[flang][OpenMP] Added support for lowering OpenMP barrier construct

This patch adds lowering support for OpenMP barrier construct to
OpenMP Dialect operations.

In order to support lowering, this patch registers OpenMPDialect
and also adds OpenMPDialect to the legalizer.

Author: SouraVX

flang/include/flang/Optimizer/Dialect/FIRDialect.h

@@ -46,6 +46,7 @@ inline void registerFIR() {
     mlir::registerDialect<mlir::StandardOpsDialect>();
     mlir::registerDialect<mlir::vector::VectorDialect>();
     mlir::registerDialect<FIROpsDialect>();
+    mlir::registerDialect<mlir::omp::OpenMPDialect>();
     return true;
   }();
 }

flang/lib/Lower/OpenMP.cpp

@@ -8,15 +8,43 @@
 
 #include "flang/Lower/OpenMP.h"
 #include "flang/Lower/Bridge.h"
+#include "flang/Lower/FIRBuilder.h"
 #include "flang/Lower/PFTBuilder.h"
 #include "flang/Parser/parse-tree.h"
+#include "mlir/Dialect/OpenMP/OpenMPDialect.h"
+#include "mlir/IR/Builders.h"
+#include "mlir/IR/Module.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/MD5.h"
 
 #define TODO() llvm_unreachable("not yet implemented")
 
 void Fortran::lower::genOpenMPConstruct(
-    Fortran::lower::AbstractConverter &, Fortran::lower::pft::Evaluation &,
-    const Fortran::parser::OpenMPConstruct &) {
-  TODO();
+    Fortran::lower::AbstractConverter &ABSConv,
+    Fortran::lower::pft::Evaluation &Eval,
+    const Fortran::parser::OpenMPConstruct &OMPConstruct) {
+  if (auto StandaloneConstruct =
+          std::get_if<Fortran::parser::OpenMPStandaloneConstruct>(
+              &OMPConstruct.u)) {
+
+    if (auto SimpleStandaloneConstruct =
+            std::get_if<Fortran::parser::OpenMPSimpleStandaloneConstruct>(
+                &StandaloneConstruct->u)) {
+      const auto &Directive{
+          std::get<Fortran::parser::OmpSimpleStandaloneDirective>(
+              SimpleStandaloneConstruct->t)};
+      switch (Directive.v) {
+      default:
+        TODO();
+      case parser::OmpSimpleStandaloneDirective::Directive::Barrier: {
+        ABSConv.getFirOpBuilder().create<mlir::omp::BarrierOp>(
+            ABSConv.getCurrentLocation());
+        break;
+      }
+      }
+    }
+  }
 }
 
 void Fortran::lower::genOpenMPEndLoop(

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -2697,6 +2697,7 @@ struct FIRToLLVMLoweringPass
     mlir::populateStdToLLVMConversionPatterns(typeConverter, pattern);
     mlir::ConversionTarget target{*context};
     target.addLegalDialect<mlir::LLVM::LLVMDialect>();
+    target.addLegalDialect<mlir::omp::OpenMPDialect>();
 
     // required NOPs for applying a full conversion
     target.addLegalOp<mlir::ModuleOp, mlir::ModuleTerminatorOp>();

flang/test/Lower/omp-barrier.f90

@@ -0,0 +1,24 @@
+! This test checks lowering of OpenMP Barrier Directive.
+
+! RUN: bbc -fopenmp -emit-fir %s -o - | \
+! RUN:   FileCheck %s --check-prefix=FIRDialect
+! RUN: bbc -fopenmp -emit-llvm %s -o - | \
+! RUN:   FileCheck %s --check-prefix=LLVMIRDialect
+! RUN: bbc -fopenmp -emit-llvm %s -o - | \
+! RUN:   mlir-translate -mlir-to-llvmir - | FileCheck %s --check-prefix=LLVMIR
+
+program barrier
+
+        integer :: a,b,c
+
+!$OMP BARRIER
+!FIRDialect: omp.barrier
+!LLVMIRDialect: omp.barrier
+!LLVMIR: call void @__kmpc_barrier(%struct.ident_t* @1, i32 %omp_global_thread_num)
+        c = a + b
+!$OMP BARRIER
+!FIRDialect: omp.barrier
+!LLVMIRDialect: omp.barrier
+!LLVMIR: call void @__kmpc_barrier(%struct.ident_t* @1, i32 %omp_global_thread_num1)
+
+end program