[flang][OpenMP] Upstream lowering of OpenMP `Flush` construct

[SouraVX]

Summary

Note: This patch reflects the work that can be upstreamed from PR's(merged):

• https://github.com/flang-compiler/f18-llvm-project/pull/476

[clementval]

LGTM

[kiranchandramohan]

flang/lib/Lower/OpenMP.cpp

112

Is this variable used? Would it give a warning and cause a failure in the Werror enabled bots?

[SouraVX]

After this patch both LLVM Master and FIR-dev branches will be in sync.

[SouraVX]

flang/lib/Lower/OpenMP.cpp

112

Yes the warning comes and failure may happen. But nobody mentioned this on FIR-dev ?
But let me reconfirm? is this flag Werror enabled by default on all LLVM bots ? if so let me remove this.

[SouraVX]

Removed ununsed variable.

[awarzynski]

flang/lib/Lower/OpenMP.cpp

112

Two out three of our buildbots have Werror enabled for Flang:

• https://github.com/llvm/llvm-zorg/blob/e8ba87e92b857c14b7eb5466c4266a9e09a1f5fb/buildbot/osuosl/master/config/builders.py#L1515-L1558

As you can see one uses clang-10 and the other gcc-10. Hope this helps!

[kiranchandramohan]

flang/lib/Lower/OpenMP.cpp

112

Thanks @awarzynski.

112

I think we discussed the Werror setting when we were upstreaming Flang to LLVM. The LLVM default behaviour is not setting Werror. But Flang developers were of the opinion that it is a very useful flag to have to ensure that the codebase remains warning free and thus maintained at a high standard. So we decided to have a separate FLANG_WERROR flag which is by default OFF but switched ON in our buildbots.

[SouraVX]

flang/lib/Lower/OpenMP.cpp

112

Thanks for quick reference :). I've updated the patch(removed the unused variable).

flang/lib/Lower/OpenMP.cpp

genOMP(Fortran::lower::AbstractConverter &converter,
        const Fortran::parser::OpenMPStandaloneConstruct &standaloneConstruct) {
   std::visit(
       Fortran::common::visitors{
           [&](const Fortran::parser::OpenMPSimpleStandaloneConstruct
                   &simpleStandaloneConstruct) {
             genOMP(converter, eval, simpleStandaloneConstruct);
           },
           [&](const Fortran::parser::OpenMPFlushConstruct &flushConstruct) {
-            TODO();
+            SmallVector<Value, 4> operandRange;
+            if (const auto &ompObjectList =
+                    std::get<std::optional<Fortran::parser::OmpObjectList>>(
+                        flushConstruct.t))
+              genObjectList(*ompObjectList, converter, operandRange);
+            if (std::get<std::optional<Fortran::parser::OmpFlushMemoryClause>>(
+                    flushConstruct.t))
+              TODO("Handle OmpFlushMemoryClause");
+            converter.getFirOpBuilder().create<mlir::omp::FlushOp>(
+                converter.getCurrentLocation(), operandRange);
           },
           [&](const Fortran::parser::OpenMPCancelConstruct &cancelConstruct) {
             TODO("");
           },
           [&](const Fortran::parser::OpenMPCancellationPointConstruct
                   &cancellationPointConstruct) { TODO(""); },
       },
       standaloneConstruct.u);