[flang][debug] Set scope of internal functions correctly.

The functions internal to subroutine should have the scope set to the
parent function. This allows to evaluate variable in parent when control
is stopped in the child.

Fixes #96314

Author: abidh

flang/lib/Optimizer/Transforms/AddDebugInfo.cpp

@@ -306,9 +306,29 @@ void AddDebugInfoPass::runOnOperation() {
           subprogramFlags | mlir::LLVM::DISubprogramFlags::Definition;
     }
     unsigned line = getLineFromLoc(l);
-    if (!result.second.modules.empty())
+    if (fir::isInternalProcedure(funcOp)) {
+      // For contained functions, the scope is the parent subroutine.
+      mlir::SymbolRefAttr sym = mlir::cast<mlir::SymbolRefAttr>(
+          funcOp->getAttr(fir::getHostSymbolAttrName()));
+      if (sym) {
+        if (auto func = symbolTable.lookup<mlir::func::FuncOp>(
+                sym.getLeafReference())) {
+          // FIXME: Can there be situation where we process contained function
+          // before the parent?
+          if (debugInfoIsAlreadySet(func.getLoc())) {
+            if (auto fusedLoc = mlir::cast<mlir::FusedLoc>(func.getLoc())) {
+              if (auto spAttr =
+                      mlir::dyn_cast_if_present<mlir::LLVM::DISubprogramAttr>(
+                          fusedLoc.getMetadata()))
+                Scope = spAttr;
+            }
+          }
+        }
+      }
+    } else if (!result.second.modules.empty()) {
       Scope = getOrCreateModuleAttr(result.second.modules[0], fileAttr, cuAttr,
                                     line - 1, false);
+    }
 
     auto spAttr = mlir::LLVM::DISubprogramAttr::get(
         context, id, compilationUnit, Scope, funcName, fullName, funcFileAttr,

flang/test/Transforms/debug-96314.fir

@@ -0,0 +1,26 @@
+// RUN: fir-opt --add-debug-info --mlir-print-debuginfo %s -o - | FileCheck %s
+
+module attributes {dlti.dl_spec = #dlti.dl_spec<>} {
+  func.func @_QMhelperPmod_sub(%arg0: !fir.ref<i32> {fir.bindc_name = "a"} ) {
+    return
+  } loc(#loc1)
+  func.func private @_QMhelperFmod_subPchild1(%arg0: !fir.ref<i32> {fir.bindc_name = "b"} ) attributes {fir.host_symbol = @_QMhelperPmod_sub, llvm.linkage = #llvm.linkage<internal>} {
+    return
+  } loc(#loc2)
+  func.func @global_sub_(%arg0: !fir.ref<i32> {fir.bindc_name = "n"} ) attributes {fir.internal_name = "_QPglobal_sub"} {
+    return
+  } loc(#loc3)
+  func.func private @_QFglobal_subPchild2(%arg0: !fir.ref<i32> {fir.bindc_name = "c"}) attributes {fir.host_symbol = @global_sub_, llvm.linkage = #llvm.linkage<internal>} {
+    return
+  } loc(#loc4)
+}
+
+#loc1 = loc("test.f90":5:1)
+#loc2 = loc("test.f90":15:1)
+#loc3 = loc("test.f90":25:1)
+#loc4 = loc("test.f90":35:1)
+
+// CHECK-DAG: #[[SP1:.*]] = #llvm.di_subprogram<{{.*}}name = "mod_sub"{{.*}}>
+// CHECK-DAG: #llvm.di_subprogram<{{.*}}scope = #[[SP1]], name = "child1"{{.*}}>
+// CHECK-DAG: #[[SP2:.*]] = #llvm.di_subprogram<{{.*}}linkageName = "global_sub_"{{.*}}>
+// CHECK-DAG: #llvm.di_subprogram<{{.*}}scope = #[[SP2]], name = "child2"{{.*}}>