[External] : Re: RFC - Improving C2 Escape Analysis

[John Rose]

That sounds like an excellent approach:  Get some
wins and build some infrastructure before Valhalla,
but with an eye towards improving Valhalla also.

I was in a conversation just this morning where
stack allocation came up, as a possible way to handle
some instances of identity-free Valhalla objects.
The point would be to allow access consistent
with the layout of a heap object, but with allocation
on the stack.  The tactics we use today are either
full scalarization (preferable usually) or heap
buffering (like an old-school boxed primitive).
Stack allocation might be a useful intermediate
tactic.  (Maybe also consider thread-local heaps,
with explicit deallocation or just their own GC.)
Those extra thread-local or stack/activation-local
tactics are expensive and may not pay off in the
long run, but you are doing the right thing in
investigating them.  If and when you find wins
for regular pre-Valhalla objects, you are also
finding wins (probably) for Valhalla objects.

Anyway, thanks for looking at this stuff.  It’s
a pleasure to collaborate.


On Oct 12, 2021, at 10:48 AM, Cesar Soares Lucas <Divino.Cesar at microsoft.com<mailto:Divino.Cesar at microsoft.com>> wrote:

Hi, again, John.

First of all, we greatly appreciated the feedback that you provided to us.
Thank you.

I talked with my manager and the team and it's clear to us that contributing
to Valhalla is the best long-term strategy. Therefore, we'll be looking into
how to contribute to it in the near future.

That being said, we believe that improving the current EA and dependent
optimizations seems to be the best short-term strategy for us and for that
reason we'll invest our immediate efforts in that direction. We also believe
that this approach will help us gain more experience with the problem and
the platform overall.