[PATCH] blockfreq: Rewrite block frequency analysis

Chandler Carruth chandlerc at google.com
Wed Mar 19 13:45:56 PDT 2014

On Wed, Mar 19, 2014 at 1:38 PM, Duncan P. N. Exon Smith <
dexonsmith at apple.com> wrote:

> Does this sound good to everyone?

Well, I already said the basic cleanup patches were good.

I've not really had a chance to look at the algorithm in detail yet because

> Chandler, do you still want something up on Phab at some point?

... I was waiting for this before reviewing the algorithm in detail, so I
still haven't had a chance to do that. If using phab is slow, I can just go
through the patch files, I don't really care, it just seemed like i should
wait based on prior emails.

Currently, I'm somewhat skeptical of the benefit of PositiveFloat *for this
use case* (not in general), largely because of the comments about using
power-of-two loop trip scales. I actually don't understand why
distinguishing between a scale of 3 and 5 would be interesting at all. Do
we have any reason to believe either than our profiles will be this
accurate or that we will have transformations which are this sensitive? I
don't think either are true.

 If so, does it
> makes sense for me to post the current, massive, combined patch of
> 0003+0004+0005+0006(+0007?) now, so you can look at the algorithm as a
> whole?

I'm actually interested in evaluating this totally independent of the bias
part. I'm in complete agreement that the flow-solve aspect is orthogonal to
what precise metric is useful for triggering different optimizations.
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