[flang][debug] Add debug type support for procedure pointers (#166764)

Fixes #161223

Procedure pointers in Fortran were generating incorrect debug type
information, showing as 'integer' in GDB instead of the actual procedure
signature.

Author: abidh

flang/lib/Optimizer/Transforms/DebugTypeGenerator.cpp

@@ -718,6 +718,31 @@ DebugTypeGenerator::convertType(mlir::Type Ty, mlir::LLVM::DIFileAttr fileAttr,
     return convertRecordType(recTy, fileAttr, scope, declOp);
   } else if (auto tupleTy = mlir::dyn_cast_if_present<mlir::TupleType>(Ty)) {
     return convertTupleType(tupleTy, fileAttr, scope, declOp);
+  } else if (mlir::isa<mlir::FunctionType>(Ty)) {
+    // Handle function types - these represent procedure pointers after the
+    // BoxedProcedure pass has run and unwrapped the fir.boxproc type, as well
+    // as dummy procedures (which are represented as function types in FIR)
+    llvm::SmallVector<mlir::LLVM::DITypeAttr> types;
+
+    auto funcTy = mlir::cast<mlir::FunctionType>(Ty);
+    // Add return type (or void if no return type)
+    if (funcTy.getNumResults() == 0)
+      types.push_back(mlir::LLVM::DINullTypeAttr::get(context));
+    else
+      types.push_back(
+          convertType(funcTy.getResult(0), fileAttr, scope, declOp));
+
+    for (mlir::Type paramTy : funcTy.getInputs())
+      types.push_back(convertType(paramTy, fileAttr, scope, declOp));
+
+    auto subroutineTy = mlir::LLVM::DISubroutineTypeAttr::get(
+        context, /*callingConvention=*/0, types);
+
+    return mlir::LLVM::DIDerivedTypeAttr::get(
+        context, llvm::dwarf::DW_TAG_pointer_type,
+        mlir::StringAttr::get(context, ""), subroutineTy,
+        /*sizeInBits=*/ptrSize * 8, /*alignInBits=*/0, /*offset=*/0,
+        /*optional<address space>=*/std::nullopt, /*extra data=*/nullptr);
   } else if (auto refTy = mlir::dyn_cast_if_present<fir::ReferenceType>(Ty)) {
     auto elTy = refTy.getEleTy();
     return convertPointerLikeType(elTy, fileAttr, scope, declOp,

flang/test/Integration/debug-proc-ptr-e2e.f90

@@ -0,0 +1,26 @@
+! RUN: %flang_fc1 -emit-llvm -debug-info-kind=standalone %s -o - | FileCheck %s
+
+program test_proc_ptr
+  implicit none
+  procedure(fun1), pointer :: fun_ptr
+
+  fun_ptr => fun1
+  print *, fun_ptr(3)
+
+contains
+  integer function fun1(x)
+    integer :: x
+    fun1 = x + 1
+  end function fun1
+end program test_proc_ptr
+
+! Check that fun_ptr is declared with correct type
+! CHECK-DAG: ![[INT:.*]] = !DIBasicType(name: "integer", size: 32, encoding: DW_ATE_signed)
+! CHECK-DAG: ![[PTR_INT:.*]] = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: ![[INT]], size: 64)
+
+! Check that fun_ptr variable is a pointer to a subroutine type
+! The order is: DILocalVariable -> pointer type -> subroutine type -> {return, params}
+! CHECK-DAG: ![[FUN_PTR_VAR:.*]] = !DILocalVariable(name: "fun_ptr", {{.*}}type: ![[PROC_PTR:[0-9]+]]
+! CHECK-DAG: ![[PROC_PTR]] = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: ![[SUBR_TYPE:[0-9]+]], size: 64)
+! CHECK-DAG: ![[SUBR_TYPE]] = !DISubroutineType(types: ![[SUBR_TYPES:[0-9]+]])
+! CHECK-DAG: ![[SUBR_TYPES]] = !{![[INT]], ![[PTR_INT]]}

flang/test/Transforms/debug-proc-ptr.fir

@@ -0,0 +1,41 @@
+// RUN: fir-opt --add-debug-info --mlir-print-debuginfo %s | FileCheck %s
+
+module {
+  func.func @_QQmain() attributes {fir.bindc_name = "test"} {
+    %0 = fir.alloca (!fir.ref<i32>) -> i32 {bindc_name = "fun_ptr", uniq_name = "_QFEfun_ptr"}
+    %1 = fircg.ext_declare %0 {uniq_name = "_QFEfun_ptr"} : (!fir.ref<(!fir.ref<i32>) -> i32>) -> !fir.ref<(!fir.ref<i32>) -> i32> loc(#loc1)
+
+    // Procedure pointer with no return: procedure(sub1), pointer :: sub_ptr
+    %2 = fir.alloca () -> () {bindc_name = "sub_ptr", uniq_name = "_QFEsub_ptr"}
+    %3 = fircg.ext_declare %2 {uniq_name = "_QFEsub_ptr"} : (!fir.ref<() -> ()>) -> !fir.ref<() -> ()> loc(#loc2)
+
+    // Procedure pointer with multiple args: procedure(func2), pointer :: func_ptr
+    %4 = fir.alloca (!fir.ref<i32>, !fir.ref<f64>) -> f32 {bindc_name = "func_ptr", uniq_name = "_QFEfunc_ptr"}
+    %5 = fircg.ext_declare %4 {uniq_name = "_QFEfunc_ptr"} : (!fir.ref<(!fir.ref<i32>, !fir.ref<f64>) -> f32>) -> !fir.ref<(!fir.ref<i32>, !fir.ref<f64>) -> f32> loc(#loc3)
+
+    return
+  } loc(#loc)
+}
+#loc = loc("test.f90":1:1)
+#loc1 = loc("test.f90":2:30)
+#loc2 = loc("test.f90":3:30)
+#loc3 = loc("test.f90":4:30)
+
+// CHECK-DAG: #[[INT:.*]] = #llvm.di_basic_type<tag = DW_TAG_base_type, name = "integer", sizeInBits = 32, encoding = DW_ATE_signed>
+// CHECK-DAG: #[[REAL32:.*]] = #llvm.di_basic_type<tag = DW_TAG_base_type, name = "real", sizeInBits = 32, encoding = DW_ATE_float>
+// CHECK-DAG: #[[REAL:.*]] = #llvm.di_basic_type<tag = DW_TAG_base_type, name = "real(kind=8)", sizeInBits = 64, encoding = DW_ATE_float>
+
+// CHECK-DAG: #[[PTR_INT:.*]] = #llvm.di_derived_type<tag = DW_TAG_pointer_type{{.*}}baseType = #[[INT]]{{.*}}>
+// CHECK-DAG: #[[PTR_REAL:.*]] = #llvm.di_derived_type<tag = DW_TAG_pointer_type{{.*}}baseType = #[[REAL]]{{.*}}>
+
+// CHECK-DAG: #[[SUB1:.*]] = #llvm.di_subroutine_type<types = #[[INT]], #[[PTR_INT]]>
+// CHECK-DAG: #[[PTR_SUB1:.*]] = #llvm.di_derived_type<tag = DW_TAG_pointer_type{{.*}}baseType = #[[SUB1]]{{.*}}>
+// CHECK-DAG: #llvm.di_local_variable<{{.*}}name = "fun_ptr"{{.*}}type = #[[PTR_SUB1]]{{.*}}>
+
+// CHECK-DAG: #di_subroutine_type{{.*}} = #llvm.di_subroutine_type<types = #di_null_type>
+// CHECK-DAG: #di_local_variable{{.*}} = #llvm.di_local_variable<{{.*}}name = "sub_ptr"{{.*}}type = #di_derived_type{{.*}}>
+// CHECK-DAG: #di_derived_type{{.*}} = #llvm.di_derived_type<tag = DW_TAG_pointer_type{{.*}}baseType = #di_subroutine_type{{.*}}{{.*}}>
+
+// CHECK-DAG: #[[SUB3:.*]] = #llvm.di_subroutine_type<types = #[[REAL32]], #[[PTR_INT]], #[[PTR_REAL]]>
+// CHECK-DAG: #[[PTR_SUB3:.*]] = #llvm.di_derived_type<tag = DW_TAG_pointer_type{{.*}}baseType = #[[SUB3]]{{.*}}>
+// CHECK-DAG: #llvm.di_local_variable<{{.*}}name = "func_ptr"{{.*}}type = #[[PTR_SUB3]]{{.*}}>