[flang][debug] Support fixed size character type. (llvm#95462)

This PR adds debug support for fixed size character type. The character
type gets translated to DIStringType.

As I have noticed in comments, currently DIStringType does not have a
way to represent the underlying character type of the string. This
restricts our ability to represent wide string. As an example, this is
how the debugger shows 2 different type of string. Note that non-ascii
characters work ok with default kind string.

  character(kind=4, len=5) :: str1
  character(len=16) :: str2
  str1 = 'hello'
  str2 = 'π = 3.14'

(gdb) p str1
$1 = 'h\000\000\000e\000\000\000l\000\000\000l\000\000\000o\000\000\000'

(gdb) p str2
$2 = 'π = 3.14       '

Author: abidh

flang/lib/Optimizer/Transforms/DebugTypeGenerator.cpp

@@ -190,6 +190,33 @@ mlir::LLVM::DITypeAttr DebugTypeGenerator::convertSequenceType(
       /* associated */ nullptr);
 }
 
+mlir::LLVM::DITypeAttr DebugTypeGenerator::convertCharacterType(
+    fir::CharacterType charTy, mlir::LLVM::DIFileAttr fileAttr,
+    mlir::LLVM::DIScopeAttr scope, mlir::Location loc) {
+  mlir::MLIRContext *context = module.getContext();
+  if (!charTy.hasConstantLen())
+    return genPlaceholderType(context);
+
+  // DWARF 5 says the following about the character encoding in 5.1.1.2.
+  // "DW_ATE_ASCII and DW_ATE_UCS specify encodings for the Fortran 2003
+  // string kinds ASCII (ISO/IEC 646:1991) and ISO_10646 (UCS-4 in ISO/IEC
+  // 10646:2000)."
+  unsigned encoding = llvm::dwarf::DW_ATE_ASCII;
+  if (charTy.getFKind() != 1)
+    encoding = llvm::dwarf::DW_ATE_UCS;
+
+  // FIXME: Currently the DIStringType in llvm does not have the option to set
+  // type of the underlying character. This restricts out ability to represent
+  // string with non-default characters. Please see issue #95440 for more
+  // details.
+  return mlir::LLVM::DIStringTypeAttr::get(
+      context, llvm::dwarf::DW_TAG_string_type,
+      mlir::StringAttr::get(context, ""),
+      charTy.getLen() * kindMapping.getCharacterBitsize(charTy.getFKind()),
+      /*alignInBits=*/0, /*stringLength=*/nullptr,
+      /*stringLengthExp=*/nullptr, /*stringLocationExp=*/nullptr, encoding);
+}
+
 mlir::LLVM::DITypeAttr
 DebugTypeGenerator::convertType(mlir::Type Ty, mlir::LLVM::DIFileAttr fileAttr,
                                 mlir::LLVM::DIScopeAttr scope,
@@ -224,6 +251,8 @@ DebugTypeGenerator::convertType(mlir::Type Ty, mlir::LLVM::DIFileAttr fileAttr,
                         bitWidth * 2, llvm::dwarf::DW_ATE_complex_float);
   } else if (auto seqTy = mlir::dyn_cast_or_null<fir::SequenceType>(Ty)) {
     return convertSequenceType(seqTy, fileAttr, scope, loc);
+  } else if (auto charTy = mlir::dyn_cast_or_null<fir::CharacterType>(Ty)) {
+    return convertCharacterType(charTy, fileAttr, scope, loc);
   } else if (auto boxTy = mlir::dyn_cast_or_null<fir::BoxType>(Ty)) {
     auto elTy = boxTy.getElementType();
     if (auto seqTy = mlir::dyn_cast_or_null<fir::SequenceType>(elTy))

flang/lib/Optimizer/Transforms/DebugTypeGenerator.h

@@ -45,6 +45,10 @@ class DebugTypeGenerator {
                            mlir::LLVM::DIFileAttr fileAttr,
                            mlir::LLVM::DIScopeAttr scope, mlir::Location loc,
                            bool genAllocated, bool genAssociated);
+  mlir::LLVM::DITypeAttr convertCharacterType(fir::CharacterType charTy,
+                                              mlir::LLVM::DIFileAttr fileAttr,
+                                              mlir::LLVM::DIScopeAttr scope,
+                                              mlir::Location loc);
   mlir::ModuleOp module;
   KindMapping kindMapping;
   std::uint64_t dimsSize;

flang/test/Integration/debug-char-type-1.f90

@@ -0,0 +1,21 @@
+! RUN: %flang_fc1 -emit-llvm -debug-info-kind=standalone %s -o - | FileCheck  %s
+
+module helper
+  character(len=40) :: str
+end module helper
+
+program test
+  use helper
+  character(kind=4, len=8) :: first
+  character(len=10) :: second
+  first = '3.14 = π'
+  second = 'Fortran'
+  str = 'Hello World!'
+end program test
+
+! CHECK-DAG: !DIGlobalVariable(name: "str"{{.*}}type: ![[TY40:[0-9]+]]{{.*}})
+! CHECK-DAG: ![[TY40]] = !DIStringType(size: 320, encoding: DW_ATE_ASCII)
+! CHECK-DAG: !DILocalVariable(name: "first"{{.*}}type: ![[TY8:[0-9]+]])
+! CHECK-DAG: ![[TY8]] = !DIStringType(size: 256, encoding: DW_ATE_UCS)
+! CHECK-DAG: !DILocalVariable(name: "second"{{.*}}type: ![[TY10:[0-9]+]])
+! CHECK-DAG: ![[TY10]] = !DIStringType(size: 80, encoding: DW_ATE_ASCII)

flang/test/Transforms/debug-char-type-1.fir

@@ -0,0 +1,19 @@
+// RUN: fir-opt --add-debug-info --mlir-print-debuginfo %s | FileCheck %s
+
+module attributes {dlti.dl_spec = #dlti.dl_spec<>} {
+  fir.global @_QMhelperEstr1 : !fir.char<1,40> {
+    %0 = fir.zero_bits !fir.char<1,40>
+    fir.has_value %0 : !fir.char<1,40>
+  } loc(#loc1)
+  fir.global @_QMhelperEstr2 : !fir.char<4,20> {
+    %0 = fir.zero_bits !fir.char<4,20>
+    fir.has_value %0 : !fir.char<4,20>
+  } loc(#loc1)
+}
+#loc1 = loc("string.f90":1:1)
+
+// CHECK-DAG: #[[TY1:.*]] = #llvm.di_string_type<tag = DW_TAG_string_type, name = "", sizeInBits = 320, encoding = DW_ATE_ASCII>
+// CHECK-DAG: #llvm.di_global_variable<{{.*}}name = "str1"{{.*}}type = #[[TY1]]{{.*}}>
+// CHECK-DAG: #[[TY2:.*]] = #llvm.di_string_type<tag = DW_TAG_string_type, name = "", sizeInBits = 640, encoding = DW_ATE_UCS>
+// CHECK-DAG: #llvm.di_global_variable<{{.*}}name = "str2"{{.*}}type = #[[TY2]]{{.*}}>
+