[llvm-commits] More aggressive speculation in SimplifyCFG

[Chandler Carruth]

On Thu, Jan 24, 2013 at 4:31 PM, Hal Finkel <hfinkel at anl.gov> wrote:

> Chandler,
>
> Does your recent SimplifyCFG work affect this proposal?
>

Only a tiny bit.

My work was to remove some hard-coded assumptions, and manually rolled cost
models into thresholds and the TTI-based cost model. This shouldn't
significantly change how the code is SimplifyCFG works or the tradeoffs
LLVM makes. It continues to rely on something like early if-conversion for
forming anything but trivial predicated formations.

It should do two things (modulo bugs of course):
1) It makes the existing "if-conversion"-like functionality in SimplifyCFG
both more correct and consistent. It will no longer fail to convert equally
trivial constructs, and it will no longer mistakenly convert expensive
constructs.

2) It makes the mechanism for the transformation itself a bit more flexible
and robust, so that *if* we ever have a reason to do more of this in the
IR, the code can actually handle it.


I still thing it is worth investigating the pattern I described, and I
think Dan is thinking about some of these issues.... But there are still
some hard problems to solve to make it feasible & profitable. =]
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130124/69113f38/attachment.html>