[flang] Introduce stub targets for the lowering of Open MP directives in the flang bridge to MLIR

[schweitz]

Summary

These are simple stubs for now.

The lowering bridge walks the front-end parse trees via the PFT and generates an operational specification of the input as MLIR. Several productions in the parse trees relate to Open MP directives. The bridge will need to process those directives, via these calls, and generate the appropriate OpenMP dialect Ops in MLIR.

The bridge to these stubs will be part of a future revision.

[kiranchandramohan]

Thanks @schweitz for this stub. It will be a good place to start for the OpenMP lowering.

flang/include/flang/Lower/AbstractConverter.h

+//===-- Lower/AbstractConverter.h -------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_LOWER_ABSTRACTCONVERTER_H
+#define FORTRAN_LOWER_ABSTRACTCONVERTER_H
+
+namespace Fortran::lower {
+
+// temporary stub
+class AbstractConverter;
+
+} // namespace Fortran::lower
+
+#endif // FORTRAN_LOWER_ABSTRACTCONVERTER_H

flang/include/flang/Lower/OpenMP.h

+//===-- Lower/OpenMP.h -- lower Open MP directives --------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_LOWER_OPENMP_H
+#define FORTRAN_LOWER_OPENMP_H
+
+namespace Fortran {
+namespace parser {
+struct OpenMPConstruct;
+struct OmpEndLoopDirective;
+} // namespace parser
+
+namespace lower {
+
+class AbstractConverter;
+
+namespace pft {
+struct Evaluation;
+} // namespace pft
+
+void genOpenMPConstruct(AbstractConverter &, pft::Evaluation &,
+                        const parser::OpenMPConstruct &);
+
+void genOpenMPEndLoop(AbstractConverter &, pft::Evaluation &,
+                      const parser::OmpEndLoopDirective &);
+
+} // namespace lower
+} // namespace Fortran
+
+#endif // FORTRAN_LOWER_OPENMP_H

flang/lib/Lower/CMakeLists.txt

 
 add_flang_library(FortranLower
+  OpenMP.cpp
   PFTBuilder.cpp
 
   LINK_COMPONENTS
   Support
 )

flang/lib/Lower/OpenMP.cpp

+//===-- OpenMP.cpp -- Open MP directive lowering --------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "flang/Lower/OpenMP.h"
+#include "flang/Lower/AbstractConverter.h"
+#include "flang/Lower/PFTBuilder.h"
+#include "flang/Parser/parse-tree.h"
+
+#define TODO() llvm_unreachable("not yet implemented")
+
+void Fortran::lower::genOpenMPConstruct(
+    Fortran::lower::AbstractConverter &, Fortran::lower::pft::Evaluation &,
+    const Fortran::parser::OpenMPConstruct &) {
+  TODO();
+}
+
+void Fortran::lower::genOpenMPEndLoop(
+    Fortran::lower::AbstractConverter &, Fortran::lower::pft::Evaluation &,
+    const Fortran::parser::OmpEndLoopDirective &) {
+  TODO();
+}