forked from illumos/gcc
/
stor-layout.c
2322 lines (1962 loc) · 74.3 KB
/
stor-layout.c
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/* C-compiler utilities for types and variables storage layout
Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1996, 1998,
1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
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 3, 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 COPYING3. If not see
<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "rtl.h"
#include "tm_p.h"
#include "flags.h"
#include "function.h"
#include "expr.h"
#include "output.h"
#include "toplev.h"
#include "ggc.h"
#include "target.h"
#include "langhooks.h"
#include "regs.h"
#include "params.h"
/* Data type for the expressions representing sizes of data types.
It is the first integer type laid out. */
tree sizetype_tab[(int) TYPE_KIND_LAST];
/* If nonzero, this is an upper limit on alignment of structure fields.
The value is measured in bits. */
unsigned int maximum_field_alignment = TARGET_DEFAULT_PACK_STRUCT * BITS_PER_UNIT;
/* ... and its original value in bytes, specified via -fpack-struct=<value>. */
unsigned int initial_max_fld_align = TARGET_DEFAULT_PACK_STRUCT;
/* Nonzero if all REFERENCE_TYPEs are internal and hence should be
allocated in Pmode, not ptr_mode. Set only by internal_reference_types
called only by a front end. */
static int reference_types_internal = 0;
static void finalize_record_size (record_layout_info);
static void finalize_type_size (tree);
static void place_union_field (record_layout_info, tree);
#if defined (PCC_BITFIELD_TYPE_MATTERS) || defined (BITFIELD_NBYTES_LIMITED)
static int excess_unit_span (HOST_WIDE_INT, HOST_WIDE_INT, HOST_WIDE_INT,
HOST_WIDE_INT, tree);
#endif
extern void debug_rli (record_layout_info);
/* SAVE_EXPRs for sizes of types and decls, waiting to be expanded. */
static GTY(()) tree pending_sizes;
/* Show that REFERENCE_TYPES are internal and should be Pmode. Called only
by front end. */
void
internal_reference_types (void)
{
reference_types_internal = 1;
}
/* Get a list of all the objects put on the pending sizes list. */
tree
get_pending_sizes (void)
{
tree chain = pending_sizes;
pending_sizes = 0;
return chain;
}
/* Add EXPR to the pending sizes list. */
void
put_pending_size (tree expr)
{
/* Strip any simple arithmetic from EXPR to see if it has an underlying
SAVE_EXPR. */
expr = skip_simple_arithmetic (expr);
if (TREE_CODE (expr) == SAVE_EXPR)
pending_sizes = tree_cons (NULL_TREE, expr, pending_sizes);
}
/* Put a chain of objects into the pending sizes list, which must be
empty. */
void
put_pending_sizes (tree chain)
{
gcc_assert (!pending_sizes);
pending_sizes = chain;
}
/* Given a size SIZE that may not be a constant, return a SAVE_EXPR
to serve as the actual size-expression for a type or decl. */
tree
variable_size (tree size)
{
tree save;
/* If the language-processor is to take responsibility for variable-sized
items (e.g., languages which have elaboration procedures like Ada),
just return SIZE unchanged. Likewise for self-referential sizes and
constant sizes. */
if (TREE_CONSTANT (size)
|| lang_hooks.decls.global_bindings_p () < 0
|| CONTAINS_PLACEHOLDER_P (size))
return size;
size = save_expr (size);
/* If an array with a variable number of elements is declared, and
the elements require destruction, we will emit a cleanup for the
array. That cleanup is run both on normal exit from the block
and in the exception-handler for the block. Normally, when code
is used in both ordinary code and in an exception handler it is
`unsaved', i.e., all SAVE_EXPRs are recalculated. However, we do
not wish to do that here; the array-size is the same in both
places. */
save = skip_simple_arithmetic (size);
if (cfun && cfun->dont_save_pending_sizes_p)
/* The front-end doesn't want us to keep a list of the expressions
that determine sizes for variable size objects. Trust it. */
return size;
if (lang_hooks.decls.global_bindings_p ())
{
if (TREE_CONSTANT (size))
error ("type size can%'t be explicitly evaluated");
else
error ("variable-size type declared outside of any function");
return size_one_node;
}
put_pending_size (save);
return size;
}
#ifndef MAX_FIXED_MODE_SIZE
#define MAX_FIXED_MODE_SIZE GET_MODE_BITSIZE (DImode)
#endif
/* Return the machine mode to use for a nonscalar of SIZE bits. The
mode must be in class MCLASS, and have exactly that many value bits;
it may have padding as well. If LIMIT is nonzero, modes of wider
than MAX_FIXED_MODE_SIZE will not be used. */
enum machine_mode
mode_for_size (unsigned int size, enum mode_class mclass, int limit)
{
enum machine_mode mode;
if (limit && size > MAX_FIXED_MODE_SIZE)
return BLKmode;
/* Get the first mode which has this size, in the specified class. */
for (mode = GET_CLASS_NARROWEST_MODE (mclass); mode != VOIDmode;
mode = GET_MODE_WIDER_MODE (mode))
if (GET_MODE_PRECISION (mode) == size)
return mode;
return BLKmode;
}
/* Similar, except passed a tree node. */
enum machine_mode
mode_for_size_tree (const_tree size, enum mode_class mclass, int limit)
{
unsigned HOST_WIDE_INT uhwi;
unsigned int ui;
if (!host_integerp (size, 1))
return BLKmode;
uhwi = tree_low_cst (size, 1);
ui = uhwi;
if (uhwi != ui)
return BLKmode;
return mode_for_size (ui, mclass, limit);
}
/* Similar, but never return BLKmode; return the narrowest mode that
contains at least the requested number of value bits. */
enum machine_mode
smallest_mode_for_size (unsigned int size, enum mode_class mclass)
{
enum machine_mode mode;
/* Get the first mode which has at least this size, in the
specified class. */
for (mode = GET_CLASS_NARROWEST_MODE (mclass); mode != VOIDmode;
mode = GET_MODE_WIDER_MODE (mode))
if (GET_MODE_PRECISION (mode) >= size)
return mode;
gcc_unreachable ();
}
/* Find an integer mode of the exact same size, or BLKmode on failure. */
enum machine_mode
int_mode_for_mode (enum machine_mode mode)
{
switch (GET_MODE_CLASS (mode))
{
case MODE_INT:
case MODE_PARTIAL_INT:
break;
case MODE_COMPLEX_INT:
case MODE_COMPLEX_FLOAT:
case MODE_FLOAT:
case MODE_DECIMAL_FLOAT:
case MODE_VECTOR_INT:
case MODE_VECTOR_FLOAT:
case MODE_FRACT:
case MODE_ACCUM:
case MODE_UFRACT:
case MODE_UACCUM:
case MODE_VECTOR_FRACT:
case MODE_VECTOR_ACCUM:
case MODE_VECTOR_UFRACT:
case MODE_VECTOR_UACCUM:
mode = mode_for_size (GET_MODE_BITSIZE (mode), MODE_INT, 0);
break;
case MODE_RANDOM:
if (mode == BLKmode)
break;
/* ... fall through ... */
case MODE_CC:
default:
gcc_unreachable ();
}
return mode;
}
/* Return the alignment of MODE. This will be bounded by 1 and
BIGGEST_ALIGNMENT. */
unsigned int
get_mode_alignment (enum machine_mode mode)
{
return MIN (BIGGEST_ALIGNMENT, MAX (1, mode_base_align[mode]*BITS_PER_UNIT));
}
/* Subroutine of layout_decl: Force alignment required for the data type.
But if the decl itself wants greater alignment, don't override that. */
static inline void
do_type_align (tree type, tree decl)
{
if (TYPE_ALIGN (type) > DECL_ALIGN (decl))
{
DECL_ALIGN (decl) = TYPE_ALIGN (type);
if (TREE_CODE (decl) == FIELD_DECL)
DECL_USER_ALIGN (decl) = TYPE_USER_ALIGN (type);
}
}
/* Set the size, mode and alignment of a ..._DECL node.
TYPE_DECL does need this for C++.
Note that LABEL_DECL and CONST_DECL nodes do not need this,
and FUNCTION_DECL nodes have them set up in a special (and simple) way.
Don't call layout_decl for them.
KNOWN_ALIGN is the amount of alignment we can assume this
decl has with no special effort. It is relevant only for FIELD_DECLs
and depends on the previous fields.
All that matters about KNOWN_ALIGN is which powers of 2 divide it.
If KNOWN_ALIGN is 0, it means, "as much alignment as you like":
the record will be aligned to suit. */
void
layout_decl (tree decl, unsigned int known_align)
{
tree type = TREE_TYPE (decl);
enum tree_code code = TREE_CODE (decl);
rtx rtl = NULL_RTX;
if (code == CONST_DECL)
return;
gcc_assert (code == VAR_DECL || code == PARM_DECL || code == RESULT_DECL
|| code == TYPE_DECL ||code == FIELD_DECL);
rtl = DECL_RTL_IF_SET (decl);
if (type == error_mark_node)
type = void_type_node;
/* Usually the size and mode come from the data type without change,
however, the front-end may set the explicit width of the field, so its
size may not be the same as the size of its type. This happens with
bitfields, of course (an `int' bitfield may be only 2 bits, say), but it
also happens with other fields. For example, the C++ front-end creates
zero-sized fields corresponding to empty base classes, and depends on
layout_type setting DECL_FIELD_BITPOS correctly for the field. Set the
size in bytes from the size in bits. If we have already set the mode,
don't set it again since we can be called twice for FIELD_DECLs. */
DECL_UNSIGNED (decl) = TYPE_UNSIGNED (type);
if (DECL_MODE (decl) == VOIDmode)
DECL_MODE (decl) = TYPE_MODE (type);
if (DECL_SIZE (decl) == 0)
{
DECL_SIZE (decl) = TYPE_SIZE (type);
DECL_SIZE_UNIT (decl) = TYPE_SIZE_UNIT (type);
}
else if (DECL_SIZE_UNIT (decl) == 0)
DECL_SIZE_UNIT (decl)
= fold_convert (sizetype, size_binop (CEIL_DIV_EXPR, DECL_SIZE (decl),
bitsize_unit_node));
if (code != FIELD_DECL)
/* For non-fields, update the alignment from the type. */
do_type_align (type, decl);
else
/* For fields, it's a bit more complicated... */
{
bool old_user_align = DECL_USER_ALIGN (decl);
bool zero_bitfield = false;
bool packed_p = DECL_PACKED (decl);
unsigned int mfa;
if (DECL_BIT_FIELD (decl))
{
DECL_BIT_FIELD_TYPE (decl) = type;
/* A zero-length bit-field affects the alignment of the next
field. In essence such bit-fields are not influenced by
any packing due to #pragma pack or attribute packed. */
if (integer_zerop (DECL_SIZE (decl))
&& ! targetm.ms_bitfield_layout_p (DECL_FIELD_CONTEXT (decl)))
{
zero_bitfield = true;
packed_p = false;
#ifdef PCC_BITFIELD_TYPE_MATTERS
if (PCC_BITFIELD_TYPE_MATTERS)
do_type_align (type, decl);
else
#endif
{
#ifdef EMPTY_FIELD_BOUNDARY
if (EMPTY_FIELD_BOUNDARY > DECL_ALIGN (decl))
{
DECL_ALIGN (decl) = EMPTY_FIELD_BOUNDARY;
DECL_USER_ALIGN (decl) = 0;
}
#endif
}
}
/* See if we can use an ordinary integer mode for a bit-field.
Conditions are: a fixed size that is correct for another mode
and occupying a complete byte or bytes on proper boundary. */
if (TYPE_SIZE (type) != 0
&& TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST
&& GET_MODE_CLASS (TYPE_MODE (type)) == MODE_INT)
{
enum machine_mode xmode
= mode_for_size_tree (DECL_SIZE (decl), MODE_INT, 1);
unsigned int xalign = GET_MODE_ALIGNMENT (xmode);
if (xmode != BLKmode
&& !(xalign > BITS_PER_UNIT && DECL_PACKED (decl))
&& (known_align == 0 || known_align >= xalign))
{
DECL_ALIGN (decl) = MAX (xalign, DECL_ALIGN (decl));
DECL_MODE (decl) = xmode;
DECL_BIT_FIELD (decl) = 0;
}
}
/* Turn off DECL_BIT_FIELD if we won't need it set. */
if (TYPE_MODE (type) == BLKmode && DECL_MODE (decl) == BLKmode
&& known_align >= TYPE_ALIGN (type)
&& DECL_ALIGN (decl) >= TYPE_ALIGN (type))
DECL_BIT_FIELD (decl) = 0;
}
else if (packed_p && DECL_USER_ALIGN (decl))
/* Don't touch DECL_ALIGN. For other packed fields, go ahead and
round up; we'll reduce it again below. We want packing to
supersede USER_ALIGN inherited from the type, but defer to
alignment explicitly specified on the field decl. */;
else
do_type_align (type, decl);
/* If the field is packed and not explicitly aligned, give it the
minimum alignment. Note that do_type_align may set
DECL_USER_ALIGN, so we need to check old_user_align instead. */
if (packed_p
&& !old_user_align)
DECL_ALIGN (decl) = MIN (DECL_ALIGN (decl), BITS_PER_UNIT);
if (! packed_p && ! DECL_USER_ALIGN (decl))
{
/* Some targets (i.e. i386, VMS) limit struct field alignment
to a lower boundary than alignment of variables unless
it was overridden by attribute aligned. */
#ifdef BIGGEST_FIELD_ALIGNMENT
DECL_ALIGN (decl)
= MIN (DECL_ALIGN (decl), (unsigned) BIGGEST_FIELD_ALIGNMENT);
#endif
#ifdef ADJUST_FIELD_ALIGN
DECL_ALIGN (decl) = ADJUST_FIELD_ALIGN (decl, DECL_ALIGN (decl));
#endif
}
if (zero_bitfield)
mfa = initial_max_fld_align * BITS_PER_UNIT;
else
mfa = maximum_field_alignment;
/* Should this be controlled by DECL_USER_ALIGN, too? */
if (mfa != 0)
DECL_ALIGN (decl) = MIN (DECL_ALIGN (decl), mfa);
}
/* Evaluate nonconstant size only once, either now or as soon as safe. */
if (DECL_SIZE (decl) != 0 && TREE_CODE (DECL_SIZE (decl)) != INTEGER_CST)
DECL_SIZE (decl) = variable_size (DECL_SIZE (decl));
if (DECL_SIZE_UNIT (decl) != 0
&& TREE_CODE (DECL_SIZE_UNIT (decl)) != INTEGER_CST)
DECL_SIZE_UNIT (decl) = variable_size (DECL_SIZE_UNIT (decl));
/* If requested, warn about definitions of large data objects. */
if (warn_larger_than
&& (code == VAR_DECL || code == PARM_DECL)
&& ! DECL_EXTERNAL (decl))
{
tree size = DECL_SIZE_UNIT (decl);
if (size != 0 && TREE_CODE (size) == INTEGER_CST
&& compare_tree_int (size, larger_than_size) > 0)
{
int size_as_int = TREE_INT_CST_LOW (size);
if (compare_tree_int (size, size_as_int) == 0)
warning (OPT_Wlarger_than_eq, "size of %q+D is %d bytes", decl, size_as_int);
else
warning (OPT_Wlarger_than_eq, "size of %q+D is larger than %wd bytes",
decl, larger_than_size);
}
}
/* If the RTL was already set, update its mode and mem attributes. */
if (rtl)
{
PUT_MODE (rtl, DECL_MODE (decl));
SET_DECL_RTL (decl, 0);
set_mem_attributes (rtl, decl, 1);
SET_DECL_RTL (decl, rtl);
}
}
/* Given a VAR_DECL, PARM_DECL or RESULT_DECL, clears the results of
a previous call to layout_decl and calls it again. */
void
relayout_decl (tree decl)
{
DECL_SIZE (decl) = DECL_SIZE_UNIT (decl) = 0;
DECL_MODE (decl) = VOIDmode;
if (!DECL_USER_ALIGN (decl))
DECL_ALIGN (decl) = 0;
SET_DECL_RTL (decl, 0);
layout_decl (decl, 0);
}
/* Begin laying out type T, which may be a RECORD_TYPE, UNION_TYPE, or
QUAL_UNION_TYPE. Return a pointer to a struct record_layout_info which
is to be passed to all other layout functions for this record. It is the
responsibility of the caller to call `free' for the storage returned.
Note that garbage collection is not permitted until we finish laying
out the record. */
record_layout_info
start_record_layout (tree t)
{
record_layout_info rli = XNEW (struct record_layout_info_s);
rli->t = t;
/* If the type has a minimum specified alignment (via an attribute
declaration, for example) use it -- otherwise, start with a
one-byte alignment. */
rli->record_align = MAX (BITS_PER_UNIT, TYPE_ALIGN (t));
rli->unpacked_align = rli->record_align;
rli->offset_align = MAX (rli->record_align, BIGGEST_ALIGNMENT);
#ifdef STRUCTURE_SIZE_BOUNDARY
/* Packed structures don't need to have minimum size. */
if (! TYPE_PACKED (t))
{
unsigned tmp;
/* #pragma pack overrides STRUCTURE_SIZE_BOUNDARY. */
tmp = (unsigned) STRUCTURE_SIZE_BOUNDARY;
if (maximum_field_alignment != 0)
tmp = MIN (tmp, maximum_field_alignment);
rli->record_align = MAX (rli->record_align, tmp);
}
#endif
rli->offset = size_zero_node;
rli->bitpos = bitsize_zero_node;
rli->prev_field = 0;
rli->pending_statics = 0;
rli->packed_maybe_necessary = 0;
rli->remaining_in_alignment = 0;
return rli;
}
/* These four routines perform computations that convert between
the offset/bitpos forms and byte and bit offsets. */
tree
bit_from_pos (tree offset, tree bitpos)
{
return size_binop (PLUS_EXPR, bitpos,
size_binop (MULT_EXPR,
fold_convert (bitsizetype, offset),
bitsize_unit_node));
}
tree
byte_from_pos (tree offset, tree bitpos)
{
return size_binop (PLUS_EXPR, offset,
fold_convert (sizetype,
size_binop (TRUNC_DIV_EXPR, bitpos,
bitsize_unit_node)));
}
void
pos_from_bit (tree *poffset, tree *pbitpos, unsigned int off_align,
tree pos)
{
*poffset = size_binop (MULT_EXPR,
fold_convert (sizetype,
size_binop (FLOOR_DIV_EXPR, pos,
bitsize_int (off_align))),
size_int (off_align / BITS_PER_UNIT));
*pbitpos = size_binop (FLOOR_MOD_EXPR, pos, bitsize_int (off_align));
}
/* Given a pointer to bit and byte offsets and an offset alignment,
normalize the offsets so they are within the alignment. */
void
normalize_offset (tree *poffset, tree *pbitpos, unsigned int off_align)
{
/* If the bit position is now larger than it should be, adjust it
downwards. */
if (compare_tree_int (*pbitpos, off_align) >= 0)
{
tree extra_aligns = size_binop (FLOOR_DIV_EXPR, *pbitpos,
bitsize_int (off_align));
*poffset
= size_binop (PLUS_EXPR, *poffset,
size_binop (MULT_EXPR,
fold_convert (sizetype, extra_aligns),
size_int (off_align / BITS_PER_UNIT)));
*pbitpos
= size_binop (FLOOR_MOD_EXPR, *pbitpos, bitsize_int (off_align));
}
}
/* Print debugging information about the information in RLI. */
void
debug_rli (record_layout_info rli)
{
print_node_brief (stderr, "type", rli->t, 0);
print_node_brief (stderr, "\noffset", rli->offset, 0);
print_node_brief (stderr, " bitpos", rli->bitpos, 0);
fprintf (stderr, "\naligns: rec = %u, unpack = %u, off = %u\n",
rli->record_align, rli->unpacked_align,
rli->offset_align);
/* The ms_struct code is the only that uses this. */
if (targetm.ms_bitfield_layout_p (rli->t))
fprintf (stderr, "remaining in alignment = %u\n", rli->remaining_in_alignment);
if (rli->packed_maybe_necessary)
fprintf (stderr, "packed may be necessary\n");
if (rli->pending_statics)
{
fprintf (stderr, "pending statics:\n");
debug_tree (rli->pending_statics);
}
}
/* Given an RLI with a possibly-incremented BITPOS, adjust OFFSET and
BITPOS if necessary to keep BITPOS below OFFSET_ALIGN. */
void
normalize_rli (record_layout_info rli)
{
normalize_offset (&rli->offset, &rli->bitpos, rli->offset_align);
}
/* Returns the size in bytes allocated so far. */
tree
rli_size_unit_so_far (record_layout_info rli)
{
return byte_from_pos (rli->offset, rli->bitpos);
}
/* Returns the size in bits allocated so far. */
tree
rli_size_so_far (record_layout_info rli)
{
return bit_from_pos (rli->offset, rli->bitpos);
}
/* FIELD is about to be added to RLI->T. The alignment (in bits) of
the next available location within the record is given by KNOWN_ALIGN.
Update the variable alignment fields in RLI, and return the alignment
to give the FIELD. */
unsigned int
update_alignment_for_field (record_layout_info rli, tree field,
unsigned int known_align)
{
/* The alignment required for FIELD. */
unsigned int desired_align;
/* The type of this field. */
tree type = TREE_TYPE (field);
/* True if the field was explicitly aligned by the user. */
bool user_align;
bool is_bitfield;
/* Do not attempt to align an ERROR_MARK node */
if (TREE_CODE (type) == ERROR_MARK)
return 0;
/* Lay out the field so we know what alignment it needs. */
layout_decl (field, known_align);
desired_align = DECL_ALIGN (field);
user_align = DECL_USER_ALIGN (field);
is_bitfield = (type != error_mark_node
&& DECL_BIT_FIELD_TYPE (field)
&& ! integer_zerop (TYPE_SIZE (type)));
/* Record must have at least as much alignment as any field.
Otherwise, the alignment of the field within the record is
meaningless. */
if (targetm.ms_bitfield_layout_p (rli->t))
{
/* Here, the alignment of the underlying type of a bitfield can
affect the alignment of a record; even a zero-sized field
can do this. The alignment should be to the alignment of
the type, except that for zero-size bitfields this only
applies if there was an immediately prior, nonzero-size
bitfield. (That's the way it is, experimentally.) */
if ((!is_bitfield && !DECL_PACKED (field))
|| (!integer_zerop (DECL_SIZE (field))
? !DECL_PACKED (field)
: (rli->prev_field
&& DECL_BIT_FIELD_TYPE (rli->prev_field)
&& ! integer_zerop (DECL_SIZE (rli->prev_field)))))
{
unsigned int type_align = TYPE_ALIGN (type);
type_align = MAX (type_align, desired_align);
if (maximum_field_alignment != 0)
type_align = MIN (type_align, maximum_field_alignment);
rli->record_align = MAX (rli->record_align, type_align);
rli->unpacked_align = MAX (rli->unpacked_align, TYPE_ALIGN (type));
}
}
#ifdef PCC_BITFIELD_TYPE_MATTERS
else if (is_bitfield && PCC_BITFIELD_TYPE_MATTERS)
{
/* Named bit-fields cause the entire structure to have the
alignment implied by their type. Some targets also apply the same
rules to unnamed bitfields. */
if (DECL_NAME (field) != 0
|| targetm.align_anon_bitfield ())
{
unsigned int type_align = TYPE_ALIGN (type);
#ifdef ADJUST_FIELD_ALIGN
if (! TYPE_USER_ALIGN (type))
type_align = ADJUST_FIELD_ALIGN (field, type_align);
#endif
/* Targets might chose to handle unnamed and hence possibly
zero-width bitfield. Those are not influenced by #pragmas
or packed attributes. */
if (integer_zerop (DECL_SIZE (field)))
{
if (initial_max_fld_align)
type_align = MIN (type_align,
initial_max_fld_align * BITS_PER_UNIT);
}
else if (maximum_field_alignment != 0)
type_align = MIN (type_align, maximum_field_alignment);
else if (DECL_PACKED (field))
type_align = MIN (type_align, BITS_PER_UNIT);
/* The alignment of the record is increased to the maximum
of the current alignment, the alignment indicated on the
field (i.e., the alignment specified by an __aligned__
attribute), and the alignment indicated by the type of
the field. */
rli->record_align = MAX (rli->record_align, desired_align);
rli->record_align = MAX (rli->record_align, type_align);
if (warn_packed)
rli->unpacked_align = MAX (rli->unpacked_align, TYPE_ALIGN (type));
user_align |= TYPE_USER_ALIGN (type);
}
}
#endif
else
{
rli->record_align = MAX (rli->record_align, desired_align);
rli->unpacked_align = MAX (rli->unpacked_align, TYPE_ALIGN (type));
}
TYPE_USER_ALIGN (rli->t) |= user_align;
return desired_align;
}
/* Called from place_field to handle unions. */
static void
place_union_field (record_layout_info rli, tree field)
{
update_alignment_for_field (rli, field, /*known_align=*/0);
DECL_FIELD_OFFSET (field) = size_zero_node;
DECL_FIELD_BIT_OFFSET (field) = bitsize_zero_node;
SET_DECL_OFFSET_ALIGN (field, BIGGEST_ALIGNMENT);
/* If this is an ERROR_MARK return *after* having set the
field at the start of the union. This helps when parsing
invalid fields. */
if (TREE_CODE (TREE_TYPE (field)) == ERROR_MARK)
return;
/* We assume the union's size will be a multiple of a byte so we don't
bother with BITPOS. */
if (TREE_CODE (rli->t) == UNION_TYPE)
rli->offset = size_binop (MAX_EXPR, rli->offset, DECL_SIZE_UNIT (field));
else if (TREE_CODE (rli->t) == QUAL_UNION_TYPE)
rli->offset = fold_build3 (COND_EXPR, sizetype,
DECL_QUALIFIER (field),
DECL_SIZE_UNIT (field), rli->offset);
}
#if defined (PCC_BITFIELD_TYPE_MATTERS) || defined (BITFIELD_NBYTES_LIMITED)
/* A bitfield of SIZE with a required access alignment of ALIGN is allocated
at BYTE_OFFSET / BIT_OFFSET. Return nonzero if the field would span more
units of alignment than the underlying TYPE. */
static int
excess_unit_span (HOST_WIDE_INT byte_offset, HOST_WIDE_INT bit_offset,
HOST_WIDE_INT size, HOST_WIDE_INT align, tree type)
{
/* Note that the calculation of OFFSET might overflow; we calculate it so
that we still get the right result as long as ALIGN is a power of two. */
unsigned HOST_WIDE_INT offset = byte_offset * BITS_PER_UNIT + bit_offset;
offset = offset % align;
return ((offset + size + align - 1) / align
> ((unsigned HOST_WIDE_INT) tree_low_cst (TYPE_SIZE (type), 1)
/ align));
}
#endif
/* RLI contains information about the layout of a RECORD_TYPE. FIELD
is a FIELD_DECL to be added after those fields already present in
T. (FIELD is not actually added to the TYPE_FIELDS list here;
callers that desire that behavior must manually perform that step.) */
void
place_field (record_layout_info rli, tree field)
{
/* The alignment required for FIELD. */
unsigned int desired_align;
/* The alignment FIELD would have if we just dropped it into the
record as it presently stands. */
unsigned int known_align;
unsigned int actual_align;
/* The type of this field. */
tree type = TREE_TYPE (field);
gcc_assert (TREE_CODE (field) != ERROR_MARK);
/* If FIELD is static, then treat it like a separate variable, not
really like a structure field. If it is a FUNCTION_DECL, it's a
method. In both cases, all we do is lay out the decl, and we do
it *after* the record is laid out. */
if (TREE_CODE (field) == VAR_DECL)
{
rli->pending_statics = tree_cons (NULL_TREE, field,
rli->pending_statics);
return;
}
/* Enumerators and enum types which are local to this class need not
be laid out. Likewise for initialized constant fields. */
else if (TREE_CODE (field) != FIELD_DECL)
return;
/* Unions are laid out very differently than records, so split
that code off to another function. */
else if (TREE_CODE (rli->t) != RECORD_TYPE)
{
place_union_field (rli, field);
return;
}
else if (TREE_CODE (type) == ERROR_MARK)
{
/* Place this field at the current allocation position, so we
maintain monotonicity. */
DECL_FIELD_OFFSET (field) = rli->offset;
DECL_FIELD_BIT_OFFSET (field) = rli->bitpos;
SET_DECL_OFFSET_ALIGN (field, rli->offset_align);
return;
}
/* Work out the known alignment so far. Note that A & (-A) is the
value of the least-significant bit in A that is one. */
if (! integer_zerop (rli->bitpos))
known_align = (tree_low_cst (rli->bitpos, 1)
& - tree_low_cst (rli->bitpos, 1));
else if (integer_zerop (rli->offset))
known_align = 0;
else if (host_integerp (rli->offset, 1))
known_align = (BITS_PER_UNIT
* (tree_low_cst (rli->offset, 1)
& - tree_low_cst (rli->offset, 1)));
else
known_align = rli->offset_align;
desired_align = update_alignment_for_field (rli, field, known_align);
if (known_align == 0)
known_align = MAX (BIGGEST_ALIGNMENT, rli->record_align);
if (warn_packed && DECL_PACKED (field))
{
if (known_align >= TYPE_ALIGN (type))
{
if (TYPE_ALIGN (type) > desired_align)
{
if (STRICT_ALIGNMENT)
warning (OPT_Wattributes, "packed attribute causes "
"inefficient alignment for %q+D", field);
else
warning (OPT_Wattributes, "packed attribute is "
"unnecessary for %q+D", field);
}
}
else
rli->packed_maybe_necessary = 1;
}
/* Does this field automatically have alignment it needs by virtue
of the fields that precede it and the record's own alignment?
We already align ms_struct fields, so don't re-align them. */
if (known_align < desired_align
&& !targetm.ms_bitfield_layout_p (rli->t))
{
/* No, we need to skip space before this field.
Bump the cumulative size to multiple of field alignment. */
warning (OPT_Wpadded, "padding struct to align %q+D", field);
/* If the alignment is still within offset_align, just align
the bit position. */
if (desired_align < rli->offset_align)
rli->bitpos = round_up (rli->bitpos, desired_align);
else
{
/* First adjust OFFSET by the partial bits, then align. */
rli->offset
= size_binop (PLUS_EXPR, rli->offset,
fold_convert (sizetype,
size_binop (CEIL_DIV_EXPR, rli->bitpos,
bitsize_unit_node)));
rli->bitpos = bitsize_zero_node;
rli->offset = round_up (rli->offset, desired_align / BITS_PER_UNIT);
}
if (! TREE_CONSTANT (rli->offset))
rli->offset_align = desired_align;
}
/* Handle compatibility with PCC. Note that if the record has any
variable-sized fields, we need not worry about compatibility. */
#ifdef PCC_BITFIELD_TYPE_MATTERS
if (PCC_BITFIELD_TYPE_MATTERS
&& ! targetm.ms_bitfield_layout_p (rli->t)
&& TREE_CODE (field) == FIELD_DECL
&& type != error_mark_node
&& DECL_BIT_FIELD (field)
&& (! DECL_PACKED (field)
/* Enter for these packed fields only to issue a warning. */
|| TYPE_ALIGN (type) <= BITS_PER_UNIT)
&& maximum_field_alignment == 0
&& ! integer_zerop (DECL_SIZE (field))
&& host_integerp (DECL_SIZE (field), 1)
&& host_integerp (rli->offset, 1)
&& host_integerp (TYPE_SIZE (type), 1))
{
unsigned int type_align = TYPE_ALIGN (type);
tree dsize = DECL_SIZE (field);
HOST_WIDE_INT field_size = tree_low_cst (dsize, 1);
HOST_WIDE_INT offset = tree_low_cst (rli->offset, 0);
HOST_WIDE_INT bit_offset = tree_low_cst (rli->bitpos, 0);
#ifdef ADJUST_FIELD_ALIGN
if (! TYPE_USER_ALIGN (type))
type_align = ADJUST_FIELD_ALIGN (field, type_align);
#endif
/* A bit field may not span more units of alignment of its type
than its type itself. Advance to next boundary if necessary. */
if (excess_unit_span (offset, bit_offset, field_size, type_align, type))
{
if (DECL_PACKED (field))
{
if (warn_packed_bitfield_compat == 1)
inform
(input_location,
"Offset of packed bit-field %qD has changed in GCC 4.4",
field);
}
else
rli->bitpos = round_up (rli->bitpos, type_align);
}
if (! DECL_PACKED (field))
TYPE_USER_ALIGN (rli->t) |= TYPE_USER_ALIGN (type);
}
#endif
#ifdef BITFIELD_NBYTES_LIMITED
if (BITFIELD_NBYTES_LIMITED
&& ! targetm.ms_bitfield_layout_p (rli->t)
&& TREE_CODE (field) == FIELD_DECL
&& type != error_mark_node
&& DECL_BIT_FIELD_TYPE (field)
&& ! DECL_PACKED (field)
&& ! integer_zerop (DECL_SIZE (field))
&& host_integerp (DECL_SIZE (field), 1)
&& host_integerp (rli->offset, 1)
&& host_integerp (TYPE_SIZE (type), 1))
{
unsigned int type_align = TYPE_ALIGN (type);
tree dsize = DECL_SIZE (field);
HOST_WIDE_INT field_size = tree_low_cst (dsize, 1);
HOST_WIDE_INT offset = tree_low_cst (rli->offset, 0);
HOST_WIDE_INT bit_offset = tree_low_cst (rli->bitpos, 0);
#ifdef ADJUST_FIELD_ALIGN
if (! TYPE_USER_ALIGN (type))