[all-commits] [llvm/llvm-project] f99eba: [flang][OpenMP] Semantic checks for metadirective ...

[Chi-Chun, Chen via All-commits]

  Branch: refs/heads/users/cchen/flang-metadirective-loop-checks
  Home:   https://github.com/llvm/llvm-project
  Commit: f99eba8dae32864010703e4c2b1240ede51972dc
      https://github.com/llvm/llvm-project/commit/f99eba8dae32864010703e4c2b1240ede51972dc
  Author: Chi Chun, Chen <chichun.chen at hpe.com>
  Date:   2026-07-06 (Mon, 06 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

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).

Assisted with Copilot.


  Commit: 1b90243706bbd9c5f43ce96b6f25da31f79a6ed0
      https://github.com/llvm/llvm-project/commit/1b90243706bbd9c5f43ce96b6f25da31f79a6ed0
  Author: Chi Chun, Chen <chichun.chen at hpe.com>
  Date:   2026-07-06 (Mon, 06 Jul 2026)

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

  Log Message:
  -----------
  Skip loop checks for unselectable metadirective variants

A loop-associated METADIRECTIVE variant is only checked when it might be
selected on the compilation target. The static-applicability gate matched
device and implementation selectors, but it ignored two cases that make a
variant unselectable on any target:

- a user condition that folds to a compile-time false, and
- an unknown device or implementation property.

Such a variant still had its associated loop diagnosed even though it can
never be selected, so a valid program was rejected. Skip these variants in
the default match-all mode, where the impossible trait is decisive. The
match_any and match_none modes tolerate the trait, so they keep deferring
to context matching.

Assisted with Copilot.


Compare: https://github.com/llvm/llvm-project/compare/5652e59ad446...1b90243706bb

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