Unlike cfc8e6de, this does _not_ replace the default variable length
encoding for {Read,Write}Streams, but insteads adds separate
{Read,Write}{S,}LEB128 methods to the appropriate classes. If we later
find the cause of the issues that led to the revert of cfc8e6de, it'll
be easy to switch over then.
Note that WriteLEB128 asserts that the value is non-negative if used
with a signed type (since negative values suggests that SLEB128 should
be used instead for minimal encoding).
Also removes the various other encoding and decoding methods for
(S)LEB128 across the codebase and changes those clients to use
{Read,Write}Streams instead.
Other cleanups:
* Various constant-related cleanups in datastream.h.
* Adds DART_FORCE_INLINE to ReadStream::ReadByte and uses it in the
default variable length decoding methods for retrieving bytes
from the stream instead of managing current_ by hand.
* Creates a canonical empty CompressedStackMaps instance and uses
that instead of the null CompressedStackMaps instance in most cases.
The only remaining (expected) use of the null CompressedStackMaps
instance is for the global table in the object store when no global
table exists (e.g., in JIT mode before any snapshotting).
* Moves CompressedStackMapsIterator from code_descriptors.h to an
Iterator class within CompressedStackMaps in object.h (similar to
PcDescriptors::Iterator), to limit friend declarations and because it
conceptually makes more sense as part of CompressedStackMaps.
* Removed CompressedStackMaps::PayloadByte, since existing clients
(CompressedStackMaps::Iterator, StackMapEntry in program_visitor.cc)
are better served by just operating on the payload buffer directly
(with appropriate NoSafepointScopes).
* WriteStreams no longer allocate their initial space on construction,
but rather on the first write, so no allocation is performed by
constructing a never-used WriteStream.
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-debug-simarm_x64-try,vm-kernel-precomp-mac-release-simarm64-try,vm-kernel-mac-debug-x64-try,vm-kernel-win-debug-x64-try,vm-kernel-win-debug-ia32-try,vm-kernel-precomp-win-release-x64-try,vm-kernel-ubsan-linux-release-x64-try,vm-kernel-tsan-linux-release-x64-try,vm-kernel-precomp-ubsan-linux-release-x64-try,vm-kernel-precomp-tsan-linux-release-x64-try,vm-kernel-precomp-msan-linux-release-x64-try,vm-kernel-precomp-asan-linux-release-x64-try,vm-kernel-msan-linux-release-x64-try,vm-kernel-asan-linux-release-x64-try
Change-Id: Ice63321abaa79157fbe9f230a864c8bba0e6dea9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/166421
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>
Tess Strickland
45a46ca2b8