On Sun, Feb 12, 2023 at 04:11:58PM +0100, Julia Lawall wrote: > > > On Sun, 12 Feb 2023, Deepak R Varma wrote: > > > On Sat, Feb 11, 2023 at 03:25:03PM -0800, Bart Van Assche wrote: > > > On 2/7/23 03:54, Deepak R Varma wrote: > > > > When adding two bit-field mask values, an OR operation offers higher > > > > performance over an arithmetic operation. So, convert such addition to > > > > an OR based expression. > > > > > > Where is the evidence that supports this claim? On the following page I read > > > that there is no performance difference when using a modern CPU: https://cs.stackexchange.com/questions/75811/why-is-addition-as-fast-as-bit-wise-operations-in-modern-processors > > > > > > > Hello Bart, > > You are correct. Modern CPU designs have improved addition and the performance > > is at par with the bitwise operation. The document I had read earlier mentioned > > a performance improvement for old CPUs and microprocessors, which today is not > > the case. Thank you for sharing the link. > > > > > > Issue identified using orplus.cocci semantic patch script. > > > > > > Where is that script located? Can it be deleted such that submission of > > > patches similar to this patch stops? > > > > I have added Julia to this email to understand how to best use this semantic > > patch. I already discussed with her on improving the Semantic patch such that it > > doesn't suggest making change when constants are involved. > > FWIW, the semantic patch was never motivated by efficiency, but rather > with the goal of making the code more understandable. I think my interpretation of the patch log for [1] was not accurate. The line "Running time is divided by 3 ..." made me believe OR'ing would replace "F+A+R" instructions by a single operation. My bad. [1] https://lore.kernel.org/all/alpine.DEB.2.20.1711130649370.2483@hadrien/ > > julia
