[lldb][TypeSystemClang][NFC] Clean up TypeSystemClang::GetBitSize (llvm#100674)

This patch performs following NFC changes to
TypeSystemClang::GetBitSize:
* Factor out the Objective-C logic into a helper function.
* Introduce a new case for `FunctionProto`. I don't see a good reason
for special-casing this in the `default` case.
* We had a redundant check for `GetCompleteType` in the `RecordType`
case. We used to allow zero-size types for records and function
prototypes, so we can just fold them into the same case.
* Introduce a new case for `IncompleteArray`.

The motivation for this is that there are a few issues around VLAs
(i.e., `Type::IncompleteArray`) whose fixes will be easier to reason
about after this refactor.

Generally I don't think treating a type with 0 size as an error is the
right thing to do (at least not for array types). But that's not
something I wanted to fold into this NFC change.

(cherry picked from commit 11a7ee5)

Author: Michael137

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

@@ -4915,67 +4915,68 @@ TypeSystemClang::GetFloatTypeSemantics(size_t byte_size) {
   return llvm::APFloatBase::Bogus();
 }
 
+std::optional<uint64_t>
+TypeSystemClang::GetObjCBitSize(QualType qual_type,
+                                ExecutionContextScope *exe_scope) {
+  assert(qual_type->isObjCObjectOrInterfaceType());
+  ExecutionContext exe_ctx(exe_scope);
+  if (Process *process = exe_ctx.GetProcessPtr()) {
+    if (ObjCLanguageRuntime *objc_runtime =
+            ObjCLanguageRuntime::Get(*process)) {
+      if (std::optional<uint64_t> bit_size =
+              objc_runtime->GetTypeBitSize(GetType(qual_type)))
+        return *bit_size;
+    }
+  } else {
+    static bool g_printed = false;
+    if (!g_printed) {
+      StreamString s;
+      DumpTypeDescription(qual_type.getAsOpaquePtr(), s);
+
+      llvm::outs() << "warning: trying to determine the size of type ";
+      llvm::outs() << s.GetString() << "\n";
+      llvm::outs() << "without a valid ExecutionContext. this is not "
+                      "reliable. please file a bug against LLDB.\n";
+      llvm::outs() << "backtrace:\n";
+      llvm::sys::PrintStackTrace(llvm::outs());
+      llvm::outs() << "\n";
+      g_printed = true;
+    }
+  }
+
+  return getASTContext().getTypeSize(qual_type) +
+         getASTContext().getTypeSize(getASTContext().ObjCBuiltinClassTy);
+}
+
 std::optional<uint64_t>
 TypeSystemClang::GetBitSize(lldb::opaque_compiler_type_t type,
                             ExecutionContextScope *exe_scope) {
-  if (GetCompleteType(type)) {
-    clang::QualType qual_type(GetCanonicalQualType(type));
-    const clang::Type::TypeClass type_class = qual_type->getTypeClass();
-    switch (type_class) {
-    case clang::Type::Record:
-      if (GetCompleteType(type))
-        return getASTContext().getTypeSize(qual_type);
-      else
-        return std::nullopt;
-      break;
+  if (!GetCompleteType(type))
+    return std::nullopt;
 
-    case clang::Type::ObjCInterface:
-    case clang::Type::ObjCObject: {
-      ExecutionContext exe_ctx(exe_scope);
-      Process *process = exe_ctx.GetProcessPtr();
-      if (process) {
-        if (ObjCLanguageRuntime *objc_runtime =
-                ObjCLanguageRuntime::Get(*process)) {
-          if (std::optional<uint64_t> bit_size =
-                  objc_runtime->GetTypeBitSize(GetType(qual_type)))
-            return *bit_size;
-        }
-      } else {
-        static bool g_printed = false;
-        if (!g_printed) {
-          StreamString s;
-          DumpTypeDescription(type, s);
-
-          llvm::outs() << "warning: trying to determine the size of type ";
-          llvm::outs() << s.GetString() << "\n";
-          llvm::outs() << "without a valid ExecutionContext. this is not "
-                          "reliable. please file a bug against LLDB.\n";
-          llvm::outs() << "backtrace:\n";
-          llvm::sys::PrintStackTrace(llvm::outs());
-          llvm::outs() << "\n";
-          g_printed = true;
-        }
-      }
-    }
-      [[fallthrough]];
-    default:
-      const uint32_t bit_size = getASTContext().getTypeSize(qual_type);
-      if (bit_size == 0) {
-        if (qual_type->isIncompleteArrayType())
-          return getASTContext().getTypeSize(
-              qual_type->getArrayElementTypeNoTypeQual()
-                  ->getCanonicalTypeUnqualified());
-      }
-      if (qual_type->isObjCObjectOrInterfaceType())
-        return bit_size +
-               getASTContext().getTypeSize(getASTContext().ObjCBuiltinClassTy);
-      // Function types actually have a size of 0, that's not an error.
-      if (qual_type->isFunctionProtoType())
-        return bit_size;
-      if (bit_size)
-        return bit_size;
-    }
+  clang::QualType qual_type(GetCanonicalQualType(type));
+  const clang::Type::TypeClass type_class = qual_type->getTypeClass();
+  switch (type_class) {
+  case clang::Type::FunctionProto:
+  case clang::Type::Record:
+    return getASTContext().getTypeSize(qual_type);
+  case clang::Type::ObjCInterface:
+  case clang::Type::ObjCObject:
+    return GetObjCBitSize(qual_type, exe_scope);
+  case clang::Type::IncompleteArray: {
+    const uint64_t bit_size = getASTContext().getTypeSize(qual_type);
+    if (bit_size == 0)
+      return getASTContext().getTypeSize(
+          qual_type->getArrayElementTypeNoTypeQual()
+              ->getCanonicalTypeUnqualified());
+
+    return bit_size;
+  }
+  default:
+    if (const uint64_t bit_size = getASTContext().getTypeSize(qual_type))
+      return bit_size;
   }
+
   return std::nullopt;
 }
 

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.h

@@ -1253,6 +1253,9 @@ class TypeSystemClang : public TypeSystem {
   /// on creation of a new instance.
   void LogCreation() const;
 
+  std::optional<uint64_t> GetObjCBitSize(clang::QualType qual_type,
+                                         ExecutionContextScope *exe_scope);
+
   // Classes that inherit from TypeSystemClang can see and modify these
   std::string m_target_triple;
   std::unique_ptr<clang::ASTContext> m_ast_up;