[DWARFYAML] Abbrev codes in a new abbrev table should start from 1 (by default).

[Higuoxing]

Summary

The abbrev codes in a new abbrev table should start from 1 (by default),
rather than inherit the value from the code in the previous table.

[jhenderson]

LGTM!

llvm/lib/ObjectYAML/DWARFEmitter.cpp

for (auto Str : DI.DebugStrings) {
     OS.write(Str.data(), Str.size());
     OS.write('\0');
   }
 
   return Error::success();
 }
 
 Error DWARFYAML::emitDebugAbbrev(raw_ostream &OS, const DWARFYAML::Data &DI) {
-  uint64_t AbbrevCode = 0;
   for (const DWARFYAML::AbbrevTable &AbbrevTable : DI.DebugAbbrev) {
+    uint64_t AbbrevCode = 0;
     for (const DWARFYAML::Abbrev &AbbrevDecl : AbbrevTable.Table) {
       AbbrevCode =
           AbbrevDecl.Code ? (uint64_t)*AbbrevDecl.Code : AbbrevCode + 1;
       encodeULEB128(AbbrevCode, OS);
       encodeULEB128(AbbrevDecl.Tag, OS);
       OS.write(AbbrevDecl.Children);
       for (auto Attr : AbbrevDecl.Attributes) {
         encodeULEB128(Attr.Attribute, OS);

llvm/test/tools/yaml2obj/ELF/DWARF/debug-abbrev.yaml

 # RUN: llvm-readelf --hex-dump=.debug_abbrev %t8.o | FileCheck %s --check-prefix=CODE
 
 #      CODE: 0x00000000 01110000 00022e00 0000042e 00000004
 ##                      ^-                                  abbreviation code ULEB128
 ##                                 ^-                       abbreviation code ULEB128
 ##                                            ^-            abbreviation code (ULEB128) 0x04
 ##                                                       ^- abbreviation code (ULEB128) 0x04
 ##
-# CODE-NEXT: 0x00000010 2e000000 052e0000 00062e00 0000
-##                               ^-                     abbreviation code ULEB128
-##                                          ^-          abbreviation code ULEB128
+# CODE-NEXT: 0x00000010 2e000000 052e0000 00062e00 00000001
+##                               ^-                         abbreviation code ULEB128
+##                                          ^-              abbreviation code ULEB128
+##                                                       ^- abbreviation code ULEB128
+# CODE-NEXT: 0x00000020 11000000 022e0000 0000
+##                               ^-                         abbreviation code ULEB128
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_EXEC
 DWARF:
   debug_abbrev:
     - Table:
         - Tag:        DW_TAG_compile_unit
           Children:   DW_CHILDREN_no
         - Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
         - Code:       4
           Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
         - Code:       4
           Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
         - Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
         - Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
+    - Table:
+        ## Test that the abbrev codes in a new table start from 1 by default.
+        - Tag:        DW_TAG_compile_unit
+          Children:   DW_CHILDREN_no
+        - Tag:        DW_TAG_subprogram
+          Children:   DW_CHILDREN_no
 
 ## i) Test that yaml2obj emits an error message when there are non-empty compilation units
 ## and multiple abbrev tables are assigned the same ID.
 
 ## RUN: not yaml2obj --docnum=9 %s 2>&1 | FileCheck %s --check-prefix=ID-COLLISION
 
 # ID-COLLISION: yaml2obj: error: the ID (1) of abbrev table with index 1 has been used by abbrev table with index 0