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(gcc-295.info)Defining Attributes

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Defining Attributes and their Values
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   The `define_attr' expression is used to define each attribute
required by the target machine.  It looks like:

     (define_attr NAME LIST-OF-VALUES DEFAULT)

   NAME is a string specifying the name of the attribute being defined.

   LIST-OF-VALUES is either a string that specifies a comma-separated
list of values that can be assigned to the attribute, or a null string
to indicate that the attribute takes numeric values.

   DEFAULT is an attribute expression that gives the value of this
attribute for insns that match patterns whose definition does not
include an explicit value for this attribute.  Note: Attr Example,
for more information on the handling of defaults.  Note: Constant
Attributes, for information on attributes that do not depend on any
particular insn.

   For each defined attribute, a number of definitions are written to
the `insn-attr.h' file.  For cases where an explicit set of values is
specified for an attribute, the following are defined:

   * A `#define' is written for the symbol `HAVE_ATTR_NAME'.

   * An enumeral class is defined for `attr_NAME' with elements of the
     form `UPPER-NAME_UPPER-VALUE' where the attribute name and value
     are first converted to upper case.

   * A function `get_attr_NAME' is defined that is passed an insn and
     returns the attribute value for that insn.

   For example, if the following is present in the `md' file:

     (define_attr "type" "branch,fp,load,store,arith" ...)

the following lines will be written to the file `insn-attr.h'.

     #define HAVE_ATTR_type
     enum attr_type {TYPE_BRANCH, TYPE_FP, TYPE_LOAD,
                      TYPE_STORE, TYPE_ARITH};
     extern enum attr_type get_attr_type ();

   If the attribute takes numeric values, no `enum' type will be
defined and the function to obtain the attribute's value will return
`int'.