[llvm-commits] [PATCH] Make EarlyCSE understand commutativity

[Owen Anderson]

On Oct 1, 2012, at 10:42 AM, Chris Lattner <clattner at apple.com> wrote:

> 
> On Sep 30, 2012, at 7:07 PM, Michael Ilseman <milseman at apple.com> wrote:
> 
>> Attached is a new version. I went with "CanonicalExpr" and added function level comments.
> 
> Hi Michael,
> 
> Why is this needed?  Why isn't it enough to change the predicate in "DenseMapInfo<SimpleValue>::isEqual" to handle commutative operations?

I don't think that's sufficient.  isEqual is used to resolve collisions.  It won't help here, because the commuted instructions will hash to different values up front.  Note that after reassociation we could rely on  commuted (integer) instructions being canonicalized, but that doesn't help given EarlyCSE's place in the pipeline.

--Owen