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Drop Code objects in AOT (PRODUCT && dwarf_stack_traces) #44852

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3 tasks done
alexmarkov opened this issue Feb 3, 2021 · 1 comment
Closed
3 tasks done

Drop Code objects in AOT (PRODUCT && dwarf_stack_traces) #44852

alexmarkov opened this issue Feb 3, 2021 · 1 comment
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area-vm Use area-vm for VM related issues, including code coverage, FFI, and the AOT and JIT backends. vm-aot-code-size Related to improvements in AOT code size vm-aot-memory-footprint Related to improvements of VM memory footprint for AOT deployments
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Dart VM memory footprint

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@alexmarkov
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alexmarkov commented Feb 3, 2021 •
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In AOT mode, when vm_service/profiler is not present (PRODUCT/flutter-release build) and --dwarf-stack-traces is used, there is a little need for Code objects. Currently, Code objects occupy significant portion of heap size of objects in the snapshot, so removing them would decrease memory usage and would also reduce AOT snapshot size.

In order to remove most Code objects we need:

  • Provide an alternative lookup mechanism to access CompressedStackMaps corresponding to a given PC.
  • Remove uses of Code from stack traces in --dwarf-stack-traces mode.
  • Remove most uses of ReversePc::Lookup.

For now, we can keep Code objects for exception handling as there is only a small number of codes with exception handlers.
@alexmarkov alexmarkov added area-vm Use area-vm for VM related issues, including code coverage, FFI, and the AOT and JIT backends. vm-aot-code-size Related to improvements in AOT code size vm-aot-memory-footprint Related to improvements of VM memory footprint for AOT deployments labels Feb 3, 2021
@alexmarkov alexmarkov self-assigned this Feb 3, 2021
@a-siva a-siva added this to Tasks in Dart VM memory footprint via automation Feb 3, 2021
dart-bot pushed a commit that referenced this issue Feb 4, 2021
@alexmarkov
[vm/aot] Remove reverse PC lookup from switchable calls
d423a3c 
This is a preparation for removal of Code objects.

Issue: #44852
TEST=ci
Change-Id: I9765945731c91fbdac647cc448d021238f129880
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/182361
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
dart-bot pushed a commit that referenced this issue Feb 17, 2021
@alexmarkov
[vm/aot] Avoid using most Code objects in stack traces with --dwarf-s…
b6dc4da 
…tack-traces

The following changes are done in preparation for the removal of Code
objects in AOT with --dwarf-stack-traces:

* Stack trace objects are extended to hold uword PCs (which may not
  fit into Smi range).

* Scanning stack frames in GC (StackFrame::VisitObjectPointers)
  now avoids using Code objects.
  In order to find CompressedStackMaps it now calls
  ReversePc::FindCompressedStackMaps.

* Singleton Code object (StubCode::UnknownDartCode()) is prepared as
  a replacement for Code objects in stack traces. It has
  PayloadStart() == 0 and Size() == kUwordMax so it includes
  arbitrary PCs.

* In --dwarf-stack-traces mode, most Code objects obtained from stack
  frames are replaced with StubCode::UnknownDartCode().
  This simulates future behavior of ReversePc::Lookup when Code objects
  will be removed.

Issue: #44852
Change-Id: I7cec7b8b9396c9cfeca3c256a412ba4e82a7e0c4
TEST=ci
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/182720
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Tess Strickland <sstrickl@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
dart-bot pushed a commit that referenced this issue Feb 18, 2021
@alexmarkov
Revert "[vm/aot] Avoid using most Code objects in stack traces with -…
fde0ed2 
…-dwarf-stack-traces"

This reverts commit b6dc4da.

Reason for revert: broke package:vm_snapshot_analysis in Flutter
(flutter/flutter#76313).

Original change's description:
> [vm/aot] Avoid using most Code objects in stack traces with --dwarf-stack-traces
>
> The following changes are done in preparation for the removal of Code
> objects in AOT with --dwarf-stack-traces:
>
> * Stack trace objects are extended to hold uword PCs (which may not
>   fit into Smi range).
>
> * Scanning stack frames in GC (StackFrame::VisitObjectPointers)
>   now avoids using Code objects.
>   In order to find CompressedStackMaps it now calls
>   ReversePc::FindCompressedStackMaps.
>
> * Singleton Code object (StubCode::UnknownDartCode()) is prepared as
>   a replacement for Code objects in stack traces. It has
>   PayloadStart() == 0 and Size() == kUwordMax so it includes
>   arbitrary PCs.
>
> * In --dwarf-stack-traces mode, most Code objects obtained from stack
>   frames are replaced with StubCode::UnknownDartCode().
>   This simulates future behavior of ReversePc::Lookup when Code objects
>   will be removed.
>
> Issue: #44852
> Change-Id: I7cec7b8b9396c9cfeca3c256a412ba4e82a7e0c4
> TEST=ci
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/182720
> Commit-Queue: Alexander Markov <alexmarkov@google.com>
> Reviewed-by: Tess Strickland <sstrickl@google.com>
> Reviewed-by: Martin Kustermann <kustermann@google.com>

Issue: #44852
Change-Id: I6f66171eecf1133363a7ce56193e782e43a20baf
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/185488
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
dart-bot pushed a commit that referenced this issue Feb 22, 2021
@alexmarkov
Reland "[vm/aot] Avoid using most Code objects in stack traces with -…
ddfc983 
…-dwarf-stack-traces"

This is a reland of b6dc4da

TEST=ci

Original change's description:
> [vm/aot] Avoid using most Code objects in stack traces with --dwarf-stack-traces
>
> The following changes are done in preparation for the removal of Code
> objects in AOT with --dwarf-stack-traces:
>
> * Stack trace objects are extended to hold uword PCs (which may not
>   fit into Smi range).
>
> * Scanning stack frames in GC (StackFrame::VisitObjectPointers)
>   now avoids using Code objects.
>   In order to find CompressedStackMaps it now calls
>   ReversePc::FindCompressedStackMaps.
>
> * Singleton Code object (StubCode::UnknownDartCode()) is prepared as
>   a replacement for Code objects in stack traces. It has
>   PayloadStart() == 0 and Size() == kUwordMax so it includes
>   arbitrary PCs.
>
> * In --dwarf-stack-traces mode, most Code objects obtained from stack
>   frames are replaced with StubCode::UnknownDartCode().
>   This simulates future behavior of ReversePc::Lookup when Code objects
>   will be removed.
>
> Issue: #44852
> Change-Id: I7cec7b8b9396c9cfeca3c256a412ba4e82a7e0c4
> TEST=ci
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/182720
> Commit-Queue: Alexander Markov <alexmarkov@google.com>
> Reviewed-by: Tess Strickland <sstrickl@google.com>
> Reviewed-by: Martin Kustermann <kustermann@google.com>

Change-Id: Ia2fc4672a085cd963b7fc103369851df3603590c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/186202
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
Reviewed-by: Tess Strickland <sstrickl@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
dart-bot pushed a commit that referenced this issue Feb 27, 2021
@alexmarkov
[vm/aot] Partially remove Code objects from AOT snapshots
26e7106 
Code objects which do not carry useful information are
marked as 'discarded' during precompilation. Snapshot
serializer only writes instructions, compressed stack
maps and state bits for discarded Code objects.

This is a preliminary step before deserializer would be able
to omit creating instances for discarded Code objects at
runtime.

On a large app, AOT-compiled in PRODUCT mode with
--dwarf-stack-traces on arm64:
Discarded: 77% of all Code objects in snapshot.
Uncompressed AOT snapshot size -1.9%.

AOT snapshot size of Flutter gallery in release-sizeopt mode:
arm64 uncompressed -2.1% (gzip -0.6%, brotli -0.7%)
arm32 uncompressed -1.9% (gzip -0.6%, brotli -0.7%)

TEST=ci
Issue: #44852

Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-product-x64-try,vm-kernel-precomp-linux-release-x64-try,vm-kernel-precomp-linux-debug-x64-try,pkg-mac-release-try
Change-Id: I159cfebbdac76cc60060fedb1d22ed86672a68a1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/187600
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
dart-bot pushed a commit that referenced this issue Mar 13, 2021
@alexmarkov
[vm/aot] Fix retaining of exception types and auxiliary functions
11d6203 
There are two fixes:

1) If a function was compiled but not retained, precompiler
should still trace through types used in exception handlers.

2) Certain auxiliary functions such as implicit closure functions
and field initializers were added to 'possibly_retained_functions_'
set but were not traced through AddTypesOf and were not added to
'functions_to_retain_' set.

Flutter gallery AOT snapshot size
release - no changes
release-sizeopt arm +0.13%, arm64 +0.14%

TEST=ci
Fixes #45179
Issue #44852

Change-Id: Ide9a7e82a7bb9098dc90bc41a76e527e7a5cb603
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/190781
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Tess Strickland <sstrickl@google.com>
dart-bot pushed a commit that referenced this issue Mar 15, 2021
@alexmarkov
[vm/aot] Remove special cases of dynamic function lookups from precom…
16beb34 
…piler

Flutter gallery AOT snapshot size
release: no change;
release-sizeopt: arm -0.24%, arm64 -0.25%.

TEST=ci
Issue: #44852
Change-Id: I847bfc311552bb4e80222e0040b50b4766a18dbe
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/190783
Reviewed-by: Tess Strickland <sstrickl@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
dart-bot pushed a commit that referenced this issue Mar 31, 2021
@alexmarkov
[vm/compiler] Null-aware EqualityCompare instruction
4bf6de7 
This change extends EqualityCompare IL instruction to handle case
when operands are nullable ints.

Unlike CheckedSmiComparison, EqualityCompare performs comparison
without making a dynamic call on a slow path. Dynamic call in
CheckedSmiComparison is a problem because it is not present in
the original program and not properly tracked in TFA and precompiler,
so precompiler is not able to drop Code objects (needed for
dynamic calls) reliably.

This change removes the remaining case when CheckedSmiComparison
instruction was used. The cleanup will follow in a separate CL.

TEST=ci
Issue: #32166
Issue: #44852
Change-Id: I8114a2616becf632462d4cb3bfc255691f24e1ef
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/193447
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
dart-bot pushed a commit that referenced this issue Mar 31, 2021
@alexmarkov
[vm/compiler] Cleanup CheckedSmi* instructions
2a14259 
This is a final cleanup of CheckedSmiOpInstr and
CheckedSmiComparisonInstr instructions.

Their uses were removed in the following changes:

  https://dart-review.googlesource.com/c/sdk/+/191761
  https://dart-review.googlesource.com/c/sdk/+/191760
  https://dart-review.googlesource.com/c/sdk/+/193447

TEST=ci
Issue: #44852
Change-Id: Ica52ab9e2fcabab1913228818642a27a8d842f92
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/193449
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
dart-bot pushed a commit that referenced this issue Apr 13, 2021
@alexmarkov
[vm/aot] Discard Code objects from the heap
5129cff 
While deserializing AOT snapshot, Code objects which do not contain
valuable information besides entry point and stack maps are discarded
and not allocated on the heap (they are replaced with
StubCode::UnknownDartCode()).

PC -> Code/CompressedStackMaps lookup is implemented using a separate
table (InstructionsTable).

Flutter gallery in release-sizeopt mode:
Heap size of snapshot objects: arm -26.89%, arm64 -27.68%

Large Flutter application in release mode with --dwarf-stack-traces:
Heap size of snapshot objects: -24.3%.
Discarded Code objects: 72.5% of all Code objects.

Issue: #44852.

TEST=existing tests; "--dwarf_stack_traces --no-retain_function_objects
--no-retain_code_objects" mode is enabled for a few tests.

Change-Id: I5fe3e283630c8e8f4442319d5dcae38d174dd0d8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/189560
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
dart-bot pushed a commit that referenced this issue Apr 26, 2021
@alexmarkov
[vm/aot] Discard Code objects of entry points
db8d71d 
Calls from C++ to Dart entry points are currently performed by
calling via Function::entry_point() in AOT mode
(with --use_bare_instructions). Such calls no longer use
Code objects, so Code objects can be discarded even if they
belong to a Function which is used as an entry point.

TEST=ci
Issue: #44852
Change-Id: Iaf9dd67392780ef4344fc518865ffbe30648762e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/196720
Reviewed-by: Tess Strickland <sstrickl@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
dart-bot pushed a commit that referenced this issue Apr 27, 2021
@alexmarkov
[vm/aot] Discard Code objects of invisible functions
a98500a 
Previously, Code objects of invisible functions were retained
in order to omit frames corresponding to such functions from stack
traces when stack trace is printed.

This change drops Code objects of invisible functions. That also
means that frames corresponding to such functions are no longer
skipped in binary DWARF stack traces.

In order to account for that, DW_AT_artificial attribute is added to
generated DWARF debug information to mark invisible functions.
Stack trace decoding now looks at this attribute and skips those
frames when symbolizing stack trace.

Flutter gallery in release-sizeopt mode:
Heap size of snapshot objects -4.2% (arm), -4.4% (arm64).

A large application in --dwarf_stack_traces mode:
Number of discarded Code objects increased from 72.4% to 83.7%
(out of all Code objects).
Heap size of Code objects -37.4%.
Heap size of all snapshot objects -5%.

TEST=tests/standalone/dwarf_stack_trace_invisible_functions_test.dart
Issue: #44852
Change-Id: Ib804852aba1e083670f1d9b9d66cbaab7dcdcff9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/196583
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Tess Strickland <sstrickl@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
@alexmarkov
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Currently, about 83% of Code objects are removed on a large application in --dwarf_stack_traces mode.
We can either stop at this point, or continue discarding the remaining Code objects.

Remaining Code objects which can be potentially discarded:

  • stubs: 9.3%.
  • dynamically called functions: 2%.

The rest of the Code objects have exception handlers / pc descriptors / native functions etc and are not feasible to discard.

Dart VM memory footprint automation moved this from Tasks to Done Oct 18, 2023
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