[LLVMdev] [llvm-commits] rotate

[Eli Friedman]

On Tue, Jul 31, 2012 at 8:42 AM, Cameron McInally
<cameron.mcinally at nyu.edu> wrote:
> Andy,
>
> Here is the left circular shift operator patch. I apologize to the reviewer
> in advance. The patch has a good bit of fine detail. Any
> comments/criticisms?
>
> Some caveats...
>
> 1) This is just the bare minimum needed to make the left circular shift
> operator work (e.g. no instruction combining).
>
> 2) I tried my best to select operator names in the existing style; please
> feel free to change them as appropriate.

We intentionally haven't included a rotate instruction in LLVM in the
past; the justification is that it's generally straightforward for the
backend to form rotate operations, and making the optimizer
effectively handle the new rotation instruction adds a substantial
amount of complexity.  You're going to need to make a strong argument
that the current approach is insufficient if you want to commit a
patch like this.

-Eli