[LLVMdev] RFC: Binary format for instrumentation based profiling data

[Chandler Carruth]

On Fri, Apr 18, 2014 at 12:22 PM, Evan Cheng <evan.cheng at apple.com> wrote:

> I agree the top priority should always be "getting it right”. But I can’t
> agree with this thinking completely. This has to be balanced with
> pragmatism. If we completely disregard the practical concerns of commercial
> use, it makes LLVM hostile towards an important group of users.


Clearly, I can't argue with that. =] We benefit from it as well. And I
don't think I'm arguing against a pragmatic approach in this case, although
I'm sorry if it comes off that way.

Just so we're on the same page, the only real question in my mind is: can
we make breaking changes as we iterate on the design.

What I would like to do is figure out the right design first,
incrementally, trying one format, and seeing how it does, but potentially
with backwards incompatible changes. Once we have the experience and know
what the right format is, *then* we should consider pragmatic concerns such
as how to structure support for reading legacy formats, or formats outside
of the control of the project. I think if we start off with a format that
we can't change because of external reasons (whatever they may be), it will
be much harder to incrementally get to the right design. Does that seem
reasonable (and hopefully help explain the concrete suggestion I'm making)?
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