[all-commits] [llvm/llvm-project] c5fbab: [flang][OpenMP] Semantic checks for metadirective ...

[Chi-Chun, Chen via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c5fbabb36e9be13e001cc6b96bfef7b4db33210d
      https://github.com/llvm/llvm-project/commit/c5fbabb36e9be13e001cc6b96bfef7b4db33210d
  Author: Chi-Chun, Chen <chichun.chen at hpe.com>
  Date:   2026-07-10 (Fri, 10 Jul 2026)

  Changed paths:
    M flang/lib/Semantics/check-omp-structure.cpp
    M flang/lib/Semantics/check-omp-structure.h
    M flang/lib/Semantics/check-omp-variant.cpp
    A flang/test/Semantics/OpenMP/metadirective-loop-applicability.f90
    A flang/test/Semantics/OpenMP/metadirective-loop-nest.f90
    A flang/test/Semantics/OpenMP/metadirective-loop-sequence.f90

  Log Message:
  -----------
  [flang][OpenMP] Semantic checks for metadirective loop nests (#207088)

A loop-associated metadirective variant (`do`, `simd`, ...) is only
resolved during lowering, so it is never checked as a loop construct
during semantic analysis. A malformed or non-canonical associated nest
therefore reaches lowering, which assumes a canonical nest.

This patch validates the nest that follows such a variant (the next
executable construct) during semantics, reusing the diagnostics of a
real loop-associated construct. Each applicable variant is checked
against it:

* Canonical loop: the affected loop must be a canonical DO loop, so a
`DO WHILE`, a pre-6.0 `DO CONCURRENT`, or a `DO` without loop control is
rejected.
* Nest depth: `collapse(n)` and `ordered(n)` must not exceed the depth
of the associated loop nest.
* Rectangularity: loops that must be rectangular (e.g. under `tile`) may
not have bounds that depend on an outer loop's variable.

A loop-associated variant may also have no loop nest at all. This
happens when the metadirective ends the execution part or a non-loop
construct follows it. Such a variant is rejected like a bare loop
directive with no associated loop.

Only variants that could be selected are checked: when a target is
known, a WHEN variant whose device or implementation selector cannot
match it is skipped (runtime `user` conditions never cause a skip).

Part of the feature work for #188820. Builds on top of
[#193664](https://github.com/llvm/llvm-project/issues/193664) and
[#194424](https://github.com/llvm/llvm-project/pull/194424).

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