Previously, the VM used a linear array to cache previous instantiations
of a type arguments object. Now once the cache hits a certain number
of occupied entries, the VM changes to using a hash-based approach.
The InstantiateTypeArguments stubs have not yet been updated to
traverse the hash-based cache, so once the cache has grown too large,
all attempts at instantiations, even those that are in the cache, go to
the runtime. Thus, until the stubs are updated, this is only an
improvement if the cost of traversing the linear cache dominates the
cost of making a runtime call. Our benchmarks see a ~40% performance
regression for hash-based caches of size 100 but a ~400% performance
improvement for hash-based caches of size 1000. Thus, we currently
split the difference and set the maximum size of linear caches to 500.
TEST=vm/cc/TypeArguments_Cache_ManyInstantiations
Bug: https://github.com/dart-lang/sdk/issues/48344
Change-Id: I7f1376943523bb5bcd8b175cfb1936779ea73d60
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-dwarf-linux-product-x64-try,vm-kernel-precomp-linux-product-x64-try,vm-kernel-precomp-linux-release-x64-try,vm-kernel-precomp-nnbd-mac-release-arm64-try,vm-kernel-precomp-nnbd-linux-release-simarm_x64-try,vm-kernel-precomp-linux-release-simarm-try,vm-kernel-precomp-nnbd-linux-release-x64-try,vm-kernel-precomp-nnbd-linux-release-simarm64-try,vm-kernel-precomp-nnbd-linux-debug-simriscv64-try,vm-kernel-precomp-tsan-linux-release-x64-try,vm-kernel-tsan-linux-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/265325
Reviewed-by: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>
Tess Strickland
4f925105cf