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RemoveUnusedBrs: optimize unreachable control flow mixed with side-effecting branches #7639

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Merged
merged 27 commits into from
Jun 24, 2025
Merged

RemoveUnusedBrs: optimize unreachable control flow mixed with side-effecting branches #7639

merged 27 commits into from
Jun 24, 2025

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xuruiyang2002
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Currently wasm-opt cannot optimize unused branch complexed with side-effect operations, such as

 (func $_start
  (local $0 i32)
  (block $block
   (br_if $block
    (local.tee $0
     (i32.const 1)
    )
   )
   (br_if $block
    (i32.load
     (i32.const 0)
    )
   )
   (local.set $0
    (i32.const 0)
   )
  )
  (i32.store
   (i32.const 0)
   (local.get $0)
  )
 )

Actually, the whole block can be removed. However, O3 cannot optimize it (while O2 could).

Fixes: #7637

kripken
kripken reviewed Jun 4, 2025
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xuruiyang2002
xuruiyang2002 commented Jun 5, 2025
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xuruiyang2002
xuruiyang2002 commented Jun 5, 2025
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kripken
kripken reviewed Jun 11, 2025
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kripken
kripken reviewed Jun 12, 2025
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@xuruiyang2002
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BTW: fuzzing for about one hour, and no bad news.

kripken
kripken reviewed Jun 16, 2025
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kripken
kripken reviewed Jun 17, 2025
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kripken
kripken reviewed Jun 20, 2025
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kripken
kripken reviewed Jun 20, 2025
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@kripken kripken merged commit 9bd8871 into WebAssembly:main Jun 24, 2025
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@xuruiyang2002 xuruiyang2002 deleted the opt_br_if_cond branch June 25, 2025 04:57
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@kripken kripken kripken approved these changes

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Successfully merging this pull request may close these issues.

Significant optimization regression due to failing remove unused branch
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@xuruiyang2002 @kripken