[vm, lib] Refine List copy loops

`growableList.toList()` was 10-50% faster than `List.of(growableList)`.
This change erases the performance difference.

The loops were slightly different. The faster version created
the _List backing store for the list rather than assigning to the

It is not clear if the speedup is from an easier type test (the _List is
'raw'), or from a less indirect assignment, or from a fixed length list
having an an easier-to-optimize bounds check, or whether a non-zero loop
trip count enables any hoisting.

This change uses the faster pattern in the _GrowableList._ofXXXList

I tried to simplify `toList` to delegate to one of the methods
with the faster loop, but it was 2-5% slower on ListCopy.toList.2,
presumably the extra call is significant for a short list. If there
was an annotation for aggressive inlining into `toList` perhaps that
would close the gap.

dart-aot-null armv8c, 0.5 noise and over

ListCopy.List.num.from.2            24.17% (1.6 noise)
ListCopy.List.of.2                  28.08% (1.7 noise)
ListCopy.spread.num.2               28.73% (2.1 noise)
ListCopy.List.num.from.100          54.49% (1.9 noise)
ListCopy.List.of.100                55.55% (1.9 noise)
ListCopy.spread.num.100             55.77% (2.0 noise)

Change-Id: I7b780835faf50b673fd4b1a08a8c4e2d350d7d5b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/224780
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Stephen Adams <sra@google.com>
2 files changed
tree: 79bbc4a0d4c4ed4534772015e7ae38a0f6c75ce3
  1. .dart_tool/
  2. .github/
  3. benchmarks/
  4. build/
  5. docs/
  6. pkg/
  7. runtime/
  8. samples/
  9. samples-dev/
  10. samples_2/
  11. sdk/
  12. tests/
  13. third_party/
  14. tools/
  15. utils/
  16. .clang-format
  17. .gitattributes
  18. .gitconfig
  19. .gitignore
  20. .gn
  21. .mailmap
  22. .packages
  23. .style.yapf
  24. .vpython
  26. BUILD.gn
  27. CHANGELOG.md
  28. codereview.settings
  30. DEPS
  33. PRESUBMIT.py
  34. README.dart-sdk
  35. README.md
  36. sdk_args.gni
  37. SECURITY.md


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