[PATCH] [InstCombineAddSub] Added the transformation - "sub (or A B) (xor A B) -> (and A B)"

[Sean Silva]

On Sat, Oct 18, 2014 at 2:47 AM, David Majnemer <david.majnemer at gmail.com>
wrote:

> InstCombine is not supposed to handle every possible just because it is
> theoretically possible case.  It's engineered to be a series of engineering
> tradeoffs.  I don't know what the history of the similar transform is in
> VisitAdd, it's possible that it wasn't added in a principled way.
>

IIRC I did a cursory look at the blame and it was actually you who showed
up for the corresponding transform in VisitAdd. Or maybe you were
committing a patch for someone? Probably worth taking a look at the log to
see if you remember.

-- Sean Silva


>
> If we were to arbitrarily add patterns, we would eventually make
> InstCombine cripplingly slow.
>
> http://reviews.llvm.org/D5719
>
>
>
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