re PR middle-end/22275 (bitfield layout change)
PR middle-end/22275
* stor-layout.c (layout_decl): Zero-width bitfields aren't
influenced by maximum_field_alignment or DECL_PACKED.
(update_alignment_for_field): Ditto.
(place_field): Ditto.
* doc/extend.texi (<#pragma pack>, <Type Attributes>): Document
this behaviour.
From-SVN: r111109
This commit is contained in:
Michael Matz
Michael Matz
parent
b98e315984
commit
d1a701eb17
3 changed files with 51 additions and 17 deletions
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@ -1,3 +1,14 @@
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2006-02-15 Michael Matz <matz@suse.de>
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PR middle-end/22275
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* stor-layout.c (layout_decl): Zero-width bitfields aren't
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influenced by maximum_field_alignment or DECL_PACKED.
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(update_alignment_for_field): Ditto.
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(place_field): Ditto.
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* doc/extend.texi (<#pragma pack>, <Type Attributes>): Document
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this behaviour.
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2006-02-15 Paolo Bonzini <bonzini@gnu.org>
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* cfg.c (dump_flow_info): Get dump flags as an additional parameter.
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@ -3329,9 +3329,10 @@ alignment. See your linker documentation for further information.
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@item packed
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This attribute, attached to @code{struct} or @code{union} type
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definition, specifies that each member of the structure or union is
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placed to minimize the memory required. When attached to an @code{enum}
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definition, it indicates that the smallest integral type should be used.
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definition, specifies that each member (other than zero-width bitfields)
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of the structure or union is placed to minimize the memory required. When
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attached to an @code{enum} definition, it indicates that the smallest
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integral type should be used.
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@opindex fshort-enums
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Specifying this attribute for @code{struct} and @code{union} types is
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@ -9518,10 +9519,10 @@ way of knowing that that happened.)
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@subsection Structure-Packing Pragmas
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For compatibility with Win32, GCC supports a set of @code{#pragma}
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directives which change the maximum alignment of members of structures,
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unions, and classes subsequently defined. The @var{n} value below always
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is required to be a small power of two and specifies the new alignment
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in bytes.
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directives which change the maximum alignment of members of structures
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(other than zero-width bitfields), unions, and classes subsequently
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defined. The @var{n} value below always is required to be a small power
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of two and specifies the new alignment in bytes.
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@enumerate
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@item @code{#pragma pack(@var{n})} simply sets the new alignment.
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@ -339,17 +339,22 @@ layout_decl (tree decl, unsigned int known_align)
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/* For fields, it's a bit more complicated... */
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{
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bool old_user_align = DECL_USER_ALIGN (decl);
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bool zero_bitfield = false;
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bool packed_p = DECL_PACKED (decl);
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unsigned int mfa;
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if (DECL_BIT_FIELD (decl))
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{
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DECL_BIT_FIELD_TYPE (decl) = type;
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/* A zero-length bit-field affects the alignment of the next
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field. */
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field. In essence such bit-fields are not influenced by
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any packing due to #pragma pack or attribute packed. */
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if (integer_zerop (DECL_SIZE (decl))
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&& ! DECL_PACKED (decl)
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&& ! targetm.ms_bitfield_layout_p (DECL_FIELD_CONTEXT (decl)))
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{
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zero_bitfield = true;
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packed_p = false;
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#ifdef PCC_BITFIELD_TYPE_MATTERS
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if (PCC_BITFIELD_TYPE_MATTERS)
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do_type_align (type, decl);
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@ -393,7 +398,7 @@ layout_decl (tree decl, unsigned int known_align)
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&& DECL_ALIGN (decl) >= TYPE_ALIGN (type))
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DECL_BIT_FIELD (decl) = 0;
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}
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else if (DECL_PACKED (decl) && DECL_USER_ALIGN (decl))
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else if (packed_p && DECL_USER_ALIGN (decl))
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/* Don't touch DECL_ALIGN. For other packed fields, go ahead and
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round up; we'll reduce it again below. We want packing to
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supersede USER_ALIGN inherited from the type, but defer to
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@ -408,14 +413,14 @@ layout_decl (tree decl, unsigned int known_align)
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Note that do_type_align may set DECL_USER_ALIGN, so we need to
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check old_user_align instead. */
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if (DECL_PACKED (decl)
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if (packed_p
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&& !old_user_align
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&& (DECL_NONADDRESSABLE_P (decl)
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|| DECL_SIZE_UNIT (decl) == 0
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|| TREE_CODE (DECL_SIZE_UNIT (decl)) == INTEGER_CST))
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DECL_ALIGN (decl) = MIN (DECL_ALIGN (decl), BITS_PER_UNIT);
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if (! DECL_USER_ALIGN (decl) && ! DECL_PACKED (decl))
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if (! packed_p && ! DECL_USER_ALIGN (decl))
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{
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/* Some targets (i.e. i386, VMS) limit struct field alignment
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to a lower boundary than alignment of variables unless
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@ -429,9 +434,13 @@ layout_decl (tree decl, unsigned int known_align)
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#endif
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}
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if (zero_bitfield)
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mfa = initial_max_fld_align * BITS_PER_UNIT;
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else
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mfa = maximum_field_alignment;
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/* Should this be controlled by DECL_USER_ALIGN, too? */
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if (maximum_field_alignment != 0)
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DECL_ALIGN (decl) = MIN (DECL_ALIGN (decl), maximum_field_alignment);
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if (mfa != 0)
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DECL_ALIGN (decl) = MIN (DECL_ALIGN (decl), mfa);
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}
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/* Evaluate nonconstant size only once, either now or as soon as safe. */
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@ -715,7 +724,16 @@ update_alignment_for_field (record_layout_info rli, tree field,
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type_align = ADJUST_FIELD_ALIGN (field, type_align);
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#endif
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if (maximum_field_alignment != 0)
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/* Targets might chose to handle unnamed and hence possibly
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zero-width bitfield. Those are not influenced by #pragmas
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or packed attributes. */
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if (integer_zerop (DECL_SIZE (field)))
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{
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if (initial_max_fld_align)
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type_align = MIN (type_align,
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initial_max_fld_align * BITS_PER_UNIT);
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}
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else if (maximum_field_alignment != 0)
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type_align = MIN (type_align, maximum_field_alignment);
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else if (DECL_PACKED (field))
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type_align = MIN (type_align, BITS_PER_UNIT);
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@ -1177,6 +1195,10 @@ place_field (record_layout_info rli, tree field)
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if (DECL_BIT_FIELD_TYPE (field))
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{
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unsigned int type_align = TYPE_ALIGN (type);
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unsigned int mfa = maximum_field_alignment;
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if (integer_zerop (DECL_SIZE (field)))
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mfa = initial_max_fld_align * BITS_PER_UNIT;
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/* Only the MS bitfields use this. We used to also put any kind of
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packed bit fields into prev_field, but that makes no sense, because
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@ -1185,8 +1207,8 @@ place_field (record_layout_info rli, tree field)
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are also not fulfilled.
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There is no sane value to set rli->remaining_in_alignment to when
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a packed bitfield in prev_field is unaligned. */
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if (maximum_field_alignment != 0)
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type_align = MIN (type_align, maximum_field_alignment);
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if (mfa != 0)
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type_align = MIN (type_align, mfa);
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gcc_assert (rli->prev_field
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|| actual_align >= type_align || DECL_PACKED (field)
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|| integer_zerop (DECL_SIZE (field))
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