tree.h (DECL_FIELD_OFFSET, [...]): Fix comments to reflect actual behavior and…

tree.h (DECL_FIELD_OFFSET, [...]): Fix comments to reflect actual behavior and relationship between...

2006-10-01  Sandra Loosemore  <sandra@codesourcery.com>

	* gcc/tree.h (DECL_FIELD_OFFSET, DECL_FIELD_BIT_OFFSET):  Fix
	comments to reflect actual behavior and relationship between
	DECL_FIELD_OFFSET, DECL_FIELD_BIT_OFFSET, and DECL_OFFSET_ALIGN.

	* gcc/doc/c-tree.texi (Working with declarations): Fix documentation
	of FIELD_DECL likewise.

From-SVN: r117352

gcc/ChangeLog

+2006-10-01  Sandra Loosemore  <sandra@codesourcery.com>
+
+	* tree.h (DECL_FIELD_OFFSET, DECL_FIELD_BIT_OFFSET):  Fix
+	comments to reflect actual behavior and relationship between
+	DECL_FIELD_OFFSET, DECL_FIELD_BIT_OFFSET, and DECL_OFFSET_ALIGN.
+
+	* doc/c-tree.texi (Working with declarations): Fix documentation
+	of FIELD_DECL likewise.
+
 2006-10-01  Ryan Mansfield  <rmansfield@qnx.com>
 
 	PR c/20533

gcc/doc/c-tree.texi

@@ -967,12 +967,20 @@ ordinary type might be @code{short} while the @code{DECL_ARG_TYPE} is
 
 @item FIELD_DECL
 These nodes represent non-static data members.  The @code{DECL_SIZE} and
-@code{DECL_ALIGN} behave as for @code{VAR_DECL} nodes.  The
-@code{DECL_FIELD_BITPOS} gives the first bit used for this field, as an
-@code{INTEGER_CST}.  These values are indexed from zero, where zero
-indicates the first bit in the object.
-
-If @code{DECL_C_BIT_FIELD} holds, this field is a bit-field.
+@code{DECL_ALIGN} behave as for @code{VAR_DECL} nodes.  
+The position of the field within the parent record is specified by a 
+combination of three attributes.  @code{DECL_FIELD_OFFSET} is the position,
+counting in bytes, of the @code{DECL_OFFSET_ALIGN}-bit sized word containing
+the bit of the field closest to the beginning of the structure.  
+@code{DECL_FIELD_BIT_OFFSET} is the bit offset of the first bit of the field
+within this word; this may be nonzero even for fields that are not bit-fields,
+since @code{DECL_OFFSET_ALIGN} may be greater than the natural alignment
+of the field's type.
+
+If @code{DECL_C_BIT_FIELD} holds, this field is a bit-field.  In a bit-field,
+@code{DECL_BIT_FIELD_TYPE} also contains the type that was originally
+specified for it, while DECL_TYPE may be a modified type with lesser precision,
+according to the size of the bit field.
 
 @item NAMESPACE_DECL
 @xref{Namespaces}.

gcc/tree.h

@@ -2648,11 +2648,14 @@ struct tree_decl_with_rtl GTY(())
 };
 
 /* In a FIELD_DECL, this is the field position, counting in bytes, of the
-   byte containing the bit closest to the beginning of the structure.  */
+   DECL_OFFSET_ALIGN-bit-sized word containing the bit closest to the beginning
+   of the structure.  */
 #define DECL_FIELD_OFFSET(NODE) (FIELD_DECL_CHECK (NODE)->field_decl.offset)
 
 /* In a FIELD_DECL, this is the offset, in bits, of the first bit of the
-   field from DECL_FIELD_OFFSET.  */
+   field from DECL_FIELD_OFFSET.  This field may be nonzero even for fields
+   that are not bit fields (since DECL_OFFSET_ALIGN may be larger than the
+   natural alignment of the field's type).  */
 #define DECL_FIELD_BIT_OFFSET(NODE) (FIELD_DECL_CHECK (NODE)->field_decl.bit_offset)
 
 /* In a FIELD_DECL, this indicates whether the field was a bit-field and