🚀 go-pugleaf

The Scond instructions are very useful - they set
a value to 0 if a condition is false or a constant
if the condition is true.  My problem is this:

1) The constant that you set when true is picked at
compile time - I used 1.  However the way which I
code the Scond instructions mean that I can place
a wide variety of constants into the true and false
arms very easily.

2) I could also make the result equal one of two registers - this
sounds useful for things like a=b?c:d

3) There is the case of code such as:
if (cond)
  a=b

What define_insn or define_expand etc. do I have to do to pick up 2, and 3
and is there a way of making a more flexible (1).

The approach I tried was to add definitions of the form:
(define_insn ""
  [(set (match_operand:SI 0 "register_operand" "=r,=r,=r,=r")
  (if_then_else (eq (cc0) (const_int 0))
	(match_operand:SI 1 "predicate" "r,I,r,I")
      (match_operand:SI 2 "predicate" "r,r,I,I")))]
  ""
  "*
   output_asm_insn etc.
")

But it completely ignores these!  Is there any way I can tell why - is it
my constraints/my predicates/ or am I doing something more seriously wrong?

My main interest in this comes from the dhrystone program which has a comparison
on a character variable and if it succeeds has Int_Loc=7. gcc presently
ends up using an 'sgtu' rule and a load of anding and oring - in actual
fact it was a LOT more compact with out the sgtu definitions in!

Any help on this would be greatly appreciated.

Dave


P.S. I know this is a little basic, but can someone give me an absolute
definition of when define_insn, and define_expand should be used.  I think
I am write in thinking define_expand is for producing new bits of rtl,
but often you see that these just end up producing new specialist instructions
which are trapped as a new instruction.

--
-------------------------------------------------------------------------------
- David Alan Gilbert - gilbertd@cs.man.ac.uk - G7FHJ@GB7CRG                   -
------(Programmers don't sleep - they just park their heads)-------------------