[llvm-dev] Getting up to speed with llvm backends. Machine Instruction operands.

[David Greene via llvm-dev]

David Greene via llvm-dev <llvm-dev at lists.llvm.org> writes:

>> I ask because the backend I would like to target the Hitachi/Motorola
>> 6309/6809 which too provides dedicated indexing (addressing)
>> registers. In fact in all binary operations the second operand is
>> either immediate or some kind of a memory reference via a
>> index/address register.
>
> I'm not familiar with this architecture, but I will try to answer
> question as best I can.

I missed this the first time around so I'll add it now.

Special index/address registers are really no problem.  They're just a
different register class.  There are target hooks you would redefine to
implement copying between registers of different classes when the code
generator realizes the value it needs is in the "wrong" register class.
It *should* mostly just fall out given correct register class
definitions and typing the TableGen pattern inputs correctly.

I think the concern raised by the thesis paper is very specific to
calling convention.  The TriCore ABI apparently requires that
arguments/return values of pointer and integer type be passed in
different register classes.  Does your target have a similar
requirement?  If not, then I don't think you have anything to worry
about.

                     -David