Re: Insn canonicalization not only with constant

[Sami Khawam <S dot Khawam at ee dot ed dot ac dot uk>]

>    OK, I see what you mean. The reason you can get both (ior (ashift ...)
> (lshiftrt ...)) and (ior (lshiftrt ...) (ashift ...)) is that simplify-rtx.c
> has no rule to canonicalize such expressions and that LSHIFTRT and
> ASHIFT have the same precedence.
>
>    Hmm, in simplify_binary_operation_1(), it says:
>
>       /* Convert (ior (ashift A CX) (lshiftrt A CY)) where CX+CY equals the
>          mode size to (rotate A CX).  */

ok, so that means that in that specific shift example I could go away 
with a rotate operation (even though it has to be of mode DI -> SI).

>    Right after that is code to make sure ASHIFT is the first operand for the
> simplification attempts that follow. You could try adding code to do this in
> general, but I don't know where such code should be added.

I will look more into this. It might be that there is no simple way to 
activate canonicalization for the general case (i.e. any insn that 
defined in the machine description), and maybe it has to be done to 
every specific type of operation.

>    Btw, I found this in rtlanal.c:
>
> int
> commutative_operand_precedence (rtx op)
>   :
>   :

It seems like commutative_operand_precedence() is only used twice to 
swap operand1 and operand2 - so the fact that it returns low values (or 
high, since the comment in the code seems wrong) for general operands 
shouldn't affect the ability to canonicalize them.

Sami