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, 2 deletions

diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
index 2827feb..f25391f 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcpp.cpp
@@ -297,8 +297,11 @@ bool lldb_private::formatters::LibStdcppWStringSummaryProvider(
       if (!wchar_compiler_type)
         return false;
 
-      const uint32_t wchar_size = wchar_compiler_type.GetBitSize(
-          nullptr); // Safe to pass NULL for exe_scope here
+      // Safe to pass nullptr for exe_scope here.
+      auto size = wchar_compiler_type.GetBitSize(nullptr);
+      if (!size)
+        return false;
+      const uint32_t wchar_size = *size;
 
       StringPrinter::ReadStringAndDumpToStreamOptions options(valobj);
       Status error;