Resolve inconsistent treatment of stubs in kAppJIT snapshots in favor of write stubs in the snapsho…

Resolve inconsistent treatment of stubs in kAppJIT snapshots in favor of writing stubs in the snapshot.

Remember Instructions offsets using the object id weak table. Fixes duplication of instruction objects in non-product kAppJIT snapshots. Also provides a good basis for referencing VM isolate Instructions from an isolate snapshot.

R=asiva@google.com

Committed: https://github.com/dart-lang/sdk/commit/e3a07d314590c6099d8fa8458a74d2f253561a21

[rmacnak, 2017-05-03 19:53:52]

rmacnak@google.com changed reviewers:
+ asiva@google.com

[rmacnak, 2017-05-03 19:53:53]

https://codereview.chromium.org/2859913002/diff/1/runtime/vm/clustered_snapsh...
File runtime/vm/clustered_snapshot.cc (right):

https://codereview.chromium.org/2859913002/diff/1/runtime/vm/clustered_snapsh...
runtime/vm/clustered_snapshot.cc:4876: if (Snapshot::IncludesCode(kind_)) {
Not adding the stubs as base objects for kAppJIT makes things consistent with
writing the stubs here, and with Dart::InitOnce not creating the stubs if
running from kAppJIT.

Currently the VM isolate snapshot is never kAppJIT, which is why this has gone
unnoticed, but it may be useful to for the VM isolate snapshot to include common
instructions on Fuchsia.

https://codereview.chromium.org/2859913002/diff/1/runtime/vm/snapshot.cc
File runtime/vm/snapshot.cc (left):

https://codereview.chromium.org/2859913002/diff/1/runtime/vm/snapshot.cc#oldc...
runtime/vm/snapshot.cc:691: // Instructions are only dedup in product mode
because it obfuscates profiler
This comment is misleading. To effectively deduplicate instructions, we need to
both

1) Update Code objects to point to canonical Instruction objects
2) Use the same text offset if we encounter the same Instruction object multiple
times

1 is achieved by ProgramVisitor::DedupInstructions() and that only runs in
PRODUCT mode.
2 was achieved by this code but is now achieved by the use of the object id
table.

[siva, 2017-05-09 01:41:49]

lgtm

[rmacnak, 2017-05-09 16:53:34]

Description was changed from

==========
Resolve inconsistent treatment of stubs in kAppJIT snapshots in favor of write
stubs in the snapshot.

Remember Instructions offsets using the object id weak table. Fixes duplication
of instruction objects in non-product kAppJIT snapshots. Also provides a good
basis for references VM isolate Instructions from an isolate snapshot.
==========

to

==========
Resolve inconsistent treatment of stubs in kAppJIT snapshots in favor of writing
stubs in the snapshot.

Remember Instructions offsets using the object id weak table. Fixes duplication
of instruction objects in non-product kAppJIT snapshots. Also provides a good
basis for referencing VM isolate Instructions from an isolate snapshot.
==========

[rmacnak, 2017-05-09 17:04:28]

Description was changed from

==========
Resolve inconsistent treatment of stubs in kAppJIT snapshots in favor of writing
stubs in the snapshot.

Remember Instructions offsets using the object id weak table. Fixes duplication
of instruction objects in non-product kAppJIT snapshots. Also provides a good
basis for referencing VM isolate Instructions from an isolate snapshot.
==========

to

==========
Resolve inconsistent treatment of stubs in kAppJIT snapshots in favor of writing
stubs in the snapshot.

Remember Instructions offsets using the object id weak table. Fixes duplication
of instruction objects in non-product kAppJIT snapshots. Also provides a good
basis for referencing VM isolate Instructions from an isolate snapshot.

R=asiva@google.com

Committed:
https://github.com/dart-lang/sdk/commit/e3a07d314590c6099d8fa8458a74d2f253561a21
==========

[rmacnak, 2017-05-09 17:04:30]

Committed patchset #1 (id:1) manually as
e3a07d314590c6099d8fa8458a74d2f253561a21 (presubmit successful).