[csa] verify skipped write-barriers in MemoryOptimizer

With very few exceptions, this verifies all skipped write-barriers in
CSA and Torque, showing that the MemoryOptimizer together with some
type information on the stored value are enough to avoid unsafe skipped

Changes to CSA:
SKIP_WRITE_BARRIER and Store*NoWriteBarrier are verified by the
MemoryOptimizer by default.
Type information about the stored values (TNode<Smi>) is exploited to
safely skip write barriers for stored Smi values.
In some cases, the code is re-structured to make it easier to consume
for the MemoryOptimizer (manual branch and load elimination).

Changes to the MemoryOptimizer:
Improve the MemoryOptimizer to remove write barriers:
- When the store happens to a CSA-generated InnerAllocate, by ignoring
  Bitcasts and additions.
- When the stored value is the HeapConstant of an immortal immovable root.
- When the stored value is a SmiConstant (recognized by BitcastToTaggedSigned).
- Fast C-calls are treated as non-allocating.
- Runtime calls can be white-listed as non-allocating.

Remaining missing cases:
- C++-style iterator loops with inner pointers.
- Inner allocates that are reloaded from a field where they were just stored
  (for example an elements backing store). Load elimination would fix that.
- Safe stored value types that cannot be expressed in CSA (e.g., Smi|Hole).
  We could handle that in Torque.
- Double-aligned allocations, which are not lowered in the MemoryOptimizer
  but in CSA.

Drive-by change: Avoid Smi suffix for StoreFixedArrayElement since this
can be handled by overload resolution (in Torque and C++).


Change-Id: I0af9b710673f350e0fe81c2e59f37da93c024b7c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1571414
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61016}
24 files changed
tree: 6c84ac9aec6a4cd77fe8cc1ca024c785ca863abc
  1. .clang-format
  2. .clang-tidy
  3. .editorconfig
  4. .git-blame-ignore-revs
  5. .gitattributes
  6. .gitignore
  7. .gn
  8. .vpython
  9. .ycm_extra_conf.py
  11. BUILD.gn
  13. ChangeLog
  14. DEPS
  16. LICENSE.fdlibm
  17. LICENSE.strongtalk
  18. LICENSE.v8
  19. LICENSE.valgrind
  20. OWNERS
  21. PRESUBMIT.py
  22. README.md
  24. benchmarks/
  25. build_overrides/
  26. codereview.settings
  27. custom_deps/
  28. docs/
  29. gni/
  30. include/
  31. infra/
  32. samples/
  33. snapshot_toolchain.gni
  34. src/
  35. test/
  36. testing/
  37. third_party/
  38. tools/

V8 JavaScript Engine

V8 is Google's open source JavaScript engine.

V8 implements ECMAScript as specified in ECMA-262.

V8 is written in C++ and is used in Google Chrome, the open source browser from Google.

V8 can run standalone, or can be embedded into any C++ application.

V8 Project page: https://v8.dev/docs

Getting the Code

Checkout depot tools, and run

    fetch v8

This will checkout V8 into the directory v8 and fetch all of its dependencies. To stay up to date, run

    git pull origin
    gclient sync

For fetching all branches, add the following into your remote configuration in .git/config:

    fetch = +refs/branch-heads/*:refs/remotes/branch-heads/*
    fetch = +refs/tags/*:refs/tags/*


Please follow the instructions mentioned at v8.dev/docs/contribute.