Once Reduction Pass improvement

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#4,124 opened on Sep 5, 2021 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 4/5
Estimated time: 3-5 days
Newbie friendliness: 35/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Stale
Tech stack: cpp, wasm
Domain: compilers

Research direction

Start with the linked PR #4111 and locate the Once Reduction pass implementation, then compare its handling of the two CFG shapes shown in the issue. Add a regression test for the second example and verify that the optimization no longer produces unsound behavior.

Written by the indexing model from the issue text.

Description

Recent Once Reduction pass properly handled following CFG in pseudocode:

bool initialized = false;
void boo() {
  if (initialized) return;
  ...
  initialized = true;
}

but unsound for this:

bool initialized = false;
void boo() {
  if (!initialized) {
    ...
    initialized = true;
  }
}

Dominant language: WebAssembly
Stars: 8.6k
Forks: 885
Avg merge: 2d 1h
Merged PRs (30d): 70

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