[PATCH] Early Target Dependent DAG Combine

[Quentin Colombet]

Thanks Dan for the big picture.

I'll give up on that patch for now.

-Quentin

On Jan 30, 2013, at 2:13 PM, Dan Gohman <dan433584 at gmail.com> wrote:

> 
> 
> On Wed, Jan 30, 2013 at 1:56 PM, Quentin Colombet <qcolombet at apple.com> wrote:
> Hi Dan,
> 
> Thanks for the review.
> 
> In fact, I'm already aware of the problem you are reporting, i.e., instcombine disrupts the BFI pattern.
> I'm not trying to fix this issue here.
> 
> Instead, I was trying to expose the kind of thing that can be achieved with the proposed hook using an in-tree target. 
> 
> Unfortunately, I don't know enough the existing problems for in-tree targets to come with a better example, but I'm sure somebody else run into this kind of problems and the proposed hook could have ease their development.
> 
> What do you think of the proposed hook?
> 
> In the abstract, it's counter to dagcombine's design. Dagcombine is designed to make use of canonicalization, in a similar fashion to instcombine. Opening up a mechanism to let targets make exceptions to this rule opens up a new kind of potential complexity. And, it adds yet another context to the already-known-to-be-confusing set of contexts in which target hooks can be called.
> 
> I don't think dagcombine's current design needs to remain fixed, however changing it really ought to be done with a clear motivation.
> 
> Dan
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130130/9ff8679d/attachment.html>