[PATCH] D28964: [PGO] Value profile support for value ranges

[Rong Xu via llvm-commits]

On Mon, Jan 23, 2017 at 10:22 AM, David Li via Phabricator <
reviews at reviews.llvm.org> wrote:

> davidxl added a comment.
>
> A general comment.
>
> The range profiling should not be limited to just memory intrinsics.  It
> should be designed to be a more general interval profiler. Interval
> profiler is also useful for other value profiling transformations such as
> mod operation for integer values (x%y). The value profiler can do interval
> profiling for division x/y and track resulting values in interval [0, 1].
>

why do we need to track the result? I think usually we profile the divisor.
Current code can track the range of divisor. The only issue is that I
assume the type to be unsigned.


> In a more general form, an interval profiler API should specify the
> following things
>
> 1. counter index
> 2. interval start and end (inclusive) : [S, E]
> 3. optionally specify the start value of a large value range [SL, inf)
>
> 3 + (E-S+1)  values will be tracked:
> (-inf, S) one value
> [S,E] one for each in the range
> [E, SL) one value
> [SL, inf) for one.
>
> The client (instrumentor) decides the the interval boundaries depending on
> the value profile kind.
>
>
Index is obtained incrementally in the instrumentation. I don't think it's
necessary to expose it to the API.
right now, there is options to control the intervals. it's universal to all
range profiles.
I can have the client choose the intervals by including it into the
instrumentation intrinsic.



>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D28964
>
>
>
>
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