[PATCH] D28219: [X86] Attempt to pre-truncate arithmetic operations if useful

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon marked an inline comment as done.
RKSimon added a comment.

In https://reviews.llvm.org/D28219#633779, @delena wrote:

> One some targets pmulld is significantly slower than pmullw (FeatureSlowPMULLD). I assume that truncating even different (variable) inputs should be profitable in this case.
>
> And your transformation may be profitable for this scenario:
>
> trunc(binop (s/zext(x), s/zext(y)) when x and y are different variables.


If its alright, I can add support for both of these in followup patches. I've added TODOs to describe possible areas for improvement.


Repository:
  rL LLVM

https://reviews.llvm.org/D28219