commit eb8865408468fac1bbe002e8eefad187719f4c7a
author Vyacheslav Egorov <vegorov@google.com> Thu Jun 27 21:58:57 2024 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Jun 27 21:58:57 2024 +0000
tree 163534f1ac96315948dd3a614efefa2d7a942e30
parent b13bd5b89169524a85477a807540869585b8f2fc

[vm] Avoid `GetBlock` in EliminateEnvironments and DelayAllocations

GetBlock has linear time complexity, so calling repetetively
might lead to quadratic complexity in pathological cases.

This avoids `GetBlock` in two places in the compiler:

- In EliminateEnvironments we were asking `current->GetBlock()`
  while iterating instructions inside a known `block`. This
  can obviously be short-circuited to just use that `block` directly.
- DelayAllocations we were calling `def->GetBlock()` and
  `use->GetBlock()`
  - `def->GetBlock()` is known because `def` is an instruction
    inside the block which were currently iterating, which means we
    can just use that block directly;
  - `use->GetBlock()` can be computed by `DominantUse(...)` which
    computes the `use` by iterating backwards from each use: during
    this iteration we will either hit
      a. a block entry - thus computing `use->GetBlock()`;
      b. `def` - thus establishing that `use` is in the same
         block as `def`; or
      c. another use - which means this is not dominant use.

R=alexmarkov@google.com

Fixes https://github.com/flutter/flutter/issues/150182

TEST=ci

Cq-Include-Trybots: luci.dart.try:vm-aot-linux-debug-x64-try,vm-aot-dwarf-linux-product-x64-try,vm-aot-linux-release-arm64-try
Change-Id: If7dcd74c01236d3bca9499883b51d273764e739c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/373502
Commit-Queue: Slava Egorov <vegorov@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>