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/* Tree lowering pass. Lowers GIMPLE into unstructured form.
Copyright (C) 2003 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, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "rtl.h"
#include "errors.h"
#include "varray.h"
#include "tree-gimple.h"
#include "tree-inline.h"
#include "diagnostic.h"
#include "langhooks.h"
#include "langhooks-def.h"
#include "tree-flow.h"
#include "timevar.h"
#include "except.h"
#include "hashtab.h"
#include "flags.h"
#include "function.h"
#include "expr.h"
#include "toplev.h"
#include "tree-pass.h"
struct lower_data
{
/* Block the current statement belongs to. */
tree block;
/* A TREE_LIST of label and return statements to be moved to the end
of the function. */
tree return_statements;
};
static void lower_stmt (tree_stmt_iterator *, struct lower_data *);
static void lower_bind_expr (tree_stmt_iterator *, struct lower_data *);
static void lower_cond_expr (tree_stmt_iterator *, struct lower_data *);
static void lower_return_expr (tree_stmt_iterator *, struct lower_data *);
static bool expand_var_p (tree);
/* Lowers the body of current_function_decl. */
static void
lower_function_body (void)
{
struct lower_data data;
tree *body_p = &DECL_SAVED_TREE (current_function_decl);
tree bind = *body_p;
tree_stmt_iterator i;
tree t, x;
if (TREE_CODE (bind) != BIND_EXPR)
abort ();
data.block = DECL_INITIAL (current_function_decl);
BLOCK_SUBBLOCKS (data.block) = NULL_TREE;
BLOCK_CHAIN (data.block) = NULL_TREE;
TREE_ASM_WRITTEN (data.block) = 1;
data.return_statements = NULL_TREE;
*body_p = alloc_stmt_list ();
i = tsi_start (*body_p);
tsi_link_after (&i, bind, TSI_NEW_STMT);
lower_bind_expr (&i, &data);
i = tsi_last (*body_p);
/* If the function falls off the end, we need a null return statement.
If we've already got one in the return_statements list, we don't
need to do anything special. Otherwise build one by hand. */
if (block_may_fallthru (*body_p)
&& (data.return_statements == NULL
|| TREE_OPERAND (TREE_VALUE (data.return_statements), 0) != NULL))
{
x = build (RETURN_EXPR, void_type_node, NULL);
SET_EXPR_LOCATION (x, cfun->function_end_locus);
tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
}
/* If we lowered any return statements, emit the representative
at the end of the function. */
for (t = data.return_statements ; t ; t = TREE_CHAIN (t))
{
x = build (LABEL_EXPR, void_type_node, TREE_PURPOSE (t));
tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
/* Remove the line number from the representative return statement.
It now fills in for many such returns. Failure to remove this
will result in incorrect results for coverage analysis. */
x = TREE_VALUE (t);
#ifdef USE_MAPPED_LOCATION
SET_EXPR_LOCATION (x, UNKNOWN_LOCATION);
#else
SET_EXPR_LOCUS (x, NULL);
#endif
tsi_link_after (&i, x, TSI_CONTINUE_LINKING);
}
if (data.block != DECL_INITIAL (current_function_decl))
abort ();
BLOCK_SUBBLOCKS (data.block)
= blocks_nreverse (BLOCK_SUBBLOCKS (data.block));
clear_block_marks (data.block);
/* Avoid producing notes for blocks. */
cfun->dont_emit_block_notes = 1;
reset_block_changes ();
}
struct tree_opt_pass pass_lower_cf =
{
"lower", /* name */
NULL, /* gate */
lower_function_body, /* execute */
NULL, /* sub */
NULL, /* next */
0, /* static_pass_number */
0, /* tv_id */
PROP_gimple_any, /* properties_required */
PROP_gimple_lcf, /* properties_provided */
PROP_gimple_any, /* properties_destroyed */
0, /* todo_flags_start */
TODO_dump_func /* todo_flags_finish */
};
/* Lowers the EXPR. Unlike gimplification the statements are not relowered
when they are changed -- if this has to be done, the lowering routine must
do it explicitly. DATA is passed through the recursion. */
void
lower_stmt_body (tree expr, struct lower_data *data)
{
tree_stmt_iterator tsi;
for (tsi = tsi_start (expr); !tsi_end_p (tsi); )
lower_stmt (&tsi, data);
}
/* Lowers statement TSI. DATA is passed through the recursion. */
static void
lower_stmt (tree_stmt_iterator *tsi, struct lower_data *data)
{
tree stmt = tsi_stmt (*tsi);
if (EXPR_HAS_LOCATION (stmt) && data)
TREE_BLOCK (stmt) = data->block;
switch (TREE_CODE (stmt))
{
case BIND_EXPR:
lower_bind_expr (tsi, data);
return;
case COND_EXPR:
lower_cond_expr (tsi, data);
return;
case RETURN_EXPR:
lower_return_expr (tsi, data);
return;
case TRY_FINALLY_EXPR:
case TRY_CATCH_EXPR:
lower_stmt_body (TREE_OPERAND (stmt, 0), data);
lower_stmt_body (TREE_OPERAND (stmt, 1), data);
break;
case CATCH_EXPR:
lower_stmt_body (CATCH_BODY (stmt), data);
break;
case EH_FILTER_EXPR:
lower_stmt_body (EH_FILTER_FAILURE (stmt), data);
break;
case NOP_EXPR:
case ASM_EXPR:
case MODIFY_EXPR:
case CALL_EXPR:
case GOTO_EXPR:
case LABEL_EXPR:
case VA_ARG_EXPR:
case SWITCH_EXPR:
break;
default:
print_node_brief (stderr, "", stmt, 0);
case COMPOUND_EXPR:
abort ();
}
tsi_next (tsi);
}
/* Lowers a bind_expr TSI. DATA is passed through the recursion. */
static void
lower_bind_expr (tree_stmt_iterator *tsi, struct lower_data *data)
{
tree old_block = data->block;
tree stmt = tsi_stmt (*tsi);
tree new_block = BIND_EXPR_BLOCK (stmt);
if (new_block)
{
if (new_block == old_block)
{
/* The outermost block of the original function may not be the
outermost statement chain of the gimplified function. So we
may see the outermost block just inside the function. */
if (new_block != DECL_INITIAL (current_function_decl))
abort ();
new_block = NULL;
}
else
{
/* We do not expect to handle duplicate blocks. */
if (TREE_ASM_WRITTEN (new_block))
abort ();
TREE_ASM_WRITTEN (new_block) = 1;
/* Block tree may get clobbered by inlining. Normally this would
be fixed in rest_of_decl_compilation using block notes, but
since we are not going to emit them, it is up to us. */
BLOCK_CHAIN (new_block) = BLOCK_SUBBLOCKS (old_block);
BLOCK_SUBBLOCKS (old_block) = new_block;
BLOCK_SUBBLOCKS (new_block) = NULL_TREE;
BLOCK_SUPERCONTEXT (new_block) = old_block;
data->block = new_block;
}
}
record_vars (BIND_EXPR_VARS (stmt));
lower_stmt_body (BIND_EXPR_BODY (stmt), data);
if (new_block)
{
if (data->block != new_block)
abort ();
BLOCK_SUBBLOCKS (new_block)
= blocks_nreverse (BLOCK_SUBBLOCKS (new_block));
data->block = old_block;
}
/* The BIND_EXPR no longer carries any useful information -- kill it. */
tsi_link_before (tsi, BIND_EXPR_BODY (stmt), TSI_SAME_STMT);
tsi_delink (tsi);
}
/* Try to determine if we can fall out of the bottom of BLOCK. This guess
need not be 100% accurate; simply be conservative and return true if we
don't know. This is used only to avoid stupidly generating extra code.
If we're wrong, we'll just delete the extra code later. */
bool
block_may_fallthru (tree block)
{
tree stmt = expr_last (block);
switch (stmt ? TREE_CODE (stmt) : ERROR_MARK)
{
case GOTO_EXPR:
case RETURN_EXPR:
case RESX_EXPR:
case SWITCH_EXPR:
/* Easy cases. If the last statement of the block implies
control transfer, then we can't fall through. */
return false;
case COND_EXPR:
if (block_may_fallthru (COND_EXPR_THEN (stmt)))
return true;
return block_may_fallthru (COND_EXPR_ELSE (stmt));
case BIND_EXPR:
return block_may_fallthru (BIND_EXPR_BODY (stmt));
case TRY_FINALLY_EXPR:
return block_may_fallthru (TREE_OPERAND (stmt, 1));
case MODIFY_EXPR:
if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)
stmt = TREE_OPERAND (stmt, 1);
else
return true;
/* FALLTHRU */
case CALL_EXPR:
/* Functions that do not return do not fall through. */
return (call_expr_flags (stmt) & ECF_NORETURN) == 0;
default:
return true;
}
}
/* Lowers a cond_expr TSI. DATA is passed through the recursion. */
static void
lower_cond_expr (tree_stmt_iterator *tsi, struct lower_data *data)
{
tree stmt = tsi_stmt (*tsi);
bool then_is_goto, else_is_goto;
tree then_branch, else_branch;
tree then_goto, else_goto;
then_branch = COND_EXPR_THEN (stmt);
else_branch = COND_EXPR_ELSE (stmt);
lower_stmt_body (then_branch, data);
lower_stmt_body (else_branch, data);
then_goto = expr_only (then_branch);
then_is_goto = then_goto && simple_goto_p (then_goto);
else_goto = expr_only (else_branch);
else_is_goto = else_goto && simple_goto_p (else_goto);
if (!then_is_goto || !else_is_goto)
{
tree then_label, else_label, end_label, t;
then_label = NULL_TREE;
else_label = NULL_TREE;
end_label = NULL_TREE;
/* Replace the cond_expr with explicit gotos. */
if (!then_is_goto)
{
t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
if (TREE_SIDE_EFFECTS (then_branch))
then_label = t;
else
end_label = t;
then_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
}
if (!else_is_goto)
{
t = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
if (TREE_SIDE_EFFECTS (else_branch))
else_label = t;
else
{
/* Both THEN and ELSE can be no-ops if one or both contained an
empty BIND_EXPR that was associated with the toplevel block
of an inlined function. In that case remove_useless_stmts
can't have cleaned things up for us; kill the whole
conditional now. */
if (end_label)
{
tsi_delink (tsi);
return;
}
else
end_label = t;
}
else_goto = build_and_jump (&LABEL_EXPR_LABEL (t));
}
if (then_label)
{
bool may_fallthru = block_may_fallthru (then_branch);
tsi_link_after (tsi, then_label, TSI_CONTINUE_LINKING);
tsi_link_after (tsi, then_branch, TSI_CONTINUE_LINKING);
if (else_label && may_fallthru)
{
end_label = build1 (LABEL_EXPR, void_type_node, NULL_TREE);
t = build_and_jump (&LABEL_EXPR_LABEL (end_label));
tsi_link_after (tsi, t, TSI_CONTINUE_LINKING);
}
}
if (else_label)
{
tsi_link_after (tsi, else_label, TSI_CONTINUE_LINKING);
tsi_link_after (tsi, else_branch, TSI_CONTINUE_LINKING);
}
if (end_label)
tsi_link_after (tsi, end_label, TSI_CONTINUE_LINKING);
}
COND_EXPR_THEN (stmt) = then_goto;
COND_EXPR_ELSE (stmt) = else_goto;
tsi_next (tsi);
}
static void
lower_return_expr (tree_stmt_iterator *tsi, struct lower_data *data)
{
tree stmt = tsi_stmt (*tsi);
tree value, t, label;
/* Extract the value being returned. */
value = TREE_OPERAND (stmt, 0);
if (value && TREE_CODE (value) == MODIFY_EXPR)
value = TREE_OPERAND (value, 1);
/* Match this up with an existing return statement that's been created. */
for (t = data->return_statements; t ; t = TREE_CHAIN (t))
{
tree tvalue = TREE_OPERAND (TREE_VALUE (t), 0);
if (tvalue && TREE_CODE (tvalue) == MODIFY_EXPR)
tvalue = TREE_OPERAND (tvalue, 1);
if (value == tvalue)
{
label = TREE_PURPOSE (t);
goto found;
}
}
/* Not found. Create a new label and record the return statement. */
label = create_artificial_label ();
data->return_statements = tree_cons (label, stmt, data->return_statements);
/* Generate a goto statement and remove the return statement. */
found:
t = build (GOTO_EXPR, void_type_node, label);
SET_EXPR_LOCUS (t, EXPR_LOCUS (stmt));
tsi_link_before (tsi, t, TSI_SAME_STMT);
tsi_delink (tsi);
}
/* Record the variables in VARS. */
void
record_vars (tree vars)
{
for (; vars; vars = TREE_CHAIN (vars))
{
tree var = vars;
/* Nothing to do in this case. */
if (DECL_EXTERNAL (var))
continue;
if (TREE_CODE (var) == FUNCTION_DECL)
continue;
/* Record the variable. */
cfun->unexpanded_var_list = tree_cons (NULL_TREE, var,
cfun->unexpanded_var_list);
}
}
/* Check whether to expand a variable VAR. */
static bool
expand_var_p (tree var)
{
struct var_ann_d *ann;
if (TREE_CODE (var) != VAR_DECL)
return true;
/* Remove all unused, unaliased temporaries. Also remove unused, unaliased
local variables during highly optimizing compilations. */
ann = var_ann (var);
if (ann
&& ! ann->may_aliases
&& ! ann->used
&& ! ann->has_hidden_use
&& ! TREE_ADDRESSABLE (var)
&& ! TREE_THIS_VOLATILE (var)
&& (DECL_ARTIFICIAL (var) || optimize >= 2))
return false;
return true;
}
/* Throw away variables that are unused. */
static void
remove_useless_vars (void)
{
tree var, *cell;
for (cell = &cfun->unexpanded_var_list; *cell; )
{
var = TREE_VALUE (*cell);
if (!expand_var_p (var))
{
*cell = TREE_CHAIN (*cell);
continue;
}
cell = &TREE_CHAIN (*cell);
}
}
/* Expand variables in the unexpanded_var_list. */
void
expand_used_vars (void)
{
tree cell;
cfun->unexpanded_var_list = nreverse (cfun->unexpanded_var_list);
for (cell = cfun->unexpanded_var_list; cell; cell = TREE_CHAIN (cell))
expand_var (TREE_VALUE (cell));
cfun->unexpanded_var_list = NULL_TREE;
}
struct tree_opt_pass pass_remove_useless_vars =
{
"vars", /* name */
NULL, /* gate */
remove_useless_vars, /* execute */
NULL, /* sub */
NULL, /* next */
0, /* static_pass_number */
0, /* tv_id */
0, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
TODO_dump_func /* todo_flags_finish */
};
|