Re: Creating a wrapper around a function at compile time

[Erick Ochoa <eochoa@gcc.gnu.org>]

On Thu, 14 Jul 2022 at 15:51, Richard Biener <richard.guenther@gmail.com>
wrote:

> With a value-profile it would be per call site and IPA-CP can use that
> to direct the cloning.  I'm not sure how many
> values a value histogram can track reliably here.
>

Last time I checked, value profiling can only track a single value per
statement. So that would need to be augmented if we wanted to specialize
for more than one parameter. However, this can also be a bad idea. Because
even if parameters a and b are quasi-constants, perhaps the cross product a
x b follows a more uniform distribution. This means that optimizing on a or
on b might be a good idea but optimizing on a x b is a bad idea. (There is
still some work to be done defining when specializing is a good idea or
not). Also, I do not believe that value profiling profiles arguments?
According to the comments only values regarding division and/or
indirect/virtual call specialization are tracked during value profiling.

However, even if value profiling would be a great addition to this, I would
like to explore the transformation independent of value profiling. There
are some heuristics that could be used, for example looking at the
callsites which do have constant arguments and which optimizations are
enabled by those constants.

You mention that: "IPA-CP can use that to direct the cloning". Can you
elaborate a bit further? I guess the idea here is augmenting ipa-cp with a
list of "likely values" and extend the infrastructure which deals with
speculation to support arguments. Am I following correctly? Any other
suggestions?