[CodeView] Allow empty types in member functions

Summary:
`CodeViewDebug::lowerTypeMemberFunction` used to default to a `Void`
return type if the function's type array was empty. After D54667, it
started blindly indexing the 0th item for the return type, which fails
in `getOperand` for empty arrays if assertions are enabled.

This patch restores the `Void` return type for empty type arrays, and
adds a test generated by Rust in line-only debuginfo mode.

Reviewers: zturner, rnk

Reviewed By: rnk

Subscribers: hiraditya, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D57070

llvm-svn: 351910

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 75ecd81f210..60731f1e676 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -1835,7 +1835,10 @@ TypeIndex CodeViewDebug::lowerTypeMemberFunction(const DISubroutineType *Ty,
 
   unsigned Index = 0;
   SmallVector<TypeIndex, 8> ArgTypeIndices;
-  TypeIndex ReturnTypeIndex = getTypeIndex(ReturnAndArgs[Index++]);
+  TypeIndex ReturnTypeIndex = TypeIndex::Void();
+  if (ReturnAndArgs.size() > Index) {
+    ReturnTypeIndex = getTypeIndex(ReturnAndArgs[Index++]);
+  }
 
   // If the first argument is a pointer type and this isn't a static method,
   // treat it as the special 'this' parameter, which is encoded separately from