extend.texi (Common Type Attributes): Document vector_size.

gcc/ChangeLog:
	* doc/extend.texi (Common Type Attributes): Document vector_size.
	(Common Variable Attributes): Mention size constraint.  Correct
	quoting and typos.
	(Vector Extensions): Use @dfn when defining bas type.  Clarify
	base type and size constraints.

From-SVN: r269920

gcc/ChangeLog

+2019-03-25  Martin Sebor  <msebor@redhat.com>
+
+	* doc/extend.texi (Common Type Attributes): Document vector_size.
+	(Common Variable Attributes): Mention size constraint.  Correct
+	quoting and typos.
+	(Vector Extensions): Use @dfn when defining bas type.  Clarify
+	base type and size constraints.
+
 2019-03-25  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/89789

gcc/doc/extend.texi

@@ -7041,8 +7041,10 @@ class itself is instantiated.
 
 @item vector_size (@var{bytes})
 @cindex @code{vector_size} variable attribute
-This attribute specifies the vector size for the variable, measured in
-bytes.  For example, the declaration:
+This attribute specifies the vector size for the type of the declared
+variable, measured in bytes.  The type to which it applies is known as
+the @dfn{base type}.  The @var{bytes} argument must be a positive
+power-of-two multiple of the base type size.  For example, the declaration:
 
 @smallexample
 int foo __attribute__ ((vector_size (16)));
@@ -7050,10 +7052,12 @@ int foo __attribute__ ((vector_size (16)));
 
 @noindent
 causes the compiler to set the mode for @code{foo}, to be 16 bytes,
-divided into @code{int} sized units.  Assuming a 32-bit int (a vector of
-4 units of 4 bytes), the corresponding mode of @code{foo} is V4SI@.
+divided into @code{int} sized units.  Assuming a 32-bit @code{int},
+@code{foo}'s type is a vector of four units of four bytes each, and
+the corresponding mode of @code{foo} is @code{V4SI}.
+@xref{Vector Extensions} for details of manipulating vector variables.
 
-This attribute is only applicable to integral and float scalars,
+This attribute is only applicable to integral and floating scalars,
 although arrays, pointers, and function return values are allowed in
 conjunction with this construct.
 
@@ -8116,6 +8120,39 @@ the case with lock or thread classes, which are usually defined and then
 not referenced, but contain constructors and destructors that have
 nontrivial bookkeeping functions.
 
+@item vector_size (@var{bytes})
+@cindex @code{vector_size} type attribute
+This attribute specifies the vector size for the type, measured in bytes.
+The type to which it applies is known as the @dfn{base type}.  The @var{bytes}
+argument must be a positive power-of-two multiple of the base type size.  For
+example, the following declarations:
+
+@smallexample
+typedef __attribute__ ((vector_size (32))) int int_vec32_t ;
+typedef __attribute__ ((vector_size (32))) int* int_vec32_ptr_t;
+typedef __attribute__ ((vector_size (32))) int int_vec32_arr3_t[3];
+@end smallexample
+
+@noindent
+define @code{int_vec32_t} to be a 32-byte vector type composed of @code{int}
+sized units.  With @code{int} having a size of 4 bytes, the type defines
+a vector of eight units, four bytes each.  The mode of variables of type
+@code{int_vec32_t} is @code{V8SI}.  @code{int_vec32_ptr_t} is then defined
+to be a pointer to such a vector type, and @code{int_vec32_arr3_t} to be
+an array of three such vectors.  @xref{Vector Extensions} for details of
+manipulating objects of vector types.
+
+This attribute is only applicable to integral and floating scalar types.
+In function declarations the attribute applies to the function return
+type.
+
+For example, the following:
+@smallexample
+__attribute__ ((vector_size (16))) float get_flt_vec16 (void);
+@end smallexample
+declares @code{get_flt_vec16} to be a function returning a 16-byte vector
+with the base type @code{float}.
+
 @item visibility
 @cindex @code{visibility} type attribute
 In C++, attribute visibility (@pxref{Function Attributes}) can also be
@@ -10883,7 +10920,7 @@ typedef int v4si __attribute__ ((vector_size (16)));
 @end smallexample
 
 @noindent
-The @code{int} type specifies the base type, while the attribute specifies
+The @code{int} type specifies the @dfn{base type}, while the attribute specifies
 the vector size for the variable, measured in bytes.  For example, the
 declaration above causes the compiler to set the mode for the @code{v4si}
 type to be 16 bytes wide and divided into @code{int} sized units.  For
@@ -10891,9 +10928,9 @@ a 32-bit @code{int} this means a vector of 4 units of 4 bytes, and the
 corresponding mode of @code{foo} is @acronym{V4SI}.
 
 The @code{vector_size} attribute is only applicable to integral and
-float scalars, although arrays, pointers, and function return values
+floating scalars, although arrays, pointers, and function return values
 are allowed in conjunction with this construct. Only sizes that are
-a power of two are currently allowed.
+positive power-of-two multiples of the base type size are currently allowed.
 
 All the basic integer types can be used as base types, both as signed
 and as unsigned: @code{char}, @code{short}, @code{int}, @code{long},