[LLVMdev] rol/ror llvm instruction set

[Kasra]

--- On Tue, 2/3/09, Bill Wendling <isanbard at gmail.com> wrote:

> From: Bill Wendling <isanbard at gmail.com>
> Subject: Re: [LLVMdev] rol/ror llvm instruction set
> To: "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>
> Cc: kasra_n500 at yahoo.com
> Date: Tuesday, February 3, 2009, 2:52 PM
> On Tue, Feb 3, 2009 at 2:45 PM, Dale Johannesen
> <dalej at apple.com> wrote:
> >
> > On Feb 3, 2009, at 2:35 PMPST, Mike Stump wrote:
> >
> >> On Feb 3, 2009, at 2:28 PM, Kasra wrote:
> >>> I was looking around the LLVM instruction set
> and I failed to find
> >>> ROL and ROR instructions. Is there any plans
> on adding these
> >>> instructions to LLVM?
> >>
> >> Not sure what you mean:
> >
> > He's referring to the LLVM IR, I think, and
> it's true that doesn't
> > have rotates.  The LLVM back ends do know about rotate
> instructions on
> > targets that have them, though, and the llvm
> optimizers are pretty
> > smart about recognizing the usual ways to express
> rotate with shift/
> > and/or, as below.
> >
> Look in the DAGCombiner.cpp file to see which patterns it
> translates
> into ROTL and ROTR instructions.
> 
> -bw

I guess the backends could know about the instructions. But I am not convinced why it is beneficial not to have ROR and ROL instructions within llvm.


> Look in the DAGCombiner.cpp file to see which patterns it
> translates
> into ROTL and ROTR instructions.

Right, I sure will do.

-- Kasra