[flang][Lower] Treat directives with nested evaluations as constructs (#91614)

When generating block terminators in `genFIR(Evaluation)`, treat
`Directives` with nested evaluations the same way as `Constructs` to
determine the successor block.

This fixes #91526

Author: kparzysz

flang/lib/Lower/Bridge.cpp

@@ -4548,9 +4548,13 @@ class FirConverter : public Fortran::lower::AbstractConverter {
     // constructs, this can be done for either the end construct statement,
     // or for the construct itself, which will skip this code if the
     // end statement was visited first and generated a branch.
-    Fortran::lower::pft::Evaluation *successor =
-        eval.isConstruct() ? eval.getLastNestedEvaluation().lexicalSuccessor
-                           : eval.lexicalSuccessor;
+    Fortran::lower::pft::Evaluation *successor = [&]() {
+      if (eval.isConstruct() ||
+          (eval.isDirective() && eval.hasNestedEvaluations()))
+        return eval.getLastNestedEvaluation().lexicalSuccessor;
+      return eval.lexicalSuccessor;
+    }();
+
     if (successor && blockIsUnterminated()) {
       if (successor->isIntermediateConstructStmt() &&
           successor->parentConstruct->lowerAsUnstructured())

flang/test/Lower/branching-directive.f90

@@ -0,0 +1,25 @@
+!RUN: flang-new -fc1 -emit-hlfir -fopenmp -o - %s | FileCheck %s
+
+!https://github.com/llvm/llvm-project/issues/91526
+
+!CHECK:   cf.cond_br %{{[0-9]+}}, ^bb[[THEN:[0-9]+]], ^bb[[ELSE:[0-9]+]]
+!CHECK: ^bb[[THEN]]:
+!CHECK:   cf.br ^bb[[EXIT:[0-9]+]]
+!CHECK: ^bb[[ELSE]]:
+!CHECK:   fir.call @_FortranAStopStatement
+!CHECK:   fir.unreachable
+!CHECK: ^bb[[EXIT]]:
+
+subroutine simple(y)
+  implicit none
+  logical, intent(in) :: y
+  integer :: i
+  if (y) then
+!$omp parallel
+    i = 1
+!$omp end parallel
+  else
+    stop 1
+  end if
+end subroutine simple
+