Fix IRList::structural_equals to ignore MFLOW_FALLTHROUGH - #997
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Fix IRList::structural_equals to ignore MFLOW_FALLTHROUGH#997rootkiller6788 wants to merge 2 commits into
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structural_equals compared every entry in the IR lists, including MFLOW_FALLTHROUGH no-ops. Two methods that differ only by a no-op placement (e.g. one has an unreferenced label lowered to FALLTHROUGH) were reported as not structurally equal. Trailing metadata/no-op entries after the last real instruction also caused a mismatch when the other list had already been fully consumed. Skip metadata and FALLTHROUGH entries on both sides before each comparison step, and skip any remaining trailing no-ops after the main loop. Add unit tests covering leading and trailing FALLTHROUGH entries. Closes facebook#778
structural_equals is a const method, so m_list.begin() and other.begin() return IRList::const_iterator. The skip_noops lambda declared its first parameter as IRList::iterator&, so the calls at the top of the loop did not match (no known conversion from const_iterator to iterator&), which broke the build on GCC (both linux and windows). Use IRList::const_iterator& for the iterator parameter so the lambda accepts the iterators that a const comparison actually works with.
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Hi, thanks for the feedback! This PR makes Could you please re-run the CI / take another look? Thanks! |
rootkiller6788
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August 27, 2026 18:05
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Fixes #778
IRList::structural_equalscompared every entry in the IR lists, includingMFLOW_FALLTHROUGHno-ops, so two methods that differ only in the placement of a no-op (e.g. an unreferenced label lowered to FALLTHROUGH) were reported as not structurally equal. Trailing metadata/no-op entries after the last real instruction also caused a mismatch when the other list had already been fully consumed.This change skips metadata and FALLTHROUGH entries on both sides before each comparison step, and skips any remaining trailing no-ops after the main loop. Unit tests are added for leading and trailing FALLTHROUGH entries, plus a negative case ensuring real differences are still detected.