Debug Info: Support for DW_AT_export_symbols for anonymous structs

This implements the DWARF 5 feature described in:

http://dwarfstd.org/ShowIssue.php?issue=141212.1

To support recognizing anonymous structs:

  struct A {
    struct { // Anonymous struct
        int y;
    };
  }   a;

This patch adds a new (DI)flag to LLVM metadata:

ExportSymbols

Differential Revision: https://reviews.llvm.org/D66352

llvm-svn: 369781

Author: shafik

llvm/docs/LangRef.rst

@@ -4834,6 +4834,11 @@ after the function prologue. The language frontend is expected to compute
 this property for each DILocalVariable. The flag should be used
 only in optimized code.
 
+The `ExportSymbols` flag marks a class, struct or union whose members
+may be referenced as if they were defined in the containing class or
+union. This flag is used to decide whether the DW_AT_export_symbols can
+be used for the structure type.
+
 DIObjCProperty
 """"""""""""""
 

llvm/include/llvm/IR/DebugInfoFlags.def

@@ -42,8 +42,7 @@ HANDLE_DI_FLAG((1 << 11), Vector)
 HANDLE_DI_FLAG((1 << 12), StaticMember)
 HANDLE_DI_FLAG((1 << 13), LValueReference)
 HANDLE_DI_FLAG((1 << 14), RValueReference)
-// 15 was formerly ExternalTypeRef, but this was never used.
-HANDLE_DI_FLAG((1 << 15), Reserved)
+HANDLE_DI_FLAG((1 << 15), ExportSymbols)
 HANDLE_DI_FLAG((1 << 16), SingleInheritance)
 HANDLE_DI_FLAG((2 << 16), MultipleInheritance)
 HANDLE_DI_FLAG((3 << 16), VirtualInheritance)

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -668,6 +668,7 @@ class DIType : public DIScope {
   }
   bool isBigEndian() const { return getFlags() & FlagBigEndian; }
   bool isLittleEndian() const { return getFlags() & FlagLittleEndian; }
+  bool getExportSymbols() const { return getFlags() & FlagExportSymbols; }
 
   static bool classof(const Metadata *MD) {
     switch (MD->getMetadataID()) {

llvm/test/Assembler/export-symbol-anonymous-class.ll

@@ -0,0 +1,38 @@
+; Round trip for the following:
+; ```
+; struct A {
+;  struct {
+;      int y;
+;  };
+; } a;
+; ```
+; This is the minimum code to generate export symbols flag due to anonymous class in A.
+
+; RUN: llvm-as %s -o - | llvm-dis | llvm-as | llvm-dis | FileCheck %s
+
+%struct.A = type { %struct.anon }
+%struct.anon = type { i32 }
+
+@a = global %struct.A zeroinitializer, align 4, !dbg !0
+
+!llvm.module.flags = !{!14, !15}
+!llvm.dbg.cu = !{!2}
+!llvm.ident = !{!16}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "a", scope: !2, file: !3, line: 5, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 10.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: GNU)
+!3 = !DIFile(filename: "simple_anon_class.cpp", directory: "/dir")
+!4 = !{}
+!5 = !{!0}
+!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "A", file: !3, line: 1, size: 32, flags: DIFlagTypePassByValue, elements: !7, identifier: "_ZTS1A")
+!7 = !{!8}
+!8 = !DIDerivedType(tag: DW_TAG_member, scope: !6, file: !3, line: 2, baseType: !9, size: 32)
+!9 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !6, file: !3, line: 2, size: 32, flags: DIFlagExportSymbols | DIFlagTypePassByValue, elements: !10, identifier: "_ZTSN1AUt_E")
+; CHECK: DIFlagExportSymbols | DIFlagTypePassByValue
+!10 = !{!11}
+!11 = !DIDerivedType(tag: DW_TAG_member, name: "y", scope: !9, file: !3, line: 3, baseType: !12, size: 32)
+!12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !{i32 2, !"Dwarf Version", i32 4}
+!15 = !{i32 2, !"Debug Info Version", i32 3}
+!16 = !{!"clang version 10.0.0"}