Make CompilerType::getBitSize() / getByteSize() return an optional result. NFC

The code in LLDB assumes that CompilerType and friends use the size 0
as a sentinel value to signal an error. This works for C++, where no
zero-sized type exists, but in many other programming languages
(including I believe C) types of size zero are possible and even
common. This is a particular pain point in swift-lldb, where extra
code exists to double-check that a type is *really* of size zero and
not an error at various locations.

To remedy this situation, this patch starts by converting
CompilerType::getBitSize() and getByteSize() to return an optional
result. To avoid wasting space, I hand-rolled my own optional data
type assuming that no type is larger than what fits into 63
bits. Follow-up patches would make similar changes to the ValueObject
hierarchy.

rdar://problem/47178964

Differential Revision: https://reviews.llvm.org/D56688

llvm-svn: 351214

1 files changed, 5 insertions, 4 deletions

diff --git a/lldb/source/Core/ValueObjectConstResult.cpp b/lldb/source/Core/ValueObjectConstResult.cpp
index e857702653e..f6e32c03b0e 100644
--- a/lldb/source/Core/ValueObjectConstResult.cpp
+++ b/lldb/source/Core/ValueObjectConstResult.cpp
@@ -198,10 +198,11 @@ lldb::ValueType ValueObjectConstResult::GetValueType() const {
 
 uint64_t ValueObjectConstResult::GetByteSize() {
   ExecutionContext exe_ctx(GetExecutionContextRef());
-
-  if (m_byte_size == 0)
-    SetByteSize(
-        GetCompilerType().GetByteSize(exe_ctx.GetBestExecutionContextScope()));
+  if (m_byte_size == 0) {
+    if (auto size =
+        GetCompilerType().GetByteSize(exe_ctx.GetBestExecutionContextScope()))
+      SetByteSize(*size);
+  }
   return m_byte_size;
 }