[DebugInfo] Add parser for DILabel metadata.

[HsiangKai]

Summary

Define DILabel fields for parsing. Call GET_OR_DISTINCT() to create DILabel
objects and store the objects into LLVMContext.

[chenwj]

Nit.

lib/AsmParser/LLParser.cpp

4569

Redundant comment?

[probinson]

Needs a test. Probably should be combined with the Verifier patch as well.

[HsiangKai]

In D45025#1053392, @probinson wrote:

Needs a test. Probably should be combined with the Verifier patch as well.

Merged into D45024, this patch should be abandoned.

lib/AsmParser/LLParser.cpp

 #undef VISIT_MD_FIELDS
 
   Result = GET_OR_DISTINCT(DILocalVariable,
                            (Context, scope.Val, name.Val, file.Val, line.Val,
                             type.Val, arg.Val, flags.Val, align.Val));
   return false;
 }
 
+/// ParseDILabel:
+///   ::= !DILabel(scope: !0, name: "foo", file: !1, line: 7)
+///   ::= !DILabel(scope: !0, name: "foo", file: !1, line: 7)
+bool LLParser::ParseDILabel(MDNode *&Result, bool IsDistinct) {
+#define VISIT_MD_FIELDS(OPTIONAL, REQUIRED)                                    \
+  REQUIRED(scope, MDField, (/* AllowNull */ false));                           \
+  REQUIRED(name, MDStringField, );                                             \
+  REQUIRED(file, MDField, );                                                   \
+  REQUIRED(line, LineField, );
+  PARSE_MD_FIELDS();
+#undef VISIT_MD_FIELDS
+
+  Result = GET_OR_DISTINCT(DILabel,
+                           (Context, scope.Val, name.Val, file.Val, line.Val));
+  return false;
+}
+
 /// ParseDIExpression:
 ///   ::= !DIExpression(0, 7, -1)
 bool LLParser::ParseDIExpression(MDNode *&Result, bool IsDistinct) {
   assert(Lex.getKind() == lltok::MetadataVar && "Expected metadata type name");
   Lex.Lex();
 
   if (ParseToken(lltok::lparen, "expected '(' here"))
     return true;