[CodeView] Allow empty types in member functions

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

@@ -1836,7 +1836,10 @@ 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

llvm/test/DebugInfo/COFF/types-empty-member-fn.ll

@@ -0,0 +1,72 @@
+; RUN: llc < %s -filetype=obj | llvm-readobj - -codeview | FileCheck %s
+
+; ModuleID = 'foo.3a1fbbbh-cgu.0'
+source_filename = "foo.3a1fbbbh-cgu.0"
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+; Rust source to regenerate:
+; $ cat foo.rs
+; pub struct Foo;
+; impl Foo {
+;     pub fn foo() {}
+; }
+; $ rustc foo.rs --crate-type lib -Cdebuginfo=1 --emit=llvm-ir
+
+; CHECK:      CodeViewTypes [
+; CHECK:        MemberFunction (0x1006) {
+; CHECK-NEXT:     TypeLeafKind: LF_MFUNCTION (0x1009)
+; CHECK-NEXT:     ReturnType: void (0x3)
+; CHECK-NEXT:     ClassType: foo::Foo (0x1000)
+; CHECK-NEXT:     ThisType: 0x0
+; CHECK-NEXT:     CallingConvention: NearC (0x0)
+; CHECK-NEXT:     FunctionOptions [ (0x0)
+; CHECK-NEXT:     ]
+; CHECK-NEXT:     NumParameters: 0
+; CHECK-NEXT:     ArgListType: () (0x1005)
+; CHECK-NEXT:     ThisAdjustment: 0
+; CHECK-NEXT:   }
+; CHECK-NEXT:   MemberFuncId (0x1007) {
+; CHECK-NEXT:     TypeLeafKind: LF_MFUNC_ID (0x1602)
+; CHECK-NEXT:     ClassType: foo::Foo (0x1000)
+; CHECK-NEXT:     FunctionType: void foo::Foo::() (0x1006)
+; CHECK-NEXT:     Name: foo
+; CHECK-NEXT:   }
+; CHECK:      CodeViewDebugInfo [
+; CHECK:        FunctionLineTable [
+; CHECK-NEXT:     LinkageName: _ZN3foo3Foo3foo17hc557c2121772885bE
+; CHECK-NEXT:     Flags: 0x0
+; CHECK-NEXT:     CodeSize: 0x1
+; CHECK-NEXT:     FilenameSegment [
+; CHECK-NEXT:       Filename: D:\rust\foo.rs (0x0)
+; CHECK-NEXT:       +0x0 [
+; CHECK-NEXT:         LineNumberStart: 3
+; CHECK-NEXT:         LineNumberEndDelta: 0
+; CHECK-NEXT:         IsStatement: No
+; CHECK-NEXT:       ]
+; CHECK-NEXT:     ]
+; CHECK-NEXT:   ]
+
+; foo::Foo::foo
+; Function Attrs: uwtable
+define void @_ZN3foo3Foo3foo17hc557c2121772885bE() unnamed_addr #0 !dbg !5 {
+start:
+  ret void, !dbg !10
+}
+
+attributes #0 = { uwtable "target-cpu"="x86-64" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_Rust, file: !1, producer: "clang LLVM (rustc version 1.33.0-nightly (8b0f0156e 2019-01-22))", isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "foo.rs", directory: "D:\5Crust")
+!2 = !{}
+!3 = !{i32 2, !"CodeView", i32 1}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "foo", linkageName: "_ZN3foo3Foo3foo17hc557c2121772885bE", scope: !6, file: !1, line: 3, type: !9, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, templateParams: !2, retainedNodes: !2)
+!6 = !DICompositeType(tag: DW_TAG_structure_type, name: "Foo", scope: !8, file: !7, align: 8, elements: !2, templateParams: !2, identifier: "5105d9fe1a2a3c68518268151b672274")
+!7 = !DIFile(filename: "<unknown>", directory: "")
+!8 = !DINamespace(name: "foo", scope: null)
+!9 = !DISubroutineType(types: !2)
+!10 = !DILocation(line: 3, scope: !5)