[flang-commits] [clang] [flang] [flang][OpenMP] Upstream first part of `do concurrent` mapping (PR #126026)

[Tarun Prabhu via flang-commits]

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+<!--===- docs/DoConcurrentMappingToOpenMP.md
+
+   Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+   See https://llvm.org/LICENSE.txt for license information.
+   SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+-->
+
+# `DO CONCURRENT` mapping to OpenMP
+
+```{contents}
+---
+local:
+---
+```
+
+This document seeks to describe the effort to parallelize `do concurrent` loops
+by mapping them to OpenMP worksharing constructs. The goals of this document
+are:
+* Describing how to instruct `flang` to map `DO CONCURRENT` loops to OpenMP
+  constructs.
+* Tracking the current status of such mapping.
+* Describing the limitations of the current implementation.
+* Describing next steps.
+* Tracking the current upstreaming status (from the AMD ROCm fork).
+
+## Usage
+
+In order to enable `do concurrent` to OpenMP mapping, `flang` adds a new
+compiler flag: `-fdo-concurrent-to-openmp`. This flag has 3 possible values:
+1. `host`: this maps `do concurrent` loops to run in parallel on the host CPU.
+   This maps such loops to the equivalent of `omp parallel do`.
+2. `device`: this maps `do concurrent` loops to run in parallel on a target device.
+   This maps such loops to the equivalent of
+   `omp target teams distribute parallel do`.
+3. `none`: this disables `do concurrent` mapping altogether. In that case, such
+   loops are emitted as sequential loops.
+
+The above compiler switch is currently available only when OpenMP is also
----------------
tarunprabhu wrote:

NIT: Consider replacing above with the actual compiler switch. It feels slightly more readable to me.

```suggestion
The `-fdo-concurrent-to-openmp` compiler switch is currently available only when OpenMP is also
```

https://github.com/llvm/llvm-project/pull/126026