[vm/compiler] Avoid adding unused Redefinition instructions

Type propagator adds Redefinition instructions to provide more accurate
type information only for dominated uses (for example, to mark receiver
as non-nullable after instance calls). However, adding Redefinition
instructions may interfere with branch simplification, which looks only
at empty join blocks. This change avoids adding unused Redefinition
instructions (if there are no dominated uses).

This particular situation happens in Flutter in RenderObject.layout() where
constraints.isTight is inlined with multiple polymorphic targets, including
SliverConstraints.isTight which returns false.
Branch simplification was not happening due to Redefinition instruction
for 'constraints'. That Redefinition instruction is not used.

Change-Id: I15082bacd7cc6ea1445a4dadc8ef97853142ba74
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/103023
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
1 file changed
tree: 65373da50fef156fbe231301281b84f09ef15a1e
  1. .github/
  2. build/
  3. client/
  4. docs/
  5. pkg/
  6. runtime/
  7. samples/
  8. samples-dev/
  9. sdk/
  10. tests/
  11. third_party/
  12. tools/
  13. utils/
  14. .clang-format
  15. .gitattributes
  16. .gitconfig
  17. .gitignore
  18. .gn
  19. .mailmap
  20. .packages
  21. .vpython
  22. AUTHORS
  23. BUILD.gn
  24. CHANGELOG.md
  25. codereview.settings
  26. CONTRIBUTING.md
  27. DEPS
  28. LICENSE
  29. PATENTS
  30. PRESUBMIT.py
  31. README.dart-sdk
  32. README.md
  33. WATCHLISTS
README.md

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