Next: Examples, Previous: Defining Mode Macros, Up: Mode Macros
If an .md file construct uses mode macros, each version of the construct will often need slightly different strings. For example:
define_expand defines several addm3 patterns
(see Standard Names), each expander will need to use the
appropriate mode name for m.
define_insn defines several instruction patterns,
each instruction will often use a different assembler mnemonic.
GCC supports such variations through a system of “mode attributes”.
There are two standard attributes: mode, which is the name of
the mode in lower case, and MODE, which is the same thing in
upper case. You can define other attributes using:
(define_mode_attr name [(mode1 "value1") ... (moden "valuen")])
where name is the name of the attribute and valuei is the value associated with modei.
When GCC replaces some :macro with :mode, it will
scan each string in the pattern for sequences of the form
<macro:attr>, where attr is the name of
a mode attribute. If the attribute is defined for mode, the
whole <...> sequence will be replaced by the appropriate
attribute value.
For example, suppose an .md file has:
(define_mode_macro P [(SI "Pmode == SImode") (DI "Pmode == DImode")])
(define_mode_attr load [(SI "lw") (DI "ld")])
If one of the patterns that uses :P contains the string
"<P:load>\t%0,%1", the SI version of that pattern
will use "lw\t%0,%1" and the DI version will use
"ld\t%0,%1".
The macro: prefix may be omitted, in which case the
substitution will be attempted for every macro expansion.