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| Current File : //usr/src/contrib/gcc/ipa-pure-const.c |
/* Callgraph based analysis of static variables.
Copyright (C) 2004, 2005 Free Software Foundation, Inc.
Contributed by Kenneth Zadeck <zadeck@naturalbridge.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. */
/* This file mark functions as being either const (TREE_READONLY) or
pure (DECL_IS_PURE).
This must be run after inlining decisions have been made since
otherwise, the local sets will not contain information that is
consistent with post inlined state. The global sets are not prone
to this problem since they are by definition transitive. */
/* The code in this module is called by the ipa pass manager. It
should be one of the later passes since it's information is used by
the rest of the compilation. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "tree-flow.h"
#include "tree-inline.h"
#include "tree-pass.h"
#include "langhooks.h"
#include "pointer-set.h"
#include "ggc.h"
#include "ipa-utils.h"
#include "c-common.h"
#include "tree-gimple.h"
#include "cgraph.h"
#include "output.h"
#include "flags.h"
#include "timevar.h"
#include "diagnostic.h"
#include "langhooks.h"
#include "target.h"
static struct pointer_set_t *visited_nodes;
/* Lattice values for const and pure functions. Everything starts out
being const, then may drop to pure and then neither depending on
what is found. */
enum pure_const_state_e
{
IPA_CONST,
IPA_PURE,
IPA_NEITHER
};
/* Holder inserted into the ipa_dfs_info aux field to hold the
const_state. */
struct funct_state_d
{
enum pure_const_state_e pure_const_state;
bool state_set_in_source;
};
typedef struct funct_state_d * funct_state;
/* Return the function state from NODE. */
static inline funct_state
get_function_state (struct cgraph_node *node)
{
struct ipa_dfs_info * info = node->aux;
return info->aux;
}
/* Check to see if the use (or definition when CHECHING_WRITE is true)
variable T is legal in a function that is either pure or const. */
static inline void
check_decl (funct_state local,
tree t, bool checking_write)
{
/* If the variable has the "used" attribute, treat it as if it had a
been touched by the devil. */
if (lookup_attribute ("used", DECL_ATTRIBUTES (t)))
{
local->pure_const_state = IPA_NEITHER;
return;
}
/* Do not want to do anything with volatile except mark any
function that uses one to be not const or pure. */
if (TREE_THIS_VOLATILE (t))
{
local->pure_const_state = IPA_NEITHER;
return;
}
/* Do not care about a local automatic that is not static. */
if (!TREE_STATIC (t) && !DECL_EXTERNAL (t))
return;
/* Since we have dealt with the locals and params cases above, if we
are CHECKING_WRITE, this cannot be a pure or constant
function. */
if (checking_write)
local->pure_const_state = IPA_NEITHER;
if (DECL_EXTERNAL (t) || TREE_PUBLIC (t))
{
/* If the front end set the variable to be READONLY and
constant, we can allow this variable in pure or const
functions but the scope is too large for our analysis to set
these bits ourselves. */
if (TREE_READONLY (t)
&& DECL_INITIAL (t)
&& is_gimple_min_invariant (DECL_INITIAL (t)))
; /* Read of a constant, do not change the function state. */
else
{
/* Just a regular read. */
if (local->pure_const_state == IPA_CONST)
local->pure_const_state = IPA_PURE;
}
}
/* Compilation level statics can be read if they are readonly
variables. */
if (TREE_READONLY (t))
return;
/* Just a regular read. */
if (local->pure_const_state == IPA_CONST)
local->pure_const_state = IPA_PURE;
}
/* If T is a VAR_DECL check to see if it is an allowed reference. */
static void
check_operand (funct_state local,
tree t, bool checking_write)
{
if (!t) return;
if (TREE_CODE (t) == VAR_DECL)
check_decl (local, t, checking_write);
}
/* Examine tree T for references. */
static void
check_tree (funct_state local, tree t, bool checking_write)
{
if ((TREE_CODE (t) == EXC_PTR_EXPR) || (TREE_CODE (t) == FILTER_EXPR))
return;
/* Any tree which is volatile disqualifies thie function from being
const or pure. */
if (TREE_THIS_VOLATILE (t))
{
local->pure_const_state = IPA_NEITHER;
return;
}
while (TREE_CODE (t) == REALPART_EXPR
|| TREE_CODE (t) == IMAGPART_EXPR
|| handled_component_p (t))
{
if (TREE_CODE (t) == ARRAY_REF)
check_operand (local, TREE_OPERAND (t, 1), false);
t = TREE_OPERAND (t, 0);
}
/* The bottom of an indirect reference can only be read, not
written. */
if (INDIRECT_REF_P (t))
{
check_tree (local, TREE_OPERAND (t, 0), false);
/* Any indirect reference that occurs on the lhs
disqualifies the function from being pure or const. Any
indirect reference that occurs on the rhs disqualifies the
function from being const. */
if (checking_write)
{
local->pure_const_state = IPA_NEITHER;
return;
}
else if (local->pure_const_state == IPA_CONST)
local->pure_const_state = IPA_PURE;
}
if (SSA_VAR_P (t))
check_operand (local, t, checking_write);
}
/* Scan tree T to see if there are any addresses taken in within T. */
static void
look_for_address_of (funct_state local, tree t)
{
if (TREE_CODE (t) == ADDR_EXPR)
{
tree x = get_base_var (t);
if (TREE_CODE (x) == VAR_DECL)
{
check_decl (local, x, false);
/* Taking the address of something appears to be reasonable
in PURE code. Not allowed in const. */
if (local->pure_const_state == IPA_CONST)
local->pure_const_state = IPA_PURE;
}
}
}
/* Check to see if T is a read or address of operation on a var we are
interested in analyzing. LOCAL is passed in to get access to its
bit vectors. */
static void
check_rhs_var (funct_state local, tree t)
{
look_for_address_of (local, t);
/* Memcmp and strlen can both trap and they are declared pure. */
if (tree_could_trap_p (t)
&& local->pure_const_state == IPA_CONST)
local->pure_const_state = IPA_PURE;
check_tree(local, t, false);
}
/* Check to see if T is an assignment to a var we are interested in
analyzing. LOCAL is passed in to get access to its bit vectors. */
static void
check_lhs_var (funct_state local, tree t)
{
/* Memcmp and strlen can both trap and they are declared pure.
Which seems to imply that we can apply the same rule here. */
if (tree_could_trap_p (t)
&& local->pure_const_state == IPA_CONST)
local->pure_const_state = IPA_PURE;
check_tree(local, t, true);
}
/* This is a scaled down version of get_asm_expr_operands from
tree_ssa_operands.c. The version there runs much later and assumes
that aliasing information is already available. Here we are just
trying to find if the set of inputs and outputs contain references
or address of operations to local static variables. STMT is the
actual asm statement. */
static void
get_asm_expr_operands (funct_state local, tree stmt)
{
int noutputs = list_length (ASM_OUTPUTS (stmt));
const char **oconstraints
= (const char **) alloca ((noutputs) * sizeof (const char *));
int i;
tree link;
const char *constraint;
bool allows_mem, allows_reg, is_inout;
for (i=0, link = ASM_OUTPUTS (stmt); link; ++i, link = TREE_CHAIN (link))
{
oconstraints[i] = constraint
= TREE_STRING_POINTER (TREE_VALUE (TREE_PURPOSE (link)));
parse_output_constraint (&constraint, i, 0, 0,
&allows_mem, &allows_reg, &is_inout);
check_lhs_var (local, TREE_VALUE (link));
}
for (link = ASM_INPUTS (stmt); link; link = TREE_CHAIN (link))
{
constraint
= TREE_STRING_POINTER (TREE_VALUE (TREE_PURPOSE (link)));
parse_input_constraint (&constraint, 0, 0, noutputs, 0,
oconstraints, &allows_mem, &allows_reg);
check_rhs_var (local, TREE_VALUE (link));
}
for (link = ASM_CLOBBERS (stmt); link; link = TREE_CHAIN (link))
if (simple_cst_equal(TREE_VALUE (link), memory_identifier_string) == 1)
/* Abandon all hope, ye who enter here. */
local->pure_const_state = IPA_NEITHER;
if (ASM_VOLATILE_P (stmt))
local->pure_const_state = IPA_NEITHER;
}
/* Check the parameters of a function call to CALL_EXPR to see if
there are any references in the parameters that are not allowed for
pure or const functions. Also check to see if this is either an
indirect call, a call outside the compilation unit, or has special
attributes that may also effect the purity. The CALL_EXPR node for
the entire call expression. */
static void
check_call (funct_state local, tree call_expr)
{
int flags = call_expr_flags(call_expr);
tree operand_list = TREE_OPERAND (call_expr, 1);
tree operand;
tree callee_t = get_callee_fndecl (call_expr);
struct cgraph_node* callee;
enum availability avail = AVAIL_NOT_AVAILABLE;
for (operand = operand_list;
operand != NULL_TREE;
operand = TREE_CHAIN (operand))
{
tree argument = TREE_VALUE (operand);
check_rhs_var (local, argument);
}
/* The const and pure flags are set by a variety of places in the
compiler (including here). If someone has already set the flags
for the callee, (such as for some of the builtins) we will use
them, otherwise we will compute our own information.
Const and pure functions have less clobber effects than other
functions so we process these first. Otherwise if it is a call
outside the compilation unit or an indirect call we punt. This
leaves local calls which will be processed by following the call
graph. */
if (callee_t)
{
callee = cgraph_node(callee_t);
avail = cgraph_function_body_availability (callee);
/* When bad things happen to bad functions, they cannot be const
or pure. */
if (setjmp_call_p (callee_t))
local->pure_const_state = IPA_NEITHER;
if (DECL_BUILT_IN_CLASS (callee_t) == BUILT_IN_NORMAL)
switch (DECL_FUNCTION_CODE (callee_t))
{
case BUILT_IN_LONGJMP:
case BUILT_IN_NONLOCAL_GOTO:
local->pure_const_state = IPA_NEITHER;
break;
default:
break;
}
}
/* The callee is either unknown (indirect call) or there is just no
scannable code for it (external call) . We look to see if there
are any bits available for the callee (such as by declaration or
because it is builtin) and process solely on the basis of those
bits. */
if (avail == AVAIL_NOT_AVAILABLE || avail == AVAIL_OVERWRITABLE)
{
if (flags & ECF_PURE)
{
if (local->pure_const_state == IPA_CONST)
local->pure_const_state = IPA_PURE;
}
else
local->pure_const_state = IPA_NEITHER;
}
else
{
/* We have the code and we will scan it for the effects. */
if (flags & ECF_PURE)
{
if (local->pure_const_state == IPA_CONST)
local->pure_const_state = IPA_PURE;
}
}
}
/* TP is the part of the tree currently under the microscope.
WALK_SUBTREES is part of the walk_tree api but is unused here.
DATA is cgraph_node of the function being walked. */
/* FIXME: When this is converted to run over SSA form, this code
should be converted to use the operand scanner. */
static tree
scan_function (tree *tp,
int *walk_subtrees,
void *data)
{
struct cgraph_node *fn = data;
tree t = *tp;
funct_state local = get_function_state (fn);
switch (TREE_CODE (t))
{
case VAR_DECL:
if (DECL_INITIAL (t))
walk_tree (&DECL_INITIAL (t), scan_function, fn, visited_nodes);
*walk_subtrees = 0;
break;
case MODIFY_EXPR:
{
/* First look on the lhs and see what variable is stored to */
tree lhs = TREE_OPERAND (t, 0);
tree rhs = TREE_OPERAND (t, 1);
check_lhs_var (local, lhs);
/* For the purposes of figuring out what the cast affects */
/* Next check the operands on the rhs to see if they are ok. */
switch (TREE_CODE_CLASS (TREE_CODE (rhs)))
{
case tcc_binary:
{
tree op0 = TREE_OPERAND (rhs, 0);
tree op1 = TREE_OPERAND (rhs, 1);
check_rhs_var (local, op0);
check_rhs_var (local, op1);
}
break;
case tcc_unary:
{
tree op0 = TREE_OPERAND (rhs, 0);
check_rhs_var (local, op0);
}
break;
case tcc_reference:
check_rhs_var (local, rhs);
break;
case tcc_declaration:
check_rhs_var (local, rhs);
break;
case tcc_expression:
switch (TREE_CODE (rhs))
{
case ADDR_EXPR:
check_rhs_var (local, rhs);
break;
case CALL_EXPR:
check_call (local, rhs);
break;
default:
break;
}
break;
default:
break;
}
*walk_subtrees = 0;
}
break;
case ADDR_EXPR:
/* This case is here to find addresses on rhs of constructors in
decl_initial of static variables. */
check_rhs_var (local, t);
*walk_subtrees = 0;
break;
case LABEL_EXPR:
if (DECL_NONLOCAL (TREE_OPERAND (t, 0)))
/* Target of long jump. */
local->pure_const_state = IPA_NEITHER;
break;
case CALL_EXPR:
check_call (local, t);
*walk_subtrees = 0;
break;
case ASM_EXPR:
get_asm_expr_operands (local, t);
*walk_subtrees = 0;
break;
default:
break;
}
return NULL;
}
/* This is the main routine for finding the reference patterns for
global variables within a function FN. */
static void
analyze_function (struct cgraph_node *fn)
{
funct_state l = XCNEW (struct funct_state_d);
tree decl = fn->decl;
struct ipa_dfs_info * w_info = fn->aux;
w_info->aux = l;
l->pure_const_state = IPA_CONST;
l->state_set_in_source = false;
/* If this function does not return normally or does not bind local,
do not touch this unless it has been marked as const or pure by the
front end. */
if (TREE_THIS_VOLATILE (decl)
|| !targetm.binds_local_p (decl))
{
l->pure_const_state = IPA_NEITHER;
return;
}
if (TREE_READONLY (decl))
{
l->pure_const_state = IPA_CONST;
l->state_set_in_source = true;
}
if (DECL_IS_PURE (decl))
{
l->pure_const_state = IPA_PURE;
l->state_set_in_source = true;
}
if (dump_file)
{
fprintf (dump_file, "\n local analysis of %s with initial value = %d\n ",
cgraph_node_name (fn),
l->pure_const_state);
}
if (!l->state_set_in_source)
{
struct function *this_cfun = DECL_STRUCT_FUNCTION (decl);
basic_block this_block;
FOR_EACH_BB_FN (this_block, this_cfun)
{
block_stmt_iterator bsi;
for (bsi = bsi_start (this_block); !bsi_end_p (bsi); bsi_next (&bsi))
{
walk_tree (bsi_stmt_ptr (bsi), scan_function,
fn, visited_nodes);
if (l->pure_const_state == IPA_NEITHER)
goto end;
}
}
if (l->pure_const_state != IPA_NEITHER)
{
tree old_decl = current_function_decl;
/* Const functions cannot have back edges (an
indication of possible infinite loop side
effect. */
current_function_decl = fn->decl;
/* The C++ front end, has a tendency to some times jerk away
a function after it has created it. This should have
been fixed. */
gcc_assert (DECL_STRUCT_FUNCTION (fn->decl));
push_cfun (DECL_STRUCT_FUNCTION (fn->decl));
if (mark_dfs_back_edges ())
l->pure_const_state = IPA_NEITHER;
current_function_decl = old_decl;
pop_cfun ();
}
}
end:
if (dump_file)
{
fprintf (dump_file, "after local analysis of %s with initial value = %d\n ",
cgraph_node_name (fn),
l->pure_const_state);
}
}
/* Produce the global information by preforming a transitive closure
on the local information that was produced by ipa_analyze_function
and ipa_analyze_variable. */
static unsigned int
static_execute (void)
{
struct cgraph_node *node;
struct cgraph_node *w;
struct cgraph_node **order =
XCNEWVEC (struct cgraph_node *, cgraph_n_nodes);
int order_pos = order_pos = ipa_utils_reduced_inorder (order, true, false);
int i;
struct ipa_dfs_info * w_info;
if (!memory_identifier_string)
memory_identifier_string = build_string(7, "memory");
/* There are some shared nodes, in particular the initializers on
static declarations. We do not need to scan them more than once
since all we would be interested in are the addressof
operations. */
visited_nodes = pointer_set_create ();
/* Process all of the functions.
We do not want to process any of the clones so we check that this
is a master clone. However, we do NOT process any
AVAIL_OVERWRITABLE functions (these are never clones) we cannot
guarantee that what we learn about the one we see will be true
for the one that overriders it.
*/
for (node = cgraph_nodes; node; node = node->next)
if (node->analyzed && cgraph_is_master_clone (node))
analyze_function (node);
pointer_set_destroy (visited_nodes);
visited_nodes = NULL;
if (dump_file)
{
dump_cgraph (dump_file);
ipa_utils_print_order(dump_file, "reduced", order, order_pos);
}
/* Propagate the local information thru the call graph to produce
the global information. All the nodes within a cycle will have
the same info so we collapse cycles first. Then we can do the
propagation in one pass from the leaves to the roots. */
for (i = 0; i < order_pos; i++ )
{
enum pure_const_state_e pure_const_state = IPA_CONST;
int count = 0;
node = order[i];
/* Find the worst state for any node in the cycle. */
w = node;
while (w)
{
funct_state w_l = get_function_state (w);
if (pure_const_state < w_l->pure_const_state)
pure_const_state = w_l->pure_const_state;
if (pure_const_state == IPA_NEITHER)
break;
if (!w_l->state_set_in_source)
{
struct cgraph_edge *e;
count++;
/* FIXME!!! Because of pr33826, we cannot have either
immediate or transitive recursive functions marked as
pure or const because dce can delete a function that
is in reality an infinite loop. A better solution
than just outlawing them is to add another bit the
functions to distinguish recursive from non recursive
pure and const function. This would allow the
recursive ones to be cse'd but not dce'd. In this
same vein, we could allow functions with loops to
also be cse'd but not dce'd.
Unfortunately we are late in stage 3, and the fix
described above is is not appropriate. */
if (count > 1)
{
pure_const_state = IPA_NEITHER;
break;
}
for (e = w->callees; e; e = e->next_callee)
{
struct cgraph_node *y = e->callee;
/* Only look at the master nodes and skip external nodes. */
y = cgraph_master_clone (y);
/* Check for immediate recursive functions. See the
FIXME above. */
if (w == y)
{
pure_const_state = IPA_NEITHER;
break;
}
if (y)
{
funct_state y_l = get_function_state (y);
if (pure_const_state < y_l->pure_const_state)
pure_const_state = y_l->pure_const_state;
if (pure_const_state == IPA_NEITHER)
break;
}
}
}
w_info = w->aux;
w = w_info->next_cycle;
}
/* Copy back the region's pure_const_state which is shared by
all nodes in the region. */
w = node;
while (w)
{
funct_state w_l = get_function_state (w);
/* All nodes within a cycle share the same info. */
if (!w_l->state_set_in_source)
{
w_l->pure_const_state = pure_const_state;
switch (pure_const_state)
{
case IPA_CONST:
TREE_READONLY (w->decl) = 1;
if (dump_file)
fprintf (dump_file, "Function found to be const: %s\n",
lang_hooks.decl_printable_name(w->decl, 2));
break;
case IPA_PURE:
DECL_IS_PURE (w->decl) = 1;
if (dump_file)
fprintf (dump_file, "Function found to be pure: %s\n",
lang_hooks.decl_printable_name(w->decl, 2));
break;
default:
break;
}
}
w_info = w->aux;
w = w_info->next_cycle;
}
}
/* Cleanup. */
for (node = cgraph_nodes; node; node = node->next)
/* Get rid of the aux information. */
if (node->aux)
{
w_info = node->aux;
if (w_info->aux)
free (w_info->aux);
free (node->aux);
node->aux = NULL;
}
free (order);
return 0;
}
static bool
gate_pure_const (void)
{
return (flag_unit_at_a_time != 0 && flag_ipa_pure_const
/* Don't bother doing anything if the program has errors. */
&& !(errorcount || sorrycount));
}
struct tree_opt_pass pass_ipa_pure_const =
{
"pure-const", /* name */
gate_pure_const, /* gate */
static_execute, /* execute */
NULL, /* sub */
NULL, /* next */
0, /* static_pass_number */
TV_IPA_PURE_CONST, /* tv_id */
0, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
0, /* todo_flags_finish */
0 /* letter */
};