[mlir][flang] Improve handling of fortran module variables.

Currently, only those global variables which are at compile unit scope
are added to the 'Globals' list of the compile unit. This does not work
for module variables of fortran where hierarchy can be
variable -> module -> compile unit.

To fix this, if a variable scope points to a module, we walk one level
up and see if module is in the compile unit scope.

This was initially part of llvm#91582 which adds debug information for
fortran module variables. Kiran pointed out that MLIR changes should
go in separate PRs.

Author: abidh

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -1029,11 +1029,17 @@ LogicalResult ModuleTranslation::convertGlobals() {
           debugTranslation->translateGlobalVariableExpression(op.getDbgExpr());
       llvm::DIGlobalVariable *diGlobalVar = diGlobalExpr->getVariable();
       var->addDebugInfo(diGlobalExpr);
+      // For fortran, the scope hierarchy can be
+      // variable -> module -> compile unit
+      // If a variable scope points to Module then we get its parent scope so
+      // that globals get added to the compile unit.
+      llvm::DIScope *scope = diGlobalVar->getScope();
+      if (llvm::DIModule *mod = dyn_cast_if_present<llvm::DIModule>(scope))
+        scope = mod->getScope();
 
       // Get the compile unit (scope) of the the global variable.
       if (llvm::DICompileUnit *compileUnit =
-              dyn_cast_if_present<llvm::DICompileUnit>(
-                  diGlobalVar->getScope())) {
+              dyn_cast_if_present<llvm::DICompileUnit>(scope)) {
         // Update the compile unit with this incoming global variable expression
         // during the finalizing step later.
         allGVars[compileUnit].push_back(diGlobalExpr);

mlir/test/Target/LLVMIR/llvmir-debug.mlir

@@ -311,6 +311,29 @@ llvm.mlir.global external @global_with_expr_2() {addr_space = 0 : i32, dbg_expr
 
 // -----
 
+// CHECK: @module_global_1 = external global i64, !dbg {{.*}}
+// CHECK: @module_global_2 = external global i64, !dbg {{.*}}
+// CHECK: !llvm.module.flags = !{{{.*}}}
+// CHECK: !llvm.dbg.cu = !{{{.*}}}
+// CHECK-DAG: ![[FILE:.*]] = !DIFile(filename: "test.f90", directory: "existence")
+// CHECK-DAG: ![[TYPE:.*]] = !DIBasicType(name: "integer", size: 64, encoding: DW_ATE_signed)
+// CHECK-DAG: ![[SCOPE:.*]] = distinct !DICompileUnit(language: DW_LANG_Fortran95, file: ![[FILE]], producer: "MLIR", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: ![[GVALS:.*]])
+// CHECK-DAG: ![[SCOPE1:.*]] = !DIModule(scope: ![[SCOPE]], name: "module2", file: ![[FILE]], line: 120)
+// CHECK-DAG: ![[GVAR0:.*]] = distinct !DIGlobalVariable(name: "module_global_1", linkageName: "module_global_1", scope: ![[SCOPE1]], file: ![[FILE]], line: 121, type: ![[TYPE]], isLocal: false, isDefinition: true)
+// CHECK-DAG: ![[GVAR1:.*]] = distinct !DIGlobalVariable(name: "module_global_2", linkageName: "module_global_2", scope: ![[SCOPE1]], file: ![[FILE]], line: 122, type: ![[TYPE]], isLocal: false, isDefinition: true)
+// CHECK-DAG: ![[GEXPR0:.*]] = !DIGlobalVariableExpression(var: ![[GVAR0]], expr: !DIExpression())
+// CHECK-DAG: ![[GEXPR1:.*]] = !DIGlobalVariableExpression(var: ![[GVAR1]], expr: !DIExpression())
+// CHECK-DAG: ![[GVALS]] = !{![[GEXPR0]], ![[GEXPR1]]}
+
+#di_file = #llvm.di_file<"test.f90" in "existence">
+#di_compile_unit = #llvm.di_compile_unit<id = distinct[0]<>, sourceLanguage = DW_LANG_Fortran95, file = #di_file, producer = "MLIR", isOptimized = true, emissionKind = Full>
+#di_basic_type = #llvm.di_basic_type<tag = DW_TAG_base_type, name = "integer", sizeInBits = 64, encoding = DW_ATE_signed>
+#di_module = #llvm.di_module<file = #di_file, scope = #di_compile_unit, name = "module2", configMacros = "", includePath = "", apinotes = "", line = 120, isDecl = false >
+llvm.mlir.global external @module_global_1() {dbg_expr = #llvm.di_global_variable_expression<var = <scope = #di_module, name = "module_global_1", linkageName = "module_global_1", file = #di_file, line = 121, type = #di_basic_type, isLocalToUnit = false, isDefined = true>, expr = <>>} : i64
+llvm.mlir.global external @module_global_2() {dbg_expr = #llvm.di_global_variable_expression<var = <scope = #di_module, name = "module_global_2", linkageName = "module_global_2", file = #di_file, line = 122, type = #di_basic_type, isLocalToUnit = false, isDefined = true>, expr = <>>} : i64
+
+// -----
+
 // Nameless and scopeless global constant.
 
 // CHECK-LABEL: @.str.1 = external constant [10 x i8]