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freebsd-dev/contrib/gcc/tree-ssa-propagate.c
Alexander Kabaev 6b834ef156 GCC 4.2.0 release.
2007-05-19 01:19:51 +00:00

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/* Generic SSA value propagation engine.
Copyright (C) 2004, 2005, 2006 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 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 "flags.h"
#include "rtl.h"
#include "tm_p.h"
#include "ggc.h"
#include "basic-block.h"
#include "output.h"
#include "expr.h"
#include "function.h"
#include "diagnostic.h"
#include "timevar.h"
#include "tree-dump.h"
#include "tree-flow.h"
#include "tree-pass.h"
#include "tree-ssa-propagate.h"
#include "langhooks.h"
#include "varray.h"
#include "vec.h"
/* This file implements a generic value propagation engine based on
the same propagation used by the SSA-CCP algorithm [1].
Propagation is performed by simulating the execution of every
statement that produces the value being propagated. Simulation
proceeds as follows:
1- Initially, all edges of the CFG are marked not executable and
the CFG worklist is seeded with all the statements in the entry
basic block (block 0).
2- Every statement S is simulated with a call to the call-back
function SSA_PROP_VISIT_STMT. This evaluation may produce 3
results:
SSA_PROP_NOT_INTERESTING: Statement S produces nothing of
interest and does not affect any of the work lists.
SSA_PROP_VARYING: The value produced by S cannot be determined
at compile time. Further simulation of S is not required.
If S is a conditional jump, all the outgoing edges for the
block are considered executable and added to the work
list.
SSA_PROP_INTERESTING: S produces a value that can be computed
at compile time. Its result can be propagated into the
statements that feed from S. Furthermore, if S is a
conditional jump, only the edge known to be taken is added
to the work list. Edges that are known not to execute are
never simulated.
3- PHI nodes are simulated with a call to SSA_PROP_VISIT_PHI. The
return value from SSA_PROP_VISIT_PHI has the same semantics as
described in #2.
4- Three work lists are kept. Statements are only added to these
lists if they produce one of SSA_PROP_INTERESTING or
SSA_PROP_VARYING.
CFG_BLOCKS contains the list of blocks to be simulated.
Blocks are added to this list if their incoming edges are
found executable.
VARYING_SSA_EDGES contains the list of statements that feed
from statements that produce an SSA_PROP_VARYING result.
These are simulated first to speed up processing.
INTERESTING_SSA_EDGES contains the list of statements that
feed from statements that produce an SSA_PROP_INTERESTING
result.
5- Simulation terminates when all three work lists are drained.
Before calling ssa_propagate, it is important to clear
DONT_SIMULATE_AGAIN for all the statements in the program that
should be simulated. This initialization allows an implementation
to specify which statements should never be simulated.
It is also important to compute def-use information before calling
ssa_propagate.
References:
[1] Constant propagation with conditional branches,
Wegman and Zadeck, ACM TOPLAS 13(2):181-210.
[2] Building an Optimizing Compiler,
Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
[3] Advanced Compiler Design and Implementation,
Steven Muchnick, Morgan Kaufmann, 1997, Section 12.6 */
/* Function pointers used to parameterize the propagation engine. */
static ssa_prop_visit_stmt_fn ssa_prop_visit_stmt;
static ssa_prop_visit_phi_fn ssa_prop_visit_phi;
/* Use the TREE_DEPRECATED bitflag to mark statements that have been
added to one of the SSA edges worklists. This flag is used to
avoid visiting statements unnecessarily when draining an SSA edge
worklist. If while simulating a basic block, we find a statement with
STMT_IN_SSA_EDGE_WORKLIST set, we clear it to prevent SSA edge
processing from visiting it again. */
#define STMT_IN_SSA_EDGE_WORKLIST(T) TREE_DEPRECATED (T)
/* A bitmap to keep track of executable blocks in the CFG. */
static sbitmap executable_blocks;
/* Array of control flow edges on the worklist. */
static VEC(basic_block,heap) *cfg_blocks;
static unsigned int cfg_blocks_num = 0;
static int cfg_blocks_tail;
static int cfg_blocks_head;
static sbitmap bb_in_list;
/* Worklist of SSA edges which will need reexamination as their
definition has changed. SSA edges are def-use edges in the SSA
web. For each D-U edge, we store the target statement or PHI node
U. */
static GTY(()) VEC(tree,gc) *interesting_ssa_edges;
/* Identical to INTERESTING_SSA_EDGES. For performance reasons, the
list of SSA edges is split into two. One contains all SSA edges
who need to be reexamined because their lattice value changed to
varying (this worklist), and the other contains all other SSA edges
to be reexamined (INTERESTING_SSA_EDGES).
Since most values in the program are VARYING, the ideal situation
is to move them to that lattice value as quickly as possible.
Thus, it doesn't make sense to process any other type of lattice
value until all VARYING values are propagated fully, which is one
thing using the VARYING worklist achieves. In addition, if we
don't use a separate worklist for VARYING edges, we end up with
situations where lattice values move from
UNDEFINED->INTERESTING->VARYING instead of UNDEFINED->VARYING. */
static GTY(()) VEC(tree,gc) *varying_ssa_edges;
/* Return true if the block worklist empty. */
static inline bool
cfg_blocks_empty_p (void)
{
return (cfg_blocks_num == 0);
}
/* Add a basic block to the worklist. The block must not be already
in the worklist, and it must not be the ENTRY or EXIT block. */
static void
cfg_blocks_add (basic_block bb)
{
gcc_assert (bb != ENTRY_BLOCK_PTR && bb != EXIT_BLOCK_PTR);
gcc_assert (!TEST_BIT (bb_in_list, bb->index));
if (cfg_blocks_empty_p ())
{
cfg_blocks_tail = cfg_blocks_head = 0;
cfg_blocks_num = 1;
}
else
{
cfg_blocks_num++;
if (cfg_blocks_num > VEC_length (basic_block, cfg_blocks))
{
/* We have to grow the array now. Adjust to queue to occupy
the full space of the original array. We do not need to
initialize the newly allocated portion of the array
because we keep track of CFG_BLOCKS_HEAD and
CFG_BLOCKS_HEAD. */
cfg_blocks_tail = VEC_length (basic_block, cfg_blocks);
cfg_blocks_head = 0;
VEC_safe_grow (basic_block, heap, cfg_blocks, 2 * cfg_blocks_tail);
}
else
cfg_blocks_tail = ((cfg_blocks_tail + 1)
% VEC_length (basic_block, cfg_blocks));
}
VEC_replace (basic_block, cfg_blocks, cfg_blocks_tail, bb);
SET_BIT (bb_in_list, bb->index);
}
/* Remove a block from the worklist. */
static basic_block
cfg_blocks_get (void)
{
basic_block bb;
bb = VEC_index (basic_block, cfg_blocks, cfg_blocks_head);
gcc_assert (!cfg_blocks_empty_p ());
gcc_assert (bb);
cfg_blocks_head = ((cfg_blocks_head + 1)
% VEC_length (basic_block, cfg_blocks));
--cfg_blocks_num;
RESET_BIT (bb_in_list, bb->index);
return bb;
}
/* We have just defined a new value for VAR. If IS_VARYING is true,
add all immediate uses of VAR to VARYING_SSA_EDGES, otherwise add
them to INTERESTING_SSA_EDGES. */
static void
add_ssa_edge (tree var, bool is_varying)
{
imm_use_iterator iter;
use_operand_p use_p;
FOR_EACH_IMM_USE_FAST (use_p, iter, var)
{
tree use_stmt = USE_STMT (use_p);
if (!DONT_SIMULATE_AGAIN (use_stmt)
&& !STMT_IN_SSA_EDGE_WORKLIST (use_stmt))
{
STMT_IN_SSA_EDGE_WORKLIST (use_stmt) = 1;
if (is_varying)
VEC_safe_push (tree, gc, varying_ssa_edges, use_stmt);
else
VEC_safe_push (tree, gc, interesting_ssa_edges, use_stmt);
}
}
}
/* Add edge E to the control flow worklist. */
static void
add_control_edge (edge e)
{
basic_block bb = e->dest;
if (bb == EXIT_BLOCK_PTR)
return;
/* If the edge had already been executed, skip it. */
if (e->flags & EDGE_EXECUTABLE)
return;
e->flags |= EDGE_EXECUTABLE;
/* If the block is already in the list, we're done. */
if (TEST_BIT (bb_in_list, bb->index))
return;
cfg_blocks_add (bb);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "Adding Destination of edge (%d -> %d) to worklist\n\n",
e->src->index, e->dest->index);
}
/* Simulate the execution of STMT and update the work lists accordingly. */
static void
simulate_stmt (tree stmt)
{
enum ssa_prop_result val = SSA_PROP_NOT_INTERESTING;
edge taken_edge = NULL;
tree output_name = NULL_TREE;
/* Don't bother visiting statements that are already
considered varying by the propagator. */
if (DONT_SIMULATE_AGAIN (stmt))
return;
if (TREE_CODE (stmt) == PHI_NODE)
{
val = ssa_prop_visit_phi (stmt);
output_name = PHI_RESULT (stmt);
}
else
val = ssa_prop_visit_stmt (stmt, &taken_edge, &output_name);
if (val == SSA_PROP_VARYING)
{
DONT_SIMULATE_AGAIN (stmt) = 1;
/* If the statement produced a new varying value, add the SSA
edges coming out of OUTPUT_NAME. */
if (output_name)
add_ssa_edge (output_name, true);
/* If STMT transfers control out of its basic block, add
all outgoing edges to the work list. */
if (stmt_ends_bb_p (stmt))
{
edge e;
edge_iterator ei;
basic_block bb = bb_for_stmt (stmt);
FOR_EACH_EDGE (e, ei, bb->succs)
add_control_edge (e);
}
}
else if (val == SSA_PROP_INTERESTING)
{
/* If the statement produced new value, add the SSA edges coming
out of OUTPUT_NAME. */
if (output_name)
add_ssa_edge (output_name, false);
/* If we know which edge is going to be taken out of this block,
add it to the CFG work list. */
if (taken_edge)
add_control_edge (taken_edge);
}
}
/* Process an SSA edge worklist. WORKLIST is the SSA edge worklist to
drain. This pops statements off the given WORKLIST and processes
them until there are no more statements on WORKLIST.
We take a pointer to WORKLIST because it may be reallocated when an
SSA edge is added to it in simulate_stmt. */
static void
process_ssa_edge_worklist (VEC(tree,gc) **worklist)
{
/* Drain the entire worklist. */
while (VEC_length (tree, *worklist) > 0)
{
basic_block bb;
/* Pull the statement to simulate off the worklist. */
tree stmt = VEC_pop (tree, *worklist);
/* If this statement was already visited by simulate_block, then
we don't need to visit it again here. */
if (!STMT_IN_SSA_EDGE_WORKLIST (stmt))
continue;
/* STMT is no longer in a worklist. */
STMT_IN_SSA_EDGE_WORKLIST (stmt) = 0;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "\nSimulating statement (from ssa_edges): ");
print_generic_stmt (dump_file, stmt, dump_flags);
}
bb = bb_for_stmt (stmt);
/* PHI nodes are always visited, regardless of whether or not
the destination block is executable. Otherwise, visit the
statement only if its block is marked executable. */
if (TREE_CODE (stmt) == PHI_NODE
|| TEST_BIT (executable_blocks, bb->index))
simulate_stmt (stmt);
}
}
/* Simulate the execution of BLOCK. Evaluate the statement associated
with each variable reference inside the block. */
static void
simulate_block (basic_block block)
{
tree phi;
/* There is nothing to do for the exit block. */
if (block == EXIT_BLOCK_PTR)
return;
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "\nSimulating block %d\n", block->index);
/* Always simulate PHI nodes, even if we have simulated this block
before. */
for (phi = phi_nodes (block); phi; phi = PHI_CHAIN (phi))
simulate_stmt (phi);
/* If this is the first time we've simulated this block, then we
must simulate each of its statements. */
if (!TEST_BIT (executable_blocks, block->index))
{
block_stmt_iterator j;
unsigned int normal_edge_count;
edge e, normal_edge;
edge_iterator ei;
/* Note that we have simulated this block. */
SET_BIT (executable_blocks, block->index);
for (j = bsi_start (block); !bsi_end_p (j); bsi_next (&j))
{
tree stmt = bsi_stmt (j);
/* If this statement is already in the worklist then
"cancel" it. The reevaluation implied by the worklist
entry will produce the same value we generate here and
thus reevaluating it again from the worklist is
pointless. */
if (STMT_IN_SSA_EDGE_WORKLIST (stmt))
STMT_IN_SSA_EDGE_WORKLIST (stmt) = 0;
simulate_stmt (stmt);
}
/* We can not predict when abnormal edges will be executed, so
once a block is considered executable, we consider any
outgoing abnormal edges as executable.
At the same time, if this block has only one successor that is
reached by non-abnormal edges, then add that successor to the
worklist. */
normal_edge_count = 0;
normal_edge = NULL;
FOR_EACH_EDGE (e, ei, block->succs)
{
if (e->flags & EDGE_ABNORMAL)
add_control_edge (e);
else
{
normal_edge_count++;
normal_edge = e;
}
}
if (normal_edge_count == 1)
add_control_edge (normal_edge);
}
}
/* Initialize local data structures and work lists. */
static void
ssa_prop_init (void)
{
edge e;
edge_iterator ei;
basic_block bb;
size_t i;
/* Worklists of SSA edges. */
interesting_ssa_edges = VEC_alloc (tree, gc, 20);
varying_ssa_edges = VEC_alloc (tree, gc, 20);
executable_blocks = sbitmap_alloc (last_basic_block);
sbitmap_zero (executable_blocks);
bb_in_list = sbitmap_alloc (last_basic_block);
sbitmap_zero (bb_in_list);
if (dump_file && (dump_flags & TDF_DETAILS))
dump_immediate_uses (dump_file);
cfg_blocks = VEC_alloc (basic_block, heap, 20);
VEC_safe_grow (basic_block, heap, cfg_blocks, 20);
/* Initialize the values for every SSA_NAME. */
for (i = 1; i < num_ssa_names; i++)
if (ssa_name (i))
SSA_NAME_VALUE (ssa_name (i)) = NULL_TREE;
/* Initially assume that every edge in the CFG is not executable.
(including the edges coming out of ENTRY_BLOCK_PTR). */
FOR_ALL_BB (bb)
{
block_stmt_iterator si;
for (si = bsi_start (bb); !bsi_end_p (si); bsi_next (&si))
STMT_IN_SSA_EDGE_WORKLIST (bsi_stmt (si)) = 0;
FOR_EACH_EDGE (e, ei, bb->succs)
e->flags &= ~EDGE_EXECUTABLE;
}
/* Seed the algorithm by adding the successors of the entry block to the
edge worklist. */
FOR_EACH_EDGE (e, ei, ENTRY_BLOCK_PTR->succs)
add_control_edge (e);
}
/* Free allocated storage. */
static void
ssa_prop_fini (void)
{
VEC_free (tree, gc, interesting_ssa_edges);
VEC_free (tree, gc, varying_ssa_edges);
VEC_free (basic_block, heap, cfg_blocks);
cfg_blocks = NULL;
sbitmap_free (bb_in_list);
sbitmap_free (executable_blocks);
}
/* Get the main expression from statement STMT. */
tree
get_rhs (tree stmt)
{
enum tree_code code = TREE_CODE (stmt);
switch (code)
{
case RETURN_EXPR:
stmt = TREE_OPERAND (stmt, 0);
if (!stmt || TREE_CODE (stmt) != MODIFY_EXPR)
return stmt;
/* FALLTHRU */
case MODIFY_EXPR:
stmt = TREE_OPERAND (stmt, 1);
if (TREE_CODE (stmt) == WITH_SIZE_EXPR)
return TREE_OPERAND (stmt, 0);
else
return stmt;
case COND_EXPR:
return COND_EXPR_COND (stmt);
case SWITCH_EXPR:
return SWITCH_COND (stmt);
case GOTO_EXPR:
return GOTO_DESTINATION (stmt);
case LABEL_EXPR:
return LABEL_EXPR_LABEL (stmt);
default:
return stmt;
}
}
/* Set the main expression of *STMT_P to EXPR. If EXPR is not a valid
GIMPLE expression no changes are done and the function returns
false. */
bool
set_rhs (tree *stmt_p, tree expr)
{
tree stmt = *stmt_p, op;
enum tree_code code = TREE_CODE (expr);
stmt_ann_t ann;
tree var;
ssa_op_iter iter;
/* Verify the constant folded result is valid gimple. */
if (TREE_CODE_CLASS (code) == tcc_binary)
{
if (!is_gimple_val (TREE_OPERAND (expr, 0))
|| !is_gimple_val (TREE_OPERAND (expr, 1)))
return false;
}
else if (TREE_CODE_CLASS (code) == tcc_unary)
{
if (!is_gimple_val (TREE_OPERAND (expr, 0)))
return false;
}
else if (code == ADDR_EXPR)
{
if (TREE_CODE (TREE_OPERAND (expr, 0)) == ARRAY_REF
&& !is_gimple_val (TREE_OPERAND (TREE_OPERAND (expr, 0), 1)))
return false;
}
else if (code == COMPOUND_EXPR
|| code == MODIFY_EXPR)
return false;
if (EXPR_HAS_LOCATION (stmt)
&& EXPR_P (expr)
&& ! EXPR_HAS_LOCATION (expr)
&& TREE_SIDE_EFFECTS (expr)
&& TREE_CODE (expr) != LABEL_EXPR)
SET_EXPR_LOCATION (expr, EXPR_LOCATION (stmt));
switch (TREE_CODE (stmt))
{
case RETURN_EXPR:
op = TREE_OPERAND (stmt, 0);
if (TREE_CODE (op) != MODIFY_EXPR)
{
TREE_OPERAND (stmt, 0) = expr;
break;
}
stmt = op;
/* FALLTHRU */
case MODIFY_EXPR:
op = TREE_OPERAND (stmt, 1);
if (TREE_CODE (op) == WITH_SIZE_EXPR)
stmt = op;
TREE_OPERAND (stmt, 1) = expr;
break;
case COND_EXPR:
if (!is_gimple_condexpr (expr))
return false;
COND_EXPR_COND (stmt) = expr;
break;
case SWITCH_EXPR:
SWITCH_COND (stmt) = expr;
break;
case GOTO_EXPR:
GOTO_DESTINATION (stmt) = expr;
break;
case LABEL_EXPR:
LABEL_EXPR_LABEL (stmt) = expr;
break;
default:
/* Replace the whole statement with EXPR. If EXPR has no side
effects, then replace *STMT_P with an empty statement. */
ann = stmt_ann (stmt);
*stmt_p = TREE_SIDE_EFFECTS (expr) ? expr : build_empty_stmt ();
(*stmt_p)->common.ann = (tree_ann_t) ann;
if (in_ssa_p
&& TREE_SIDE_EFFECTS (expr))
{
/* Fix all the SSA_NAMEs created by *STMT_P to point to its new
replacement. */
FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_ALL_DEFS)
{
if (TREE_CODE (var) == SSA_NAME)
SSA_NAME_DEF_STMT (var) = *stmt_p;
}
}
break;
}
return true;
}
/* Entry point to the propagation engine.
VISIT_STMT is called for every statement visited.
VISIT_PHI is called for every PHI node visited. */
void
ssa_propagate (ssa_prop_visit_stmt_fn visit_stmt,
ssa_prop_visit_phi_fn visit_phi)
{
ssa_prop_visit_stmt = visit_stmt;
ssa_prop_visit_phi = visit_phi;
ssa_prop_init ();
/* Iterate until the worklists are empty. */
while (!cfg_blocks_empty_p ()
|| VEC_length (tree, interesting_ssa_edges) > 0
|| VEC_length (tree, varying_ssa_edges) > 0)
{
if (!cfg_blocks_empty_p ())
{
/* Pull the next block to simulate off the worklist. */
basic_block dest_block = cfg_blocks_get ();
simulate_block (dest_block);
}
/* In order to move things to varying as quickly as
possible,process the VARYING_SSA_EDGES worklist first. */
process_ssa_edge_worklist (&varying_ssa_edges);
/* Now process the INTERESTING_SSA_EDGES worklist. */
process_ssa_edge_worklist (&interesting_ssa_edges);
}
ssa_prop_fini ();
}
/* Return the first V_MAY_DEF or V_MUST_DEF operand for STMT. */
tree
first_vdef (tree stmt)
{
ssa_op_iter iter;
tree op;
/* Simply return the first operand we arrive at. */
FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_VIRTUAL_DEFS)
return (op);
gcc_unreachable ();
}
/* Return true if STMT is of the form 'LHS = mem_ref', where 'mem_ref'
is a non-volatile pointer dereference, a structure reference or a
reference to a single _DECL. Ignore volatile memory references
because they are not interesting for the optimizers. */
bool
stmt_makes_single_load (tree stmt)
{
tree rhs;
if (TREE_CODE (stmt) != MODIFY_EXPR)
return false;
if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VMAYDEF|SSA_OP_VUSE))
return false;
rhs = TREE_OPERAND (stmt, 1);
STRIP_NOPS (rhs);
return (!TREE_THIS_VOLATILE (rhs)
&& (DECL_P (rhs)
|| REFERENCE_CLASS_P (rhs)));
}
/* Return true if STMT is of the form 'mem_ref = RHS', where 'mem_ref'
is a non-volatile pointer dereference, a structure reference or a
reference to a single _DECL. Ignore volatile memory references
because they are not interesting for the optimizers. */
bool
stmt_makes_single_store (tree stmt)
{
tree lhs;
if (TREE_CODE (stmt) != MODIFY_EXPR)
return false;
if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VMAYDEF|SSA_OP_VMUSTDEF))
return false;
lhs = TREE_OPERAND (stmt, 0);
STRIP_NOPS (lhs);
return (!TREE_THIS_VOLATILE (lhs)
&& (DECL_P (lhs)
|| REFERENCE_CLASS_P (lhs)));
}
/* If STMT makes a single memory load and all the virtual use operands
have the same value in array VALUES, return it. Otherwise, return
NULL. */
prop_value_t *
get_value_loaded_by (tree stmt, prop_value_t *values)
{
ssa_op_iter i;
tree vuse;
prop_value_t *prev_val = NULL;
prop_value_t *val = NULL;
FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, i, SSA_OP_VIRTUAL_USES)
{
val = &values[SSA_NAME_VERSION (vuse)];
if (prev_val && prev_val->value != val->value)
return NULL;
prev_val = val;
}
return val;
}
/* Propagation statistics. */
struct prop_stats_d
{
long num_const_prop;
long num_copy_prop;
long num_pred_folded;
};
static struct prop_stats_d prop_stats;
/* Replace USE references in statement STMT with the values stored in
PROP_VALUE. Return true if at least one reference was replaced. If
REPLACED_ADDRESSES_P is given, it will be set to true if an address
constant was replaced. */
bool
replace_uses_in (tree stmt, bool *replaced_addresses_p,
prop_value_t *prop_value)
{
bool replaced = false;
use_operand_p use;
ssa_op_iter iter;
FOR_EACH_SSA_USE_OPERAND (use, stmt, iter, SSA_OP_USE)
{
tree tuse = USE_FROM_PTR (use);
tree val = prop_value[SSA_NAME_VERSION (tuse)].value;
if (val == tuse || val == NULL_TREE)
continue;
if (TREE_CODE (stmt) == ASM_EXPR
&& !may_propagate_copy_into_asm (tuse))
continue;
if (!may_propagate_copy (tuse, val))
continue;
if (TREE_CODE (val) != SSA_NAME)
prop_stats.num_const_prop++;
else
prop_stats.num_copy_prop++;
propagate_value (use, val);
replaced = true;
if (POINTER_TYPE_P (TREE_TYPE (tuse)) && replaced_addresses_p)
*replaced_addresses_p = true;
}
return replaced;
}
/* Replace the VUSE references in statement STMT with the values
stored in PROP_VALUE. Return true if a reference was replaced. If
REPLACED_ADDRESSES_P is given, it will be set to true if an address
constant was replaced.
Replacing VUSE operands is slightly more complex than replacing
regular USEs. We are only interested in two types of replacements
here:
1- If the value to be replaced is a constant or an SSA name for a
GIMPLE register, then we are making a copy/constant propagation
from a memory store. For instance,
# a_3 = V_MAY_DEF <a_2>
a.b = x_1;
...
# VUSE <a_3>
y_4 = a.b;
This replacement is only possible iff STMT is an assignment
whose RHS is identical to the LHS of the statement that created
the VUSE(s) that we are replacing. Otherwise, we may do the
wrong replacement:
# a_3 = V_MAY_DEF <a_2>
# b_5 = V_MAY_DEF <b_4>
*p = 10;
...
# VUSE <b_5>
x_8 = b;
Even though 'b_5' acquires the value '10' during propagation,
there is no way for the propagator to tell whether the
replacement is correct in every reached use, because values are
computed at definition sites. Therefore, when doing final
substitution of propagated values, we have to check each use
site. Since the RHS of STMT ('b') is different from the LHS of
the originating statement ('*p'), we cannot replace 'b' with
'10'.
Similarly, when merging values from PHI node arguments,
propagators need to take care not to merge the same values
stored in different locations:
if (...)
# a_3 = V_MAY_DEF <a_2>
a.b = 3;
else
# a_4 = V_MAY_DEF <a_2>
a.c = 3;
# a_5 = PHI <a_3, a_4>
It would be wrong to propagate '3' into 'a_5' because that
operation merges two stores to different memory locations.
2- If the value to be replaced is an SSA name for a virtual
register, then we simply replace each VUSE operand with its
value from PROP_VALUE. This is the same replacement done by
replace_uses_in. */
static bool
replace_vuses_in (tree stmt, bool *replaced_addresses_p,
prop_value_t *prop_value)
{
bool replaced = false;
ssa_op_iter iter;
use_operand_p vuse;
if (stmt_makes_single_load (stmt))
{
/* If STMT is an assignment whose RHS is a single memory load,
see if we are trying to propagate a constant or a GIMPLE
register (case #1 above). */
prop_value_t *val = get_value_loaded_by (stmt, prop_value);
tree rhs = TREE_OPERAND (stmt, 1);
if (val
&& val->value
&& (is_gimple_reg (val->value)
|| is_gimple_min_invariant (val->value))
&& simple_cst_equal (rhs, val->mem_ref) == 1)
{
/* If we are replacing a constant address, inform our
caller. */
if (TREE_CODE (val->value) != SSA_NAME
&& POINTER_TYPE_P (TREE_TYPE (TREE_OPERAND (stmt, 1)))
&& replaced_addresses_p)
*replaced_addresses_p = true;
/* We can only perform the substitution if the load is done
from the same memory location as the original store.
Since we already know that there are no intervening
stores between DEF_STMT and STMT, we only need to check
that the RHS of STMT is the same as the memory reference
propagated together with the value. */
TREE_OPERAND (stmt, 1) = val->value;
if (TREE_CODE (val->value) != SSA_NAME)
prop_stats.num_const_prop++;
else
prop_stats.num_copy_prop++;
/* Since we have replaced the whole RHS of STMT, there
is no point in checking the other VUSEs, as they will
all have the same value. */
return true;
}
}
/* Otherwise, the values for every VUSE operand must be other
SSA_NAMEs that can be propagated into STMT. */
FOR_EACH_SSA_USE_OPERAND (vuse, stmt, iter, SSA_OP_VIRTUAL_USES)
{
tree var = USE_FROM_PTR (vuse);
tree val = prop_value[SSA_NAME_VERSION (var)].value;
if (val == NULL_TREE || var == val)
continue;
/* Constants and copies propagated between real and virtual
operands are only possible in the cases handled above. They
should be ignored in any other context. */
if (is_gimple_min_invariant (val) || is_gimple_reg (val))
continue;
propagate_value (vuse, val);
prop_stats.num_copy_prop++;
replaced = true;
}
return replaced;
}
/* Replace propagated values into all the arguments for PHI using the
values from PROP_VALUE. */
static void
replace_phi_args_in (tree phi, prop_value_t *prop_value)
{
int i;
bool replaced = false;
tree prev_phi = NULL;
if (dump_file && (dump_flags & TDF_DETAILS))
prev_phi = unshare_expr (phi);
for (i = 0; i < PHI_NUM_ARGS (phi); i++)
{
tree arg = PHI_ARG_DEF (phi, i);
if (TREE_CODE (arg) == SSA_NAME)
{
tree val = prop_value[SSA_NAME_VERSION (arg)].value;
if (val && val != arg && may_propagate_copy (arg, val))
{
if (TREE_CODE (val) != SSA_NAME)
prop_stats.num_const_prop++;
else
prop_stats.num_copy_prop++;
propagate_value (PHI_ARG_DEF_PTR (phi, i), val);
replaced = true;
/* If we propagated a copy and this argument flows
through an abnormal edge, update the replacement
accordingly. */
if (TREE_CODE (val) == SSA_NAME
&& PHI_ARG_EDGE (phi, i)->flags & EDGE_ABNORMAL)
SSA_NAME_OCCURS_IN_ABNORMAL_PHI (val) = 1;
}
}
}
if (replaced && dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Folded PHI node: ");
print_generic_stmt (dump_file, prev_phi, TDF_SLIM);
fprintf (dump_file, " into: ");
print_generic_stmt (dump_file, phi, TDF_SLIM);
fprintf (dump_file, "\n");
}
}
/* If STMT has a predicate whose value can be computed using the value
range information computed by VRP, compute its value and return true.
Otherwise, return false. */
static bool
fold_predicate_in (tree stmt)
{
tree *pred_p = NULL;
bool modify_expr_p = false;
tree val;
if (TREE_CODE (stmt) == MODIFY_EXPR
&& COMPARISON_CLASS_P (TREE_OPERAND (stmt, 1)))
{
modify_expr_p = true;
pred_p = &TREE_OPERAND (stmt, 1);
}
else if (TREE_CODE (stmt) == COND_EXPR)
pred_p = &COND_EXPR_COND (stmt);
else
return false;
val = vrp_evaluate_conditional (*pred_p, stmt);
if (val)
{
if (modify_expr_p)
val = fold_convert (TREE_TYPE (*pred_p), val);
if (dump_file)
{
fprintf (dump_file, "Folding predicate ");
print_generic_expr (dump_file, *pred_p, 0);
fprintf (dump_file, " to ");
print_generic_expr (dump_file, val, 0);
fprintf (dump_file, "\n");
}
prop_stats.num_pred_folded++;
*pred_p = val;
return true;
}
return false;
}
/* Perform final substitution and folding of propagated values.
PROP_VALUE[I] contains the single value that should be substituted
at every use of SSA name N_I. If PROP_VALUE is NULL, no values are
substituted.
If USE_RANGES_P is true, statements that contain predicate
expressions are evaluated with a call to vrp_evaluate_conditional.
This will only give meaningful results when called from tree-vrp.c
(the information used by vrp_evaluate_conditional is built by the
VRP pass). */
void
substitute_and_fold (prop_value_t *prop_value, bool use_ranges_p)
{
basic_block bb;
if (prop_value == NULL && !use_ranges_p)
return;
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "\nSubstituing values and folding statements\n\n");
memset (&prop_stats, 0, sizeof (prop_stats));
/* Substitute values in every statement of every basic block. */
FOR_EACH_BB (bb)
{
block_stmt_iterator i;
tree phi;
/* Propagate known values into PHI nodes. */
if (prop_value)
for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
replace_phi_args_in (phi, prop_value);
for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
{
bool replaced_address, did_replace;
tree prev_stmt = NULL;
tree stmt = bsi_stmt (i);
/* Ignore ASSERT_EXPRs. They are used by VRP to generate
range information for names and they are discarded
afterwards. */
if (TREE_CODE (stmt) == MODIFY_EXPR
&& TREE_CODE (TREE_OPERAND (stmt, 1)) == ASSERT_EXPR)
continue;
/* Replace the statement with its folded version and mark it
folded. */
did_replace = false;
replaced_address = false;
if (dump_file && (dump_flags & TDF_DETAILS))
prev_stmt = unshare_expr (stmt);
/* If we have range information, see if we can fold
predicate expressions. */
if (use_ranges_p)
did_replace = fold_predicate_in (stmt);
if (prop_value)
{
/* Only replace real uses if we couldn't fold the
statement using value range information (value range
information is not collected on virtuals, so we only
need to check this for real uses). */
if (!did_replace)
did_replace |= replace_uses_in (stmt, &replaced_address,
prop_value);
did_replace |= replace_vuses_in (stmt, &replaced_address,
prop_value);
}
/* If we made a replacement, fold and cleanup the statement. */
if (did_replace)
{
tree old_stmt = stmt;
tree rhs;
fold_stmt (bsi_stmt_ptr (i));
stmt = bsi_stmt (i);
/* If we folded a builtin function, we'll likely
need to rename VDEFs. */
mark_new_vars_to_rename (stmt);
/* If we cleaned up EH information from the statement,
remove EH edges. */
if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt))
tree_purge_dead_eh_edges (bb);
rhs = get_rhs (stmt);
if (TREE_CODE (rhs) == ADDR_EXPR)
recompute_tree_invariant_for_addr_expr (rhs);
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Folded statement: ");
print_generic_stmt (dump_file, prev_stmt, TDF_SLIM);
fprintf (dump_file, " into: ");
print_generic_stmt (dump_file, stmt, TDF_SLIM);
fprintf (dump_file, "\n");
}
}
/* Some statements may be simplified using ranges. For
example, division may be replaced by shifts, modulo
replaced with bitwise and, etc. Do this after
substituting constants, folding, etc so that we're
presented with a fully propagated, canonicalized
statement. */
if (use_ranges_p)
simplify_stmt_using_ranges (stmt);
}
}
if (dump_file && (dump_flags & TDF_STATS))
{
fprintf (dump_file, "Constants propagated: %6ld\n",
prop_stats.num_const_prop);
fprintf (dump_file, "Copies propagated: %6ld\n",
prop_stats.num_copy_prop);
fprintf (dump_file, "Predicates folded: %6ld\n",
prop_stats.num_pred_folded);
}
}
#include "gt-tree-ssa-propagate.h"
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