This reduces e mail module by -4% in compressed form. It does have
a increase of 2.5% in uncompressed form. This is due to repeated
entries in the element section of the dynamic dispatch table and
will be addressed in future CLs.
Currently if the main module of an app has a dynamic call, it will have
a caller-shape specific dynamic dispatcher that checks (via class ids)
all possible targets in the app and issues calls to them.
That means the code size is O(targets) - even if most targets reside in
deferred modules.
We change this now to use a row displacement table based dispatch,
just as our normal typed dispatch table. Though there's a few
differences
* In a typed call we know the target exists, in a dynamic call we don't
know whether the target exists (it may be a NSM case). To accomodate
for this we make 2 wasm tables of the same layout: First we load a
table of i31refs and check if the value is in agreement with the
receiver class id. If so we have a match and can load the actual
destination from the funcref table.
* In typed calls we use one row in the table for each selector. In the
dynamic invocation case we'll use one row per dynamic selector + call
shape.
* The wasm module that contains the actual instance method will also
hold all it's dynamic forwarder functions (one per dynamic caller
shape). The elements section of that module will cause initialization
of the two slots in the two tables mentioned above.
Issue https://github.com/dart-lang/sdk/issues/62639
Change-Id: I4e631f98fe9c58e2110bac34c3f5ff6d11bef909
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/487660
Reviewed-by: Srujan Gaddam <srujzs@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
Martin Kustermann
b1df65ded8