[llvm-commits] [PATCH] Add the transformation ~(~X >>s Y) --> (X >>s Y)

[Jim Grosbach]

On Jan 19, 2010, at 8:36 AM, Edmund Grimley Evans wrote:

> Add this transformation in InstCombineAndOrXor.cpp:
> 
> ~(~X >>s Y) --> (X >>s Y)
> 
> It seems unlikely it could do any harm and it does have at least one
> use: together with other standard transformations it enables the
> following way of expressing an arithmetic shift right in portable C to
> be simplified into a single ASR operation:
> 
> int asr(int a, int b)
> {
>  return a < 0 ? -(-a - 1 >> b) - 1 : a >> b;
> }

Very nice! Thanks for the contribution.