[llvm-dev] [RFC] Disabling DAG combines in /O0

[Pete Cooper via llvm-dev]

Sent from my iPhone

> On May 17, 2016, at 6:39 PM, Chandler Carruth via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> My question is: is it worth that in the face of progress towards global isel? I'm not sure it is, but I'm also not sure it isn't. =/ this seems to be a hard tradeoff question.
I wondered the same. GlobalISel is going to have to reimplement pretty much everything a backend has in order to be equivalent. 

It would certainly make life easier if 'SelectionDag -O0' only did lowering, legalisation and selection with no combines (and possibly no canonicalisation) as then 'GlobalIsel -O0' can get equivalence much sooner. Also makes diffing their outputs at -O0 much easier. And then diffing again at -O1 to see what else is missing to match outputs there.

Pete