[LLVMdev] PBQP & register pairing

[Jakob Stoklund Olesen]

On Jun 6, 2011, at 12:14 PM, Peter Lawrence wrote:

> Arnaud,
>                another way to look at it, if the description of your register sets includes "pairs",
> is that your assembly language syntax for MPQD is redundant, operand-2 is the second
> half of the register-pair in operand-0,  so an alternative is to let llvm think this is a two
> operand instruction (one of them being a pair) rather than a three operand instruction.
> 
> even if you are not currently defining pairs in your register definitions, it might be less work
> to do that than to write and add an extra new pass.  Many many target machines have some
> notion of register pairs, so it should not be too hard to find examples of how to do this.

ARM's QQ and QQQQ register classes are examples.

It is currently a bit tedious to specify these constraints; cleaning that up is on my todo list.

/jakob