
|
SSA_NAME node so that it can be reused. */
|
|
release_phi_node (phi);
|
|
if (release_lhs_p)
|
|
release_ssa_name (gimple_phi_result (phi));
|
|
}
|
|
|
|
/* Remove all the phi nodes from BB. */
|
|
|
|
void
|
|
remove_phi_nodes (basic_block bb)
|
|
{
|
|
gphi_iterator gsi;
|
|
|
|
for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); )
|
|
remove_phi_node (&gsi, true);
|
|
|
|
set_phi_nodes (bb, NULL);
|
|
}
|
|
|
|
/* Given PHI, return its RHS if the PHI is a degenerate, otherwise return
|
|
NULL. */
|
|
|
|
tree
|
|
degenerate_phi_result (gphi *phi)
|
|
{
|
|
tree lhs = gimple_phi_result (phi);
|
|
tree val = NULL;
|
|
size_t i;
|
|
|
|
/* Ignoring arguments which are the same as LHS, if all the remaining
|
|
arguments are the same, then the PHI is a degenerate and has the
|
|
value of that common argument. */
|
|
for (i = 0; i < gimple_phi_num_args (phi); i++)
|
|
{
|
|
tree arg = gimple_phi_arg_def (phi, i);
|
|
|
|
if (arg == lhs)
|
|
continue;
|
|
else if (!arg)
|
|
break;
|
|
else if (!val)
|
|
val = arg;
|
|
else if (arg == val)
|
|
continue;
|
|
/* We bring in some of operand_equal_p not only to speed things
|
|
up, but also to avoid crashing when dereferencing the type of
|
|
a released SSA name. */
|
|
else if (TREE_CODE (val) != TREE_CODE (arg)
|
|
|| TREE_CODE (val) == SSA_NAME
|
|
|| !operand_equal_p (arg, val, 0))
|
|
break;
|
|
}
|
|
return (i == gimple_phi_num_args (phi) ? val : NULL);
|
|
}
|
|
|
|
/* Set PHI nodes of a basic block BB to SEQ. */
|
|
|
|
void
|
|
set_phi_nodes (basic_block bb, gimple_seq seq)
|
|
{
|
|
gimple_stmt_iterator i;
|
|
|
|
gcc_checking_assert (!(bb->flags & BB_RTL));
|
|
bb->il.gimple.phi_nodes = seq;
|
|
if (seq)
|
|
for (i = gsi_start (seq); !gsi_end_p (i); gsi_next (&i))
|
|
gimple_set_bb (gsi_stmt (i), bb);
|
|
}
|
|
|
|
#include "gt-tree-phinodes.h"
|