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JIT: clear BBF_DONT_REMOVE on the new preheader in loop inversion - #136043
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lewing merged 3 commits intoOct 19, 2026
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…sm control flow Loop inversion splits a catch handler entry with fgSplitBlockAtEnd; the new preheader inherits BBF_DONT_REMOVE. If the loop later becomes unreachable, fgRemoveBlocksOutsideDfsTree keeps that block as an empty throw, and Wasm control flow (which lays out only DFS blocks) asserts that block order disagrees with preorder numbers. Before removing unreachable blocks for Wasm, clear BBF_DONT_REMOVE on unreachable blocks that are not EH region entries or call-finally pairs. Fixes dotnet#136041 Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1324801d-f940-4cf8-83cc-634c4510d91f
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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1324801d-f940-4cf8-83cc-634c4510d91f
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Replace the Wasm-only unreachable block cleanup with a fix at the source. Loop inversion splits the preheader with fgSplitBlockAtEnd, and the new preheader inherits BBF_DONT_REMOVE. When the old preheader is a handler entry and the loop later becomes unreachable, the new block can't be removed. Other targets emit it as a dead throw; Wasm control flow asserts. The old preheader keeps its EH entry role, so the new block doesn't need the flag. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1324801d-f940-4cf8-83cc-634c4510d91f
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October 19, 2026 01:52
EgorBo
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Oct 19, 2026
lewing
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October 19, 2026 22:42
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/ba-g failure looks like a very rare reoccurrence of #116753 not worth reopening unless it recurs more than once every 6+ months |
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Loop inversion splits the preheader with
fgSplitBlockAtEnd, and the new preheader inheritsBBF_DONT_REMOVE. When the old preheader is a catch handler entry and the loop condition later folds to false, the new block becomes unreachable but can't be removed. On Wasm its stalebbPreorderNumtripsblock order disagrees with preorder numinfgWasmControlFlow; other targets emit a deadint3/brk.The old preheader stays the EH entry, so this clears the flag on the new block, as the OSR entry code in
fgopt.cppdoes.fgSplitBlockAtEnditself must keep copying the flag, because loop canonicalization relies on it when splitting try entries.Resolves #136041
SuperPMI: diffs (dead throw removals only)
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This PR description was drafted with GitHub Copilot.