llvm dev - Oct 2021 - The select story

Hello all,

In early 2021, a transformation in InstCombine that folds 'select i1 %a, i1
%b, i1 false' to 'and i1 %a, %b' (and another one for the
'or' case as
well) was removed because the folding was incorrect.

To explain the background about this change and a series of patches that
were made, I wrote a blog post:
https://aqjune.github.io/posts/2021-10-4.the-select-story.html

I appreciate many people who helped fix it! :)

Sincerely,
Juneyoung
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My complements both on an informative writeup, and the completion of a 
long and complicated effort.  Thank you (and others) for all the work on 
this.

Philip

On 10/4/21 6:19 AM, Juneyoung Lee via llvm-dev wrote:
> Hello all,
>
> In early 2021, a transformation in InstCombine that folds 'select i1 
> %a, i1 %b, i1 false' to 'and i1 %a, %b' (and another one for
the 'or'
> case as well) was removed because the folding was incorrect.
>
> To explain the background about this change and a series of patches 
> that were made, I wrote a blog post:
> https://aqjune.github.io/posts/2021-10-4.the-select-story.html 
> <https://aqjune.github.io/posts/2021-10-4.the-select-story.html>
>
> I appreciate many people who helped fix it! :)
>
> Sincerely,
> Juneyoung
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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