[llvm] r185257 - InstCombine: Be more agressive optimizing 'udiv' instrs with 'select' denoms

[Chris Lattner]

On Jun 29, 2013, at 10:02 AM, David Majnemer <david.majnemer at gmail.com> wrote:

> I can check all the operands twice or just not do the transform. I don't readily see a nicer alternative but I am receptive to suggestions!
> 
> I figured that divides are worth annihilating with vigor due to how expensive they are and hoped they would be sufficiently uncommon that any wasted effort would be in the noise.

Eli is right though, this will burn compiler performance in cases that won't matter.  Remember that instcombine is run multiple times through the compiler flow.

> If its any consolation, this transform fires on LLVM itself.

Sounds like a great optimization, we just need a more efficient implementation :)

-Chris