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stor-layout.c (update_alignment_for_field): Correct handling of unnamed bitfields on PCC_BITFIELD_TYPE_MATTERS machines.

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* stor-layout.c (update_alignment_for_field): Correct handling of
	unnamed bitfields on PCC_BITFIELD_TYPE_MATTERS machines.
	* doc/tm.texi (PCC_BITFIELD_TYPE_MATTERS): Note that an unnamed
	bitfield does not affect alignment.

	* testsuite/gcc.dg/i386-bitfield3.c: New test.

From-SVN: r60439
This commit is contained in:
Mark Mitchell 2002-12-23 16:39:36 +00:00 • committed by Mark Mitchell
parent 7c02ae17fe
commit 8dc65b6e6d
5 changed files with 61 additions and 19 deletions
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7
gcc/ChangeLog
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@ -1,3 +1,10 @@
2002-12-23 Mark Mitchell <mark@codesourcery.com>
* stor-layout.c (update_alignment_for_field): Correct handling of
unnamed bitfields on PCC_BITFIELD_TYPE_MATTERS machines.
* doc/tm.texi (PCC_BITFIELD_TYPE_MATTERS): Note that an unnamed
bitfield does not affect alignment.
2002-12-23 David Edelsohn <edelsohn@gnu.org>
* expr.c (expand_assignment): Apply special treatment to

22
gcc/doc/tm.texi
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@ -1181,17 +1181,19 @@ go slower in that case, define this macro as 0.
Define this if you wish to imitate the way many other C compilers handle
alignment of bit-fields and the structures that contain them.
The behavior is that the type written for a bit-field (@code{int},
@code{short}, or other integer type) imposes an alignment for the
entire structure, as if the structure really did contain an ordinary
field of that type. In addition, the bit-field is placed within the
structure so that it would fit within such a field, not crossing a
boundary for it.
The behavior is that the type written for a named bit-field (@code{int},
@code{short}, or other integer type) imposes an alignment for the entire
structure, as if the structure really did contain an ordinary field of
that type. In addition, the bit-field is placed within the structure so
that it would fit within such a field, not crossing a boundary for it.
Thus, on most machines, a bit-field whose type is written as @code{int}
would not cross a four-byte boundary, and would force four-byte
alignment for the whole structure. (The alignment used may not be four
bytes; it is controlled by the other alignment parameters.)
Thus, on most machines, a named bit-field whose type is written as
@code{int} would not cross a four-byte boundary, and would force
four-byte alignment for the whole structure. (The alignment used may
not be four bytes; it is controlled by the other alignment parameters.)
An unnamed bit-field will not affect the alignment of the containing
structure.
If the macro is defined, its definition should be a C expression;
a nonzero value for the expression enables this behavior.

21
gcc/stor-layout.c
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@ -715,13 +715,9 @@ update_alignment_for_field (rli, field, known_align)
&& DECL_BIT_FIELD_TYPE (field)
&& ! integer_zerop (TYPE_SIZE (type)))
{
/* For these machines, a zero-length field does not
affect the alignment of the structure as a whole.
It does, however, affect the alignment of the next field
within the structure. */
if (! integer_zerop (DECL_SIZE (field)))
rli->record_align = MAX (rli->record_align, desired_align);
else if (! DECL_PACKED (field))
/* A zero-length bit-field affects the alignment of the next
field. */
if (!DECL_PACKED (field) && integer_zerop (DECL_SIZE (field)))
{
desired_align = TYPE_ALIGN (type);
#ifdef ADJUST_FIELD_ALIGN
@ -729,8 +725,8 @@ update_alignment_for_field (rli, field, known_align)
#endif
}
/* A named bit field of declared type `int'
forces the entire structure to have `int' alignment. */
/* Named bit-fields cause the entire structure to have the
alignment implied by their type. */
if (DECL_NAME (field) != 0)
{
unsigned int type_align = TYPE_ALIGN (type);
@ -745,7 +741,14 @@ update_alignment_for_field (rli, field, known_align)
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);
rli->unpadded_align = MAX (rli->unpadded_align, DECL_ALIGN (field));
if (warn_packed)
rli->unpacked_align = MAX (rli->unpacked_align, TYPE_ALIGN (type));

6
gcc/testsuite/ChangeLog
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@ -1,3 +1,9 @@
2002-12-23 Mark Mitchell <mark@codesourcery.com>
* testsuite/gcc.dg/i386-bitfield3.c: New test.
* testsuite/gcc.dg/i386-bitfield2.c: New test.
2002-12-22 Nathan Sidwell <nathan@codesourcery.com>
* g++.dg/parse/conv_op1.C: New test.

24
gcc/testsuite/gcc.dg/i386-bitfield3.c Normal file
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@ -0,0 +1,24 @@
// Test for bitfield alignment in structs on IA-32
// { dg-do run { target i?86-*-* } }
// { dg-options "-O2" }
// { dg-options "-mno-align-double -mno-ms-bitfields" { target *-*-interix* } }
extern void abort (void);
extern void exit (int);
struct X {
int : 32;
};
struct Y {
int i : 32;
};
int main () {
if (__alignof__(struct X) != 1)
abort ();
if (__alignof__(struct Y) != 4)
abort ();
exit (0);
}