freebsd-dev/contrib/gcc/tree-ssa-loop-unswitch.c
2007-05-19 01:19:51 +00:00

293 lines
7.2 KiB
C

/* Loop unswitching.
Copyright (C) 2004, 2005 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 2, 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 COPYING. If not, write to the Free
Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "rtl.h"
#include "tm_p.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "output.h"
#include "diagnostic.h"
#include "tree-flow.h"
#include "tree-dump.h"
#include "timevar.h"
#include "cfgloop.h"
#include "domwalk.h"
#include "params.h"
#include "tree-pass.h"
/* This file implements the loop unswitching, i.e. transformation of loops like
while (A)
{
if (inv)
B;
X;
if (!inv)
C;
}
where inv is the loop invariant, into
if (inv)
{
while (A)
{
B;
X;
}
}
else
{
while (A)
{
X;
C;
}
}
Inv is considered invariant iff the values it compares are both invariant;
tree-ssa-loop-im.c ensures that all the suitable conditions are in this
shape. */
static struct loop *tree_unswitch_loop (struct loops *, struct loop *, basic_block,
tree);
static bool tree_unswitch_single_loop (struct loops *, struct loop *, int);
static tree tree_may_unswitch_on (basic_block, struct loop *);
/* Main entry point. Perform loop unswitching on all suitable LOOPS. */
unsigned int
tree_ssa_unswitch_loops (struct loops *loops)
{
int i, num;
struct loop *loop;
bool changed = false;
/* Go through inner loops (only original ones). */
num = loops->num;
for (i = 1; i < num; i++)
{
/* Removed loop? */
loop = loops->parray[i];
if (!loop)
continue;
if (loop->inner)
continue;
changed |= tree_unswitch_single_loop (loops, loop, 0);
}
if (changed)
return TODO_cleanup_cfg;
return 0;
}
/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its
basic blocks (for what it means see comments below). */
static tree
tree_may_unswitch_on (basic_block bb, struct loop *loop)
{
tree stmt, def, cond, use;
basic_block def_bb;
ssa_op_iter iter;
/* BB must end in a simple conditional jump. */
stmt = last_stmt (bb);
if (!stmt || TREE_CODE (stmt) != COND_EXPR)
return NULL_TREE;
/* Condition must be invariant. */
FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
{
def = SSA_NAME_DEF_STMT (use);
def_bb = bb_for_stmt (def);
if (def_bb
&& flow_bb_inside_loop_p (loop, def_bb))
return NULL_TREE;
}
cond = COND_EXPR_COND (stmt);
/* To keep the things simple, we do not directly remove the conditions,
but just replace tests with 0/1. Prevent the infinite loop where we
would unswitch again on such a condition. */
if (integer_zerop (cond) || integer_nonzerop (cond))
return NULL_TREE;
return cond;
}
/* Simplifies COND using checks in front of the entry of the LOOP. Just very
simplish (sufficient to prevent us from duplicating loop in unswitching
unnecessarily). */
static tree
simplify_using_entry_checks (struct loop *loop, tree cond)
{
edge e = loop_preheader_edge (loop);
tree stmt;
while (1)
{
stmt = last_stmt (e->src);
if (stmt
&& TREE_CODE (stmt) == COND_EXPR
&& operand_equal_p (COND_EXPR_COND (stmt), cond, 0))
return (e->flags & EDGE_TRUE_VALUE
? boolean_true_node
: boolean_false_node);
if (!single_pred_p (e->src))
return cond;
e = single_pred_edge (e->src);
if (e->src == ENTRY_BLOCK_PTR)
return cond;
}
}
/* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow
it to grow too much, it is too easy to create example on that the code would
grow exponentially. */
static bool
tree_unswitch_single_loop (struct loops *loops, struct loop *loop, int num)
{
basic_block *bbs;
struct loop *nloop;
unsigned i;
tree cond = NULL_TREE, stmt;
bool changed = false;
/* Do not unswitch too much. */
if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL))
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, ";; Not unswitching anymore, hit max level\n");
return false;
}
/* Only unswitch innermost loops. */
if (loop->inner)
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, ";; Not unswitching, not innermost loop\n");
return false;
}
/* The loop should not be too large, to limit code growth. */
if (tree_num_loop_insns (loop)
> (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS))
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, ";; Not unswitching, loop too big\n");
return false;
}
i = 0;
bbs = get_loop_body (loop);
while (1)
{
/* Find a bb to unswitch on. */
for (; i < loop->num_nodes; i++)
if ((cond = tree_may_unswitch_on (bbs[i], loop)))
break;
if (i == loop->num_nodes)
{
free (bbs);
return changed;
}
cond = simplify_using_entry_checks (loop, cond);
stmt = last_stmt (bbs[i]);
if (integer_nonzerop (cond))
{
/* Remove false path. */
COND_EXPR_COND (stmt) = boolean_true_node;
changed = true;
}
else if (integer_zerop (cond))
{
/* Remove true path. */
COND_EXPR_COND (stmt) = boolean_false_node;
changed = true;
}
else
break;
update_stmt (stmt);
i++;
}
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, ";; Unswitching loop\n");
initialize_original_copy_tables ();
/* Unswitch the loop on this condition. */
nloop = tree_unswitch_loop (loops, loop, bbs[i], cond);
if (!nloop)
{
free_original_copy_tables ();
free (bbs);
return changed;
}
/* Update the SSA form after unswitching. */
update_ssa (TODO_update_ssa);
free_original_copy_tables ();
/* Invoke itself on modified loops. */
tree_unswitch_single_loop (loops, nloop, num + 1);
tree_unswitch_single_loop (loops, loop, num + 1);
free (bbs);
return true;
}
/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support
unswitching of innermost loops. COND is the condition determining which
loop is entered -- the new loop is entered if COND is true. Returns NULL
if impossible, new loop otherwise. */
static struct loop *
tree_unswitch_loop (struct loops *loops, struct loop *loop,
basic_block unswitch_on, tree cond)
{
basic_block condition_bb;
/* Some sanity checking. */
gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on));
gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2);
gcc_assert (loop->inner == NULL);
return loop_version (loops, loop, unshare_expr (cond),
&condition_bb, false);
}