[flang][openmp] Parallel reduction FIR lowering

This patch extends the logic for lowering loop construct reductions to parallel block reductions.

Reviewed By: kiranchandramohan

Differential Revision: https://reviews.llvm.org/D154182

flang/lib/Lower/Bridge.cpp

@@ -2172,6 +2172,8 @@ class FirConverter : public Fortran::lower::AbstractConverter {
 
     const Fortran::parser::OpenMPLoopConstruct *ompLoop =
         std::get_if<Fortran::parser::OpenMPLoopConstruct>(&omp.u);
+    const Fortran::parser::OpenMPBlockConstruct *ompBlock =
+        std::get_if<Fortran::parser::OpenMPBlockConstruct>(&omp.u);
 
     // If loop is part of an OpenMP Construct then the OpenMP dialect
     // workshare loop operation has already been created. Only the
@@ -2196,8 +2198,15 @@ class FirConverter : public Fortran::lower::AbstractConverter {
     for (Fortran::lower::pft::Evaluation &e : curEval->getNestedEvaluations())
       genFIR(e);
 
-    if (ompLoop)
+    if (ompLoop) {
       genOpenMPReduction(*this, *loopOpClauseList);
+    } else if (ompBlock) {
+      const auto &blockStart =
+          std::get<Fortran::parser::OmpBeginBlockDirective>(ompBlock->t);
+      const auto &blockClauses =
+          std::get<Fortran::parser::OmpClauseList>(blockStart.t);
+      genOpenMPReduction(*this, blockClauses);
+    }
 
     localSymbols.popScope();
     builder->restoreInsertionPoint(insertPt);