[LLVMdev] Tablegen: How to define an instruction that reads and writes the same register

[Eli Friedman]

On Thu, Jan 19, 2012 at 6:07 PM, Tom Stellard <thomas.stellard at amd.com> wrote:
> Hi,
>
> Is it possible to define an Instruction with tablegen that reads and
> writes the same register?  For example, an increment instruction that
> reads a value from a register, adds one to it and then writes the result
> back to the same register.

Yes; you just write the instruction as if the dest and src are
distinct, then specify 'let Constraints = "$src1 = $dst"'.  See for
example INC32r in the x86 backend.

-Eli