tree 305ab06cf4f36aa8f7e399c3d5951cad17e4784e
parent 32f6f94ab580945245b21c4d534cdc15f4f55499
author Daco Harkes <dacoharkes@google.com> 1630909739 +0000
committer Daco Harkes <dacoharkes@google.com> 1630909739 +0000

[vm] Introduce immutable maps and sets in backend

This CL introduces immutable maps and sets in the VM backend but does
not yet target them from the frontend. The changes are tested by unit
tests constructing these immutable maps and sets.

This CL introduces immutable variants of the hash map and set in
compact_hash.dart and recognizes them in the VM. The immutable ones
use a different mixin with a different recognized method for accessing
members.
* Data list is an immutable list with a different cid. (Otherwise the
  optimizer notices that immutable and mutable lists cannot be equal.)
* Index is a nullable mutable typed data. (Otherwise optimizer removes
  necessary null checks.)
* Index should use a store-release barrier when written to.

Multiple isolates might lazily compute the index for const sets and
maps. This is fine because all identityHashCodes and hashCodes are
guaranteed to be race-free. The later isolates will override the index
pointer with an identical index.

This CL does not introduce support for using these immutable maps and
sets in AOT (clustered_snapshot) and in messages to other isolates
(message_snapshot) because that is harder to test with unit tests. That
will be added in the follow-up CL.

Design doc: go/dart-vm-const-maps

TEST=runtime/vm/object_test.cc

Bug: https://github.com/dart-lang/sdk/issues/45908

Change-Id: I4042179c15e8b37692d3255655351c01c7124991
Cq-Include-Trybots: luci.dart.try:analyzer-nnbd-linux-release-try,app-kernel-linux-debug-x64-try,dart-sdk-linux-try,front-end-nnbd-linux-release-x64-try,pkg-linux-debug-try,vm-canary-linux-debug-try,vm-kernel-asan-linux-release-x64-try,vm-kernel-checked-linux-release-x64-try,vm-kernel-linux-debug-x64c-try,vm-kernel-linux-debug-x64-try,vm-kernel-linux-debug-simarm64c-try,vm-kernel-nnbd-linux-release-simarm-try,vm-kernel-optcounter-threshold-linux-release-x64-try,vm-kernel-precomp-android-release-arm_x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-debug-x64c-try,vm-kernel-reload-linux-debug-x64-try,vm-kernel-reload-rollback-linux-debug-x64-try,vm-precomp-ffi-qemu-linux-release-arm-try,vm-kernel-precomp-linux-debug-simarm_x64-try,vm-kernel-precomp-linux-debug-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/210860
Reviewed-by: Martin Kustermann <kustermann@google.com>