[llvm-dev] nuw, nsw flags for SCEVAdd and SCEVMul

[Sanjoy Das via llvm-dev]

I think what you suggest would be a correct enhancement to SCEV, but I
thought Tim [CCed] already fixed this in
https://reviews.llvm.org/rL336140.

-- Sanjoy
On Tue, Aug 14, 2018 at 4:28 AM Lin-Ya Yu via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> Hi,
>
> I found out that we do not have nuw and nsw flags for some situations. I ran test cases with range metadata: !2 = !{i16 0, i16 128}
>
> And I get nuw, nsw flags for
>
>   %A = add i16 %x, 2
>   -->  (2 + %x)<nuw><nsw> U: [2,130) S: [2,130)
>
> But for below cases, there are no nuw or nsw flags shown.
>
>   %A = add i16 %x, %x
>   -->  (2 * %x) U: [0,255) S: [0,255)
>
>   %A = mul i16 %x, 2
>   -->  (2 * %x) U: [0,255) S: [0,255)
>
>   %A = mul i16 %x, %x
>   -->  (%x * %x) U: [0,16130) S: [0,16130)
>
> From the range we calculated here. Can't we have the flags?
>
> And for instructions with nuw, I still did not get those flags.
>   %A = mul nuw i16 %x, %x
>   -->  (%x * %x) U: [0,16130) S: [0,16130)
>
>   %A = add nuw i16 %x, %x
>   -->  (2 * %x) U: [0,255) S: [0,255)
>
> Are there any reasons for this behavior? Or is it okay to have those flags for cases mentioned above?
>
> Thanks,
> Lin-Ya
>
> --
> From: yu810226 at gmail.com
> 于琳雅 (Lin-Ya Yu)
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev