[PATCH] Transform C - zext(bool) -> bool ? C - 1 : C

[Nick Lewycky]

Hi Evan, this is about your r159230,
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20120625/145470.html.
The canonicalization was added, then removed by you. In post-commit
review, Eli asked you to pick one of the two forms to be canonical.

I have no problem with David landing this patch as is -- it looks like
goodness to me, particularly the "C - zext(X)" transform -- but I don't
want to mess you up. Could you please chime in?

Nick


On 12 July 2013 16:03, David Majnemer <david.majnemer at gmail.com> wrote:

> The attached patch essentially reverts r159230.
>
> The reasons why are because:
> 1. It creates an asymmetry in the IR by hurting our ability to
> canonicalize things like C - zext(X) and C + zext(!X) into the same thing.
> 2. Adding it back does not break any tests and without it we still
> generate the inferior code mentioned in the commit log.
>
> It seems like we should keep the canonicalization and fix (the apparently
> still broken problem) in the lowering stage.
> The commit mentioned that some targets don't have a sext i1. This
> shouldn't be a concern at the IR level, should it?
>
> --
> David Majnemer
>
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