commit c0f6b37d1732e8e468899200caf3ec68886c7bfd
author Tess Strickland <sstrickl@google.com> Wed May 12 07:36:58 2021 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> Wed May 12 07:36:58 2021 +0000
tree 80e0d5be82e4db853a39a4a529662dc17923a531
parent 47e2acd1309d31923edeb100e877eab1fa7caf2a

[vm] Store compression info during GC visit macros.

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Adds a few type traits for operating on (Compressed)ObjectPtr types:

* is_compressed_ptr<T>::value is true for compressed pointer types and
  false for uncompressed pointer types.
* is_uncompressed_ptr<T>::value is false for compressed pointer types
  and true for uncompressed pointer types.
* base_ptr_type<T>::type is ObjectPtr for uncompressed pointer types and
  CompressedObjectPtr for compressed pointer types.

Note: If DART_COMPRESSED_POINTERS is not enabled, all pointers are
uncompressed and the above traits function accordingly. That means
that is_compressed_ptr<T>::value is always false,
is_uncompressed_ptr<T>::value is true for all object pointers, and
base_ptr_type<T>::type is ObjectPtr for all object pointers, even if
they contain Compressed in the name.

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The following changes have been made to the VISIT_* macros:

* VISIT_NOTHING: no change.
* VISIT_FROM: takes only a field name now, and retrieves the type of
  the field to determine which base pointer type to use for from().
  Note that VISIT_FROM must now come _after_ the declaration of the
  field, since it retrieves the type from the declaration.
* VISIT_TO: takes only a field name now, and retrieves the type of the
  field to determine which base pointer type to use for to().
* (removed) VISIT_TO_LENGTH: Instead, VISIT_TO creates a to() method
  that takes an optional length argument (defaults to 0).
* (new) VISIT_FROM_PAYLOAD_START: takes the object pointer type of the
  payload elements and creates a from() that returns the beginning
  element of the payload. Note that a payload element must be a single
  object ptr to use this macro.
* (new) VISIT_TO_PAYLOAD_END: takes the object pointer type of the
  payload elements and creates a to() which takes a non-optional length
  argument and returns the last element of the payload.  Note that a
  payload element must be a single object ptr to use this macro.

If one of the {COMPRESSED_,}VARIABLE_POINTER_FIELDS macros are used,
then VISIT_TO_PAYLOAD_END should not be, as those macros already
include a use of it.

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In addition, each Untagged<Class> class now has a static constexpr bool
field kContainsCompressedPointers. This field is false for
UntaggedObject, and for other Untagged<Class> classes, it is either
inherited from the parent class or set during VISIT_FROM and the new
VISIT_FROM_PAYLOAD_START macro.

VISIT_TO and the new VISIT_TO_PAYLOAD_END macro double-check at compile
time that the type retrieved or provided is a compressed type if
kContainsCompressedPointers is true, and uncompressed if false.

If the elements of a payload are not object pointers, but rather
a composite object that contains object pointers, then
VISIT_FROM_PAYLOAD_START/VISIT_TO_PAYLOAD_END cannot be used. Instead,
use DEFINE_COMPRESSED_POINTERS(type), where type is the type of one of
the object pointers in the composite object, to appropriately define
kContainsCompressedPointers.

Note that this field will always be false when DART_COMPRESSED_POINTERS
is not defined.

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For classes, a static constexpr ContainsCompressedPointers() predicate
is created, based on the associated untagged class's field.

For instances of Class, there is an instance predicate
Class::HasCompressedPointers() that returns whether instances of a given
class object contain compressed pointers.

Change all calls to InitializeObject and Object::Allocate to pass in
the result of the appropriate predicate.

TEST=Refactoring, so current tests on CI, especially on x64c trybots.

Cq-Include-Trybots: luci.dart.try:vm-kernel-linux-debug-x64c-try,vm-kernel-precomp-linux-debug-x64c-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-linux-debug-x64-try
Change-Id: Ifb61f72885bd8b951167becbccf8ec3337a922b1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/196931
Reviewed-by: Liam Appelbe <liama@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>