Handle attributes defined in terms of another

[Bernd Schmidt <bernds at codesourcery dot com>]

In a new port, I have

(define_attr "units62" "unknown,d,d_addr,l,m,s,dl,dls,ls"
  (const_string "unknown"))

(define_attr "units64" "unknown,d,d_addr,l,m,s,dl,dls,ls"
  (const_string "unknown"))

(define_attr "units" "unknown,d,d_addr,l,m,s,dl,dls,ls"
  (cond [(eq_attr "cpu" "c62x") (attr "units62")
	 (eq_attr "cpu" "c64x") (attr "units64")]
	(const_string "unknown")))

which is intended to allow each insn either to define a single "units"
attribute, or more specific "units62" and "units64" if there are
differences between CPUs.

Tests of the form (eq_attr "units" "something") fail in genattrtab.c,
since evaluate_eq_attr can e.g. end up with (attr "units62") in the
value, and it doesn't handle this.

I don't know this code very well.  I've copied a block of code from
elsewhere to look up attributes in this case.  That seems to work on the
port I'm working on, and it also bootstraps ok on i686-linux.  Ok?


Bernd

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