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
