This change bakes binary search table which maps PC ranges
to corresponding stack maps and Code objects (if still present
in the snapshot) into RO data section of the snapshot - instead
of constructing it at load time.
This allows to considerably reduce amount of work done when
loading Code cluster for programs which have majority of their
Code objects discarded (i.e. in DWARF stack traces mode): as
we no longer write / read any information for discarded Code
objects.
This CL also changes program visitor to deduplicate Code objects
if their instructions are deduplicated in AOT mode. Only a single
Code object can be choose as a representative for the given
PC range so it does not make sense to write multiple Code objects
into the snapshot which refer to the same Instructions.
The overall improvement is hard to quantify but ReadProgramSnapshot
shows the following improvement when starting a large
Flutter application on a slow Android device:
before 223.55±59.94 (192.02 .. 391.74) ms
after 178.06±47.03 (151.31 .. 291.34) ms
This CL packs CompressedStackMaps next to the binary search table
itself allowing us to address them via offsets instead of
pointers.
Snapshot sizes are actually affected positively by this change. On
the same large Flutter application I see
DWARF stack traces on: -1.34% total SO size
DWARF stack traces off: -1.63% total SO size
Issue https://github.com/dart-lang/sdk/issues/46116
TEST=ci
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-dwarf-linux-product-x64-try,vm-kernel-precomp-linux-debug-simarm64c-try,vm-kernel-precomp-linux-debug-simarm_x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-debug-x64c-try,vm-kernel-precomp-linux-product-x64-try,vm-kernel-precomp-linux-release-simarm-try,vm-kernel-precomp-linux-release-simarm64-try,vm-kernel-precomp-linux-release-simarm_x64-try,vm-kernel-precomp-linux-release-x64-try
Change-Id: Ic997045a33daa81ec68df462a0792915885df66b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/220766
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Slava Egorov <vegorov@google.com>
Vyacheslav Egorov
13d27d669d