[DWARFYAML] Make the 'Attributes' field optional.

[Higuoxing]

Summary

This patch makes the 'Attributes' field optional. We don't need to
explicitly specify the 'Attributes' field in the future.

[grimar]

LGTM

[jhenderson]

LGTM too.

llvm/lib/ObjectYAML/DWARFYAML.cpp

void MappingTraits<DWARFYAML::AbbrevTable>::mapping(
   IO.mapOptional("Table", AbbrevTable.Table);
 }
 
 void MappingTraits<DWARFYAML::Abbrev>::mapping(IO &IO,
                                                DWARFYAML::Abbrev &Abbrev) {
   IO.mapOptional("Code", Abbrev.Code);
   IO.mapRequired("Tag", Abbrev.Tag);
   IO.mapRequired("Children", Abbrev.Children);
-  IO.mapRequired("Attributes", Abbrev.Attributes);
+  IO.mapOptional("Attributes", Abbrev.Attributes);
 }
 
 void MappingTraits<DWARFYAML::AttributeAbbrev>::mapping(
     IO &IO, DWARFYAML::AttributeAbbrev &AttAbbrev) {
   IO.mapRequired("Attribute", AttAbbrev.Attribute);
   IO.mapRequired("Form", AttAbbrev.Form);
   if(AttAbbrev.Form == dwarf::DW_FORM_implicit_const)
     IO.mapRequired("Value", AttAbbrev.Value);

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

 ## Test that yaml2obj emits .debug_abbrev section.
 
 ## a) Generate the .debug_abbrev section from the "DWARF" entry.
 
 # RUN: yaml2obj --docnum=1 %s -o %t1.o
 # RUN: llvm-readobj --sections --section-data %t1.o | \
-# RUN:   FileCheck -DSIZE=54 -DADDRALIGN=1 %s --check-prefixes=SHDR,CONTENT
+# RUN:   FileCheck -DSIZE=59 -DADDRALIGN=1 %s --check-prefixes=SHDR,CONTENT
 
 #         SHDR: Index: 1
 #    SHDR-NEXT: Name: .debug_abbrev (1)
 #    SHDR-NEXT: Type: SHT_PROGBITS (0x1)
 #    SHDR-NEXT: Flags [ (0x0)
 #    SHDR-NEXT: ]
 #    SHDR-NEXT: Address: 0x0
 #    SHDR-NEXT: Offset: 0x40

 ##                      ^------- Value SLEB128 (12345678)           ^---     attr terminator
 ##                                                                      ^-   abbrev terminator
 ##                                                                        ^- abbreviation code ULEB128
 #      CONTENT:         1101250E                                    0000022E |..........%.....|
 ##                      ^-       DW_TAG_compile_unit ULEB128        ^---     attr terminator
 ##                        ^-     DW_CHILDREN_yes     1-byte             ^-   abbreviation code ULEB128
 ##                          ^-   DW_AT_producer      ULEB128              ^- DW_TAG_subprogram ULEB128
 ##                            ^- DW_FORM_strp        ULEB128
-# CONTENT-NEXT:   0030: 01110100 0000 |......|
-##                      ^-            DW_CHILDREN_yes 1-byte
-##                        ^-          DW_AT_low_pc    ULEB128
-##                          ^-        DW_FORM_addr    UELB128
-##                            ^----   attr terminator
-##                                 ^- abbrev table terminator
+# CONTENT-NEXT:   0030: 01110100 00031100                           000000   |...........|
+##                      ^-                DW_CHILDREN_yes 1-byte    ^---     attr terminator
+##                        ^-              DW_AT_low_pc    ULEB128       ^-   abbrev table terminator
+##                          ^-            DW_FORM_addr    UELB128
+##                            ^----       attr terminator
+##                                 ^-     abbrev code ULEB128 (0x03)
+##                                   ^-   DW_TAG_compile_unit
+##                                     ^- DW_CHILDREN_no
 # CONTENT-NEXT: )
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_EXEC
 DWARF:
- Table:
             - Attribute: DW_AT_producer
               Form:      DW_FORM_strp
         - Code:     2
           Tag:      DW_TAG_subprogram
           Children: DW_CHILDREN_yes
           Attributes:
             - Attribute: DW_AT_low_pc
               Form:      DW_FORM_addr
+        ## Test that if the 'Attributes' field is not specified, yaml2obj emits
+        ## a terminating entry, 0 for the attribute, 0 for the form.
+        - Tag:      DW_TAG_compile_unit
+          Children: DW_CHILDREN_no
 
 ## b) Generate the .debug_abbrev section from raw section content.
 
 # RUN: yaml2obj --docnum=2 %s -o %t2.o
 # RUN: llvm-readobj --sections --section-data %t2.o | \
 # RUN:   FileCheck -DADDRALIGN=0 -DSIZE=3 %s --check-prefixes=SHDR,ARBITRARY-CONTENT
 
 # ARBITRARY-CONTENT-NEXT: SectionData (
- Name: .debug_abbrev
     Type: SHT_PROGBITS
     Size: 0x10
 DWARF:
   debug_abbrev:
     - Table:
         - Code:       1
           Tag:        DW_TAG_compile_unit
           Children:   DW_CHILDREN_no
-          Attributes: []
 
 ## e) Test that yaml2obj emits an error message when both the "Content" and the
 ## "debug_abbrev" entry are specified at the same time.
 
 # RUN: not yaml2obj --docnum=5 %s 2>&1 | FileCheck %s --check-prefix=ERROR
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_EXEC
 Sections:
   - Name:    .debug_abbrev
     Type:    SHT_PROGBITS
     Content: "00"
 DWARF:
   debug_abbrev:
     - Table:
         - Code:       1
           Tag:        DW_TAG_compile_unit
           Children:   DW_CHILDREN_no
-          Attributes: []
 
 ## f) Test that all the properties can be overridden by the section header when
 ## the "debug_abbrev" entry doesn't exist.
 
 # RUN: yaml2obj --docnum=6 %s -o %t6.o
 # RUN: llvm-readelf --sections %t6.o | FileCheck %s --check-prefix=OVERRIDDEN
 
 #      OVERRIDDEN: [Nr] Name          Type   Address          Off    Size   ES Flg Lk Inf Al
Sections:
   - Name:         .sec        ## Linked by .debug_abbrev.
     Type:         SHT_STRTAB
 DWARF:
   debug_abbrev:
     - Table:
         - Code:       1
           Tag:        DW_TAG_compile_unit
           Children:   DW_CHILDREN_no
-          Attributes: []
 
 ## h) Test that yaml2obj automatically generates abbreviation codes for us.
 
 # RUN: yaml2obj --docnum=8 %s -o %t8.o
 # RUN: llvm-readelf --hex-dump=.debug_abbrev %t8.o | FileCheck %s --check-prefix=CODE
 
 #      CODE: 0x00000000 01110000 00022e00 0000042e 00000004
 ##                      ^-                                  abbreviation code ULEB128
FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_EXEC
 DWARF:
   debug_abbrev:
     - Table:
         - Tag:        DW_TAG_compile_unit
           Children:   DW_CHILDREN_no
-          Attributes: []
         - Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
-          Attributes: []
         - Code:       4
           Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
-          Attributes: []
         - Code:       4
           Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
-          Attributes: []
         - Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
-          Attributes: []
         - Tag:        DW_TAG_subprogram
           Children:   DW_CHILDREN_no
-          Attributes: []
 
 ## 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
 

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

- Name: .debug_info
     Type: SHT_PROGBITS
     Size: 0x10
 DWARF:
   debug_abbrev:
     - Table:
         - Code:       1
           Tag:        DW_TAG_compile_unit
           Children:   DW_CHILDREN_no
-          Attributes: []
   debug_info:
     - Length:     0x1234
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
       Entries:    []
 
 ## e) Test that yaml2obj emits an error message when both the "Content" and the
- Name: .debug_info
     Type: SHT_PROGBITS
     Content: "00"
 DWARF:
   debug_abbrev:
     - Table:
         - Code:       1
           Tag:        DW_TAG_compile_unit
           Children:   DW_CHILDREN_no
-          Attributes: []
   debug_info:
     - Length:     0x1234
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
       Entries:    []
 
 ## f) Test that all the properties can be overridden by the section header when
Sections:
   - Name:         .sec        ## Linked by .debug_info.
     Type:         SHT_STRTAB
 DWARF:
   debug_abbrev:
     - Table:
         - Code:       1
           Tag:        DW_TAG_compile_unit
           Children:   DW_CHILDREN_no
-          Attributes: []
   debug_info:
     - Length:     0x1234
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
       Entries:
         - AbbrCode: 0
           Values:   []

llvm/unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp

 }
 
 TEST(DWARFDebugInfo, TestEmptyChildren) {
   const char *yamldata = "debug_abbrev:\n"
                          "  - Table:\n"
                          "      - Code:            0x00000001\n"
                          "        Tag:             DW_TAG_compile_unit\n"
                          "        Children:        DW_CHILDREN_yes\n"
-                         "        Attributes:\n"
                          "debug_info:\n"
                          "  - Version:         4\n"
                          "    AbbrOffset:      0\n"
                          "    AddrSize:        8\n"
                          "    Entries:\n"
                          "      - AbbrCode:        0x00000001\n"
                          "        Values:\n"
                          "      - AbbrCode:        0x00000000\n"