[CodeView] Emit the correct TypeIndex for std::nullptr_t.

The TypeIndex used by cl.exe is 0x103, which indicates a SimpleTypeMode
of NearPointer (note the absence of the bitness, normally pointers use a
mode of NearPointer32 or NearPointer64) and a SimpleTypeKind of void.
So this is basically a void*, but without a specified size, which makes
sense given how std::nullptr_t is defined.

clang-cl was actually not emitting *anything* for this. Instead, when we
encountered std::nullptr_t in a DIType, we would actually just emit a
TypeIndex of 0, which is obviously wrong.

std::nullptr_t in DWARF is represented as a DW_TAG_unspecified_type with
a name of "decltype(nullptr)", so we add that logic along with a test,
as well as an update to the dumping code so that we no longer print
void* when dumping 0x103 (which would previously treat Void/NearPointer
no differently than Void/NearPointer64).

Differential Revision: https://reviews.llvm.org/D53957

llvm-svn: 345811

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 42259d4..9b2b347 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -1516,6 +1516,8 @@ TypeIndex CodeViewDebug::lowerType(const DIType *Ty, const DIType *ClassTy) {
   case dwarf::DW_TAG_union_type:
     return lowerTypeUnion(cast<DICompositeType>(Ty));
   case dwarf::DW_TAG_unspecified_type:
+    if (Ty->getName() == "decltype(nullptr)")
+      return TypeIndex::NullptrT();
     return TypeIndex::None();
   default:
     // Use the null type index.