llvm-project

70256dff - [flang][OpenMP] Support lowering of metadirective (part 2) (#194424)

[flang][OpenMP] Support lowering of metadirective (part 2) (#194424) Lower non-constant `user={condition(expr)}` selectors in OpenMP metadirectives to a runtime `fir.if` / `else` selection cascade. Dynamic user conditions are handled in two separate phases: - Static applicability uses only selector traits that are known at compile time. - Guarded ranking preserves selector specificity and dynamic-condition scores for the path where the runtime condition evaluates to true. Lowering first filters candidates using compile-time selector traits, then orders the remaining candidates with the normal OpenMP variant ranking rules. If the selected candidate has a non-constant user condition, that condition is emitted as a `fir.if` guard. When the condition evaluates to false, the `else` branch continues selection among the remaining candidates. For example: ```fortran !$omp metadirective & !$omp & when(user={condition(score(100): high)}: barrier) & !$omp & when(user={condition(low)}: taskwait) & !$omp & otherwise(nothing) ``` is selected as: ```text if (high) barrier else if (low) taskwait else nothing ``` Scores attached to dynamic `condition(score(...): expr)` selectors are preserved for the guarded candidate. As a result, those scores affect ranking only on the runtime path where the condition is true, instead of allowing a false runtime condition to influence unconditional selection. This also fixes the interactions with `extension(match_any)` and `extension(match_none)`: - `match_any` can be satisfied by a runtime condition when no static trait matches. - If static traits already satisfy `match_any`, the dynamic condition score is used only when the condition is true. - `match_none` keeps the dynamic condition inactive for static applicability while still preserving its score for ranking. For example, this `match_any` selector is statically applicable through `vendor(llvm)`, but the score on `flag` is used only when `flag` evaluates to true: ```fortran !$omp metadirective & !$omp & when(implementation={extension(match_any), vendor(llvm)}, & !$omp & user={condition(score(100): flag)}: barrier) & !$omp & when(user={condition(score(10): .true.)}: taskwait) & !$omp & otherwise(nothing) ``` is selected as: ```text if (flag) barrier else taskwait ``` The final fallback is the highest-ranked unguarded candidate, an explicit `otherwise` / `default` clause, or implicit `nothing`. This patch is part of the feature work for #188820 and is stacked on top of [#193664](https://github.com/llvm/llvm-project/pull/193664). Assisted with Copilot and GPT-5.4.