[PATCH] Add custom lowering for add/sub with overflow ARM

[Tim Northover]

Hi Louis,

On 3 May 2014 01:43, Louis Gerbarg <lgg at apple.com> wrote:
> The attached patch provides custom lowering of overflow intrinsics for the ARM architecture.

As Pete said, a very good idea!

I think I'd prefer it if the tests also tracked data dependencies as
well as just the instructions used though. If you swapped some
operands around the results might be disastrous.

>         add     r2, r0, r1
>         mov     r1, #1
>         cmp     r2, r0
>         movvc   r1, #0

Couldn't this be simplified to:

        adds r2, r0, r1
        mov r1, #1
        movvc r1, #0

? This would probably involve adding ARMISD::ADDS and ARMISD::SUBS
nodes (see ARM64 for reference, it already has them).

Cheers.

Tim.