[Flang][OpenMP] Fix for error in atomic read for different elements of the common symbol #80399 (#109265)

Fixes issue #80399

Author: chandankds

flang/lib/Semantics/check-omp-structure.cpp

@@ -1837,9 +1837,23 @@ inline void OmpStructureChecker::ErrIfLHSAndRHSSymbolsMatch(
     const Symbol &varSymbol = vSyms.front();
     for (const Symbol &symbol : evaluate::GetSymbolVector(*e)) {
       if (varSymbol == symbol) {
-        context_.Say(expr.source,
-            "RHS expression on atomic assignment statement cannot access '%s'"_err_en_US,
-            var.GetSource().ToString());
+        const Fortran::common::Indirection<Fortran::parser::Designator>
+            *designator = std::get_if<
+                Fortran::common::Indirection<Fortran::parser::Designator>>(
+                &expr.u);
+        if (designator) {
+          auto *z{var.typedExpr.get()};
+          auto *c{expr.typedExpr.get()};
+          if (z->v == c->v) {
+            context_.Say(expr.source,
+                "RHS expression on atomic assignment statement cannot access '%s'"_err_en_US,
+                var.GetSource());
+          }
+        } else {
+          context_.Say(expr.source,
+              "RHS expression on atomic assignment statement cannot access '%s'"_err_en_US,
+              var.GetSource());
+        }
       }
     }
   }

flang/test/Semantics/OpenMP/omp-atomic-assignment-stmt-read.f90

@@ -0,0 +1,41 @@
+! RUN: %flang_fc1 -fopenmp %s -o -
+
+integer :: x, vv(2), xx(2)
+type t1
+  integer :: v,y,yy(2)
+end type t1
+type(t1)::t,tt(2)
+x=1
+xx=1
+vv=1
+t%y=1
+t%yy=1
+tt(1)%y=1
+tt(1)%yy=1
+tt(2)%v=1
+tt(2)%y=1
+tt(2)%yy=1
+
+!$omp atomic read
+  vv(1) = vv(2)
+!$omp atomic read
+  t%v = t%y
+!$omp atomic read
+  t%v = t%yy(1)
+!$omp atomic read
+  tt(1)%v = tt(1)%y
+!$omp atomic read
+  tt(1)%v = tt(2)%v
+!$omp atomic read
+  tt(1)%v = tt(1)%yy(1)
+!$omp atomic read
+  t%yy(2) = t%y
+!$omp atomic read
+  t%yy(2) = t%yy(1)
+!$omp atomic read
+  tt(1)%yy(2) = tt(1)%y
+!$omp atomic read
+  tt(1)%yy(2) = tt(1)%yy(1)
+!$omp atomic read
+  tt(1)%yy(2) = tt(2)%yy(2)
+end