/* Language independent return value optimizations
|
/* Language independent return value optimizations
|
Copyright (C) 2004, 2005, 2007 Free Software Foundation, Inc.
|
Copyright (C) 2004, 2005, 2007 Free Software Foundation, Inc.
|
|
|
This file is part of GCC.
|
This file is part of GCC.
|
|
|
GCC is free software; you can redistribute it and/or modify
|
GCC is free software; you can redistribute it and/or modify
|
it under the terms of the GNU General Public License as published by
|
it under the terms of the GNU General Public License as published by
|
the Free Software Foundation; either version 3, or (at your option)
|
the Free Software Foundation; either version 3, or (at your option)
|
any later version.
|
any later version.
|
|
|
GCC is distributed in the hope that it will be useful,
|
GCC is distributed in the hope that it will be useful,
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
GNU General Public License for more details.
|
GNU General Public License for more details.
|
|
|
You should have received a copy of the GNU General Public License
|
You should have received a copy of the GNU General Public License
|
along with GCC; see the file COPYING3. If not see
|
along with GCC; see the file COPYING3. If not see
|
<http://www.gnu.org/licenses/>. */
|
<http://www.gnu.org/licenses/>. */
|
|
|
#include "config.h"
|
#include "config.h"
|
#include "system.h"
|
#include "system.h"
|
#include "coretypes.h"
|
#include "coretypes.h"
|
#include "tm.h"
|
#include "tm.h"
|
#include "tree.h"
|
#include "tree.h"
|
#include "rtl.h"
|
#include "rtl.h"
|
#include "function.h"
|
#include "function.h"
|
#include "basic-block.h"
|
#include "basic-block.h"
|
#include "expr.h"
|
#include "expr.h"
|
#include "diagnostic.h"
|
#include "diagnostic.h"
|
#include "tree-flow.h"
|
#include "tree-flow.h"
|
#include "timevar.h"
|
#include "timevar.h"
|
#include "tree-dump.h"
|
#include "tree-dump.h"
|
#include "tree-pass.h"
|
#include "tree-pass.h"
|
#include "langhooks.h"
|
#include "langhooks.h"
|
|
|
/* This file implements return value optimizations for functions which
|
/* This file implements return value optimizations for functions which
|
return aggregate types.
|
return aggregate types.
|
|
|
Basically this pass searches the function for return statements which
|
Basically this pass searches the function for return statements which
|
return a local aggregate. When converted to RTL such statements will
|
return a local aggregate. When converted to RTL such statements will
|
generate a copy from the local aggregate to final return value destination
|
generate a copy from the local aggregate to final return value destination
|
mandated by the target's ABI.
|
mandated by the target's ABI.
|
|
|
That copy can often be avoided by directly constructing the return value
|
That copy can often be avoided by directly constructing the return value
|
into the final destination mandated by the target's ABI.
|
into the final destination mandated by the target's ABI.
|
|
|
This is basically a generic equivalent to the C++ front-end's
|
This is basically a generic equivalent to the C++ front-end's
|
Named Return Value optimization. */
|
Named Return Value optimization. */
|
|
|
struct nrv_data
|
struct nrv_data
|
{
|
{
|
/* This is the temporary (a VAR_DECL) which appears in all of
|
/* This is the temporary (a VAR_DECL) which appears in all of
|
this function's RETURN_EXPR statements. */
|
this function's RETURN_EXPR statements. */
|
tree var;
|
tree var;
|
|
|
/* This is the function's RESULT_DECL. We will replace all occurrences
|
/* This is the function's RESULT_DECL. We will replace all occurrences
|
of VAR with RESULT_DECL when we apply this optimization. */
|
of VAR with RESULT_DECL when we apply this optimization. */
|
tree result;
|
tree result;
|
};
|
};
|
|
|
static tree finalize_nrv_r (tree *, int *, void *);
|
static tree finalize_nrv_r (tree *, int *, void *);
|
|
|
/* Callback for the tree walker.
|
/* Callback for the tree walker.
|
|
|
If TP refers to a RETURN_EXPR, then set the expression being returned
|
If TP refers to a RETURN_EXPR, then set the expression being returned
|
to nrv_data->result.
|
to nrv_data->result.
|
|
|
If TP refers to nrv_data->var, then replace nrv_data->var with
|
If TP refers to nrv_data->var, then replace nrv_data->var with
|
nrv_data->result.
|
nrv_data->result.
|
|
|
If we reach a node where we know all the subtrees are uninteresting,
|
If we reach a node where we know all the subtrees are uninteresting,
|
then set *WALK_SUBTREES to zero. */
|
then set *WALK_SUBTREES to zero. */
|
|
|
static tree
|
static tree
|
finalize_nrv_r (tree *tp, int *walk_subtrees, void *data)
|
finalize_nrv_r (tree *tp, int *walk_subtrees, void *data)
|
{
|
{
|
struct nrv_data *dp = (struct nrv_data *)data;
|
struct nrv_data *dp = (struct nrv_data *)data;
|
|
|
/* No need to walk into types. */
|
/* No need to walk into types. */
|
if (TYPE_P (*tp))
|
if (TYPE_P (*tp))
|
*walk_subtrees = 0;
|
*walk_subtrees = 0;
|
|
|
/* Otherwise replace all occurrences of VAR with RESULT. */
|
/* Otherwise replace all occurrences of VAR with RESULT. */
|
else if (*tp == dp->var)
|
else if (*tp == dp->var)
|
*tp = dp->result;
|
*tp = dp->result;
|
|
|
/* Keep iterating. */
|
/* Keep iterating. */
|
return NULL_TREE;
|
return NULL_TREE;
|
}
|
}
|
|
|
/* Main entry point for return value optimizations.
|
/* Main entry point for return value optimizations.
|
|
|
If this function always returns the same local variable, and that
|
If this function always returns the same local variable, and that
|
local variable is an aggregate type, then replace the variable with
|
local variable is an aggregate type, then replace the variable with
|
the function's DECL_RESULT.
|
the function's DECL_RESULT.
|
|
|
This is the equivalent of the C++ named return value optimization
|
This is the equivalent of the C++ named return value optimization
|
applied to optimized trees in a language independent form. If we
|
applied to optimized trees in a language independent form. If we
|
ever encounter languages which prevent this kind of optimization,
|
ever encounter languages which prevent this kind of optimization,
|
then we could either have the languages register the optimization or
|
then we could either have the languages register the optimization or
|
we could change the gating function to check the current language. */
|
we could change the gating function to check the current language. */
|
|
|
static unsigned int
|
static unsigned int
|
tree_nrv (void)
|
tree_nrv (void)
|
{
|
{
|
tree result = DECL_RESULT (current_function_decl);
|
tree result = DECL_RESULT (current_function_decl);
|
tree result_type = TREE_TYPE (result);
|
tree result_type = TREE_TYPE (result);
|
tree found = NULL;
|
tree found = NULL;
|
basic_block bb;
|
basic_block bb;
|
block_stmt_iterator bsi;
|
block_stmt_iterator bsi;
|
struct nrv_data data;
|
struct nrv_data data;
|
|
|
/* If this function does not return an aggregate type in memory, then
|
/* If this function does not return an aggregate type in memory, then
|
there is nothing to do. */
|
there is nothing to do. */
|
if (!aggregate_value_p (result, current_function_decl))
|
if (!aggregate_value_p (result, current_function_decl))
|
return 0;
|
return 0;
|
|
|
/* Look through each block for assignments to the RESULT_DECL. */
|
/* Look through each block for assignments to the RESULT_DECL. */
|
FOR_EACH_BB (bb)
|
FOR_EACH_BB (bb)
|
{
|
{
|
for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
|
for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
|
{
|
{
|
tree stmt = bsi_stmt (bsi);
|
tree stmt = bsi_stmt (bsi);
|
tree ret_expr;
|
tree ret_expr;
|
|
|
if (TREE_CODE (stmt) == RETURN_EXPR)
|
if (TREE_CODE (stmt) == RETURN_EXPR)
|
{
|
{
|
/* In a function with an aggregate return value, the
|
/* In a function with an aggregate return value, the
|
gimplifier has changed all non-empty RETURN_EXPRs to
|
gimplifier has changed all non-empty RETURN_EXPRs to
|
return the RESULT_DECL. */
|
return the RESULT_DECL. */
|
ret_expr = TREE_OPERAND (stmt, 0);
|
ret_expr = TREE_OPERAND (stmt, 0);
|
if (ret_expr)
|
if (ret_expr)
|
gcc_assert (ret_expr == result);
|
gcc_assert (ret_expr == result);
|
}
|
}
|
else if (TREE_CODE (stmt) == MODIFY_EXPR
|
else if (TREE_CODE (stmt) == MODIFY_EXPR
|
&& TREE_OPERAND (stmt, 0) == result)
|
&& TREE_OPERAND (stmt, 0) == result)
|
{
|
{
|
ret_expr = TREE_OPERAND (stmt, 1);
|
ret_expr = TREE_OPERAND (stmt, 1);
|
|
|
/* Now verify that this return statement uses the same value
|
/* Now verify that this return statement uses the same value
|
as any previously encountered return statement. */
|
as any previously encountered return statement. */
|
if (found != NULL)
|
if (found != NULL)
|
{
|
{
|
/* If we found a return statement using a different variable
|
/* If we found a return statement using a different variable
|
than previous return statements, then we can not perform
|
than previous return statements, then we can not perform
|
NRV optimizations. */
|
NRV optimizations. */
|
if (found != ret_expr)
|
if (found != ret_expr)
|
return 0;
|
return 0;
|
}
|
}
|
else
|
else
|
found = ret_expr;
|
found = ret_expr;
|
|
|
/* The returned value must be a local automatic variable of the
|
/* The returned value must be a local automatic variable of the
|
same type and alignment as the function's result. */
|
same type and alignment as the function's result. */
|
if (TREE_CODE (found) != VAR_DECL
|
if (TREE_CODE (found) != VAR_DECL
|
|| TREE_THIS_VOLATILE (found)
|
|| TREE_THIS_VOLATILE (found)
|
|| DECL_CONTEXT (found) != current_function_decl
|
|| DECL_CONTEXT (found) != current_function_decl
|
|| TREE_STATIC (found)
|
|| TREE_STATIC (found)
|
|| TREE_ADDRESSABLE (found)
|
|| TREE_ADDRESSABLE (found)
|
|| DECL_ALIGN (found) > DECL_ALIGN (result)
|
|| DECL_ALIGN (found) > DECL_ALIGN (result)
|
|| !lang_hooks.types_compatible_p (TREE_TYPE (found),
|
|| !lang_hooks.types_compatible_p (TREE_TYPE (found),
|
result_type))
|
result_type))
|
return 0;
|
return 0;
|
}
|
}
|
else if (TREE_CODE (stmt) == MODIFY_EXPR)
|
else if (TREE_CODE (stmt) == MODIFY_EXPR)
|
{
|
{
|
tree addr = get_base_address (TREE_OPERAND (stmt, 0));
|
tree addr = get_base_address (TREE_OPERAND (stmt, 0));
|
/* If there's any MODIFY of component of RESULT,
|
/* If there's any MODIFY of component of RESULT,
|
then bail out. */
|
then bail out. */
|
if (addr && addr == result)
|
if (addr && addr == result)
|
return 0;
|
return 0;
|
}
|
}
|
}
|
}
|
}
|
}
|
|
|
if (!found)
|
if (!found)
|
return 0;
|
return 0;
|
|
|
/* If dumping details, then note once and only the NRV replacement. */
|
/* If dumping details, then note once and only the NRV replacement. */
|
if (dump_file && (dump_flags & TDF_DETAILS))
|
if (dump_file && (dump_flags & TDF_DETAILS))
|
{
|
{
|
fprintf (dump_file, "NRV Replaced: ");
|
fprintf (dump_file, "NRV Replaced: ");
|
print_generic_expr (dump_file, found, dump_flags);
|
print_generic_expr (dump_file, found, dump_flags);
|
fprintf (dump_file, " with: ");
|
fprintf (dump_file, " with: ");
|
print_generic_expr (dump_file, result, dump_flags);
|
print_generic_expr (dump_file, result, dump_flags);
|
fprintf (dump_file, "\n");
|
fprintf (dump_file, "\n");
|
}
|
}
|
|
|
/* At this point we know that all the return statements return the
|
/* At this point we know that all the return statements return the
|
same local which has suitable attributes for NRV. Copy debugging
|
same local which has suitable attributes for NRV. Copy debugging
|
information from FOUND to RESULT. */
|
information from FOUND to RESULT. */
|
DECL_NAME (result) = DECL_NAME (found);
|
DECL_NAME (result) = DECL_NAME (found);
|
DECL_SOURCE_LOCATION (result) = DECL_SOURCE_LOCATION (found);
|
DECL_SOURCE_LOCATION (result) = DECL_SOURCE_LOCATION (found);
|
DECL_ABSTRACT_ORIGIN (result) = DECL_ABSTRACT_ORIGIN (found);
|
DECL_ABSTRACT_ORIGIN (result) = DECL_ABSTRACT_ORIGIN (found);
|
TREE_ADDRESSABLE (result) = TREE_ADDRESSABLE (found);
|
TREE_ADDRESSABLE (result) = TREE_ADDRESSABLE (found);
|
|
|
/* Now walk through the function changing all references to VAR to be
|
/* Now walk through the function changing all references to VAR to be
|
RESULT. */
|
RESULT. */
|
data.var = found;
|
data.var = found;
|
data.result = result;
|
data.result = result;
|
FOR_EACH_BB (bb)
|
FOR_EACH_BB (bb)
|
{
|
{
|
for (bsi = bsi_start (bb); !bsi_end_p (bsi); )
|
for (bsi = bsi_start (bb); !bsi_end_p (bsi); )
|
{
|
{
|
tree *tp = bsi_stmt_ptr (bsi);
|
tree *tp = bsi_stmt_ptr (bsi);
|
/* If this is a copy from VAR to RESULT, remove it. */
|
/* If this is a copy from VAR to RESULT, remove it. */
|
if (TREE_CODE (*tp) == MODIFY_EXPR
|
if (TREE_CODE (*tp) == MODIFY_EXPR
|
&& TREE_OPERAND (*tp, 0) == result
|
&& TREE_OPERAND (*tp, 0) == result
|
&& TREE_OPERAND (*tp, 1) == found)
|
&& TREE_OPERAND (*tp, 1) == found)
|
bsi_remove (&bsi, true);
|
bsi_remove (&bsi, true);
|
else
|
else
|
{
|
{
|
walk_tree (tp, finalize_nrv_r, &data, 0);
|
walk_tree (tp, finalize_nrv_r, &data, 0);
|
bsi_next (&bsi);
|
bsi_next (&bsi);
|
}
|
}
|
}
|
}
|
}
|
}
|
|
|
/* FOUND is no longer used. Ensure it gets removed. */
|
/* FOUND is no longer used. Ensure it gets removed. */
|
var_ann (found)->used = 0;
|
var_ann (found)->used = 0;
|
return 0;
|
return 0;
|
}
|
}
|
|
|
struct tree_opt_pass pass_nrv =
|
struct tree_opt_pass pass_nrv =
|
{
|
{
|
"nrv", /* name */
|
"nrv", /* name */
|
NULL, /* gate */
|
NULL, /* gate */
|
tree_nrv, /* execute */
|
tree_nrv, /* execute */
|
NULL, /* sub */
|
NULL, /* sub */
|
NULL, /* next */
|
NULL, /* next */
|
0, /* static_pass_number */
|
0, /* static_pass_number */
|
TV_TREE_NRV, /* tv_id */
|
TV_TREE_NRV, /* tv_id */
|
PROP_cfg, /* properties_required */
|
PROP_cfg, /* properties_required */
|
0, /* properties_provided */
|
0, /* properties_provided */
|
0, /* properties_destroyed */
|
0, /* properties_destroyed */
|
0, /* todo_flags_start */
|
0, /* todo_flags_start */
|
TODO_dump_func | TODO_ggc_collect, /* todo_flags_finish */
|
TODO_dump_func | TODO_ggc_collect, /* todo_flags_finish */
|
0 /* letter */
|
0 /* letter */
|
};
|
};
|
|
|
/* Determine (pessimistically) whether DEST is available for NRV
|
/* Determine (pessimistically) whether DEST is available for NRV
|
optimization, where DEST is expected to be the LHS of a modify
|
optimization, where DEST is expected to be the LHS of a modify
|
expression where the RHS is a function returning an aggregate.
|
expression where the RHS is a function returning an aggregate.
|
|
|
We search for a base VAR_DECL and look to see if it, or any of its
|
We search for a base VAR_DECL and look to see if it, or any of its
|
subvars are clobbered. Note that we could do better, for example, by
|
subvars are clobbered. Note that we could do better, for example, by
|
attempting to doing points-to analysis on INDIRECT_REFs. */
|
attempting to doing points-to analysis on INDIRECT_REFs. */
|
|
|
static bool
|
static bool
|
dest_safe_for_nrv_p (tree dest)
|
dest_safe_for_nrv_p (tree dest)
|
{
|
{
|
switch (TREE_CODE (dest))
|
switch (TREE_CODE (dest))
|
{
|
{
|
case VAR_DECL:
|
case VAR_DECL:
|
{
|
{
|
subvar_t subvar;
|
subvar_t subvar;
|
if (is_call_clobbered (dest))
|
if (is_call_clobbered (dest))
|
return false;
|
return false;
|
for (subvar = get_subvars_for_var (dest);
|
for (subvar = get_subvars_for_var (dest);
|
subvar;
|
subvar;
|
subvar = subvar->next)
|
subvar = subvar->next)
|
if (is_call_clobbered (subvar->var))
|
if (is_call_clobbered (subvar->var))
|
return false;
|
return false;
|
return true;
|
return true;
|
}
|
}
|
case ARRAY_REF:
|
case ARRAY_REF:
|
case COMPONENT_REF:
|
case COMPONENT_REF:
|
return dest_safe_for_nrv_p (TREE_OPERAND (dest, 0));
|
return dest_safe_for_nrv_p (TREE_OPERAND (dest, 0));
|
default:
|
default:
|
return false;
|
return false;
|
}
|
}
|
}
|
}
|
|
|
/* Walk through the function looking for MODIFY_EXPRs with calls that
|
/* Walk through the function looking for MODIFY_EXPRs with calls that
|
return in memory on the RHS. For each of these, determine whether it is
|
return in memory on the RHS. For each of these, determine whether it is
|
safe to pass the address of the LHS as the return slot, and mark the
|
safe to pass the address of the LHS as the return slot, and mark the
|
call appropriately if so.
|
call appropriately if so.
|
|
|
The NRV shares the return slot with a local variable in the callee; this
|
The NRV shares the return slot with a local variable in the callee; this
|
optimization shares the return slot with the target of the call within
|
optimization shares the return slot with the target of the call within
|
the caller. If the NRV is performed (which we can't know in general),
|
the caller. If the NRV is performed (which we can't know in general),
|
this optimization is safe if the address of the target has not
|
this optimization is safe if the address of the target has not
|
escaped prior to the call. If it has, modifications to the local
|
escaped prior to the call. If it has, modifications to the local
|
variable will produce visible changes elsewhere, as in PR c++/19317. */
|
variable will produce visible changes elsewhere, as in PR c++/19317. */
|
|
|
static unsigned int
|
static unsigned int
|
execute_return_slot_opt (void)
|
execute_return_slot_opt (void)
|
{
|
{
|
basic_block bb;
|
basic_block bb;
|
|
|
FOR_EACH_BB (bb)
|
FOR_EACH_BB (bb)
|
{
|
{
|
block_stmt_iterator i;
|
block_stmt_iterator i;
|
for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
|
for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
|
{
|
{
|
tree stmt = bsi_stmt (i);
|
tree stmt = bsi_stmt (i);
|
tree call;
|
tree call;
|
|
|
if (TREE_CODE (stmt) == MODIFY_EXPR
|
if (TREE_CODE (stmt) == MODIFY_EXPR
|
&& (call = TREE_OPERAND (stmt, 1),
|
&& (call = TREE_OPERAND (stmt, 1),
|
TREE_CODE (call) == CALL_EXPR)
|
TREE_CODE (call) == CALL_EXPR)
|
&& !CALL_EXPR_RETURN_SLOT_OPT (call)
|
&& !CALL_EXPR_RETURN_SLOT_OPT (call)
|
&& aggregate_value_p (call, call))
|
&& aggregate_value_p (call, call))
|
/* Check if the location being assigned to is
|
/* Check if the location being assigned to is
|
call-clobbered. */
|
call-clobbered. */
|
CALL_EXPR_RETURN_SLOT_OPT (call) =
|
CALL_EXPR_RETURN_SLOT_OPT (call) =
|
dest_safe_for_nrv_p (TREE_OPERAND (stmt, 0)) ? 1 : 0;
|
dest_safe_for_nrv_p (TREE_OPERAND (stmt, 0)) ? 1 : 0;
|
}
|
}
|
}
|
}
|
return 0;
|
return 0;
|
}
|
}
|
|
|
struct tree_opt_pass pass_return_slot =
|
struct tree_opt_pass pass_return_slot =
|
{
|
{
|
"retslot", /* name */
|
"retslot", /* name */
|
NULL, /* gate */
|
NULL, /* gate */
|
execute_return_slot_opt, /* execute */
|
execute_return_slot_opt, /* execute */
|
NULL, /* sub */
|
NULL, /* sub */
|
NULL, /* next */
|
NULL, /* next */
|
0, /* static_pass_number */
|
0, /* static_pass_number */
|
0, /* tv_id */
|
0, /* tv_id */
|
PROP_ssa | PROP_alias, /* properties_required */
|
PROP_ssa | PROP_alias, /* properties_required */
|
0, /* properties_provided */
|
0, /* properties_provided */
|
0, /* properties_destroyed */
|
0, /* properties_destroyed */
|
0, /* todo_flags_start */
|
0, /* todo_flags_start */
|
0, /* todo_flags_finish */
|
0, /* todo_flags_finish */
|
0 /* letter */
|
0 /* letter */
|
};
|
};
|
|
|
