[llvm-dwarfdump] dump link to the immediate parent.

[avl]

Summary

It is often useful to know which die is the parent of the current die.
This patch adds information about parent offset into the dump:

0x0000000b: DW_TAG_compile_unit
              DW_AT_producer    ("by_hand")

0x00000014:   DW_TAG_base_type (0x0000000b)  <<<<<<<<<<<<<<
                DW_AT_name      ("int")

Now it is easy to see which die is the parent of the current die.
This patch makes that behaviour to be default.
We can make it to be opt-in if neccessary.

This functionality differs from already existed "--show-parents"
in that sence that parent information is shown for all dies and
only link to the immediate parent is shown.

[probinson]

I'd rather see this as part of Verbose. The DIEs are indented to show nesting already, so the explicit parent offset is really additional information.

[avl]

addressed comment(move dumping under Verbose).

[probinson]

LGTM

[jhenderson]

llvm/test/tools/llvm-dwarfdump/X86/parent_link.s

2

Perhaps call the test parent-offset.test or parent-offset.yaml.

1. Underscores are annoying to type - prefer - where possible.
2. This test doesn't contain assembly, so use .test or .yaml instead.
3. offset in the name is more explicit. I might even suggest tag-parent-offset.yaml might be especially clear.

5–8

Personal preference: use ## for comments in new tests, to distinguish the comments from the lit and FileCheck directives.

12

I'd suggest adding one sibling and one additional child tag (child of DW_TAG_base_type or the new sibling), to show the variation in the parent offset.

[avl]

addressed comments(renamed test, added child)

[avl]

addressed comments(renamed test, added child)

[jhenderson]

LGTM.

llvm/lib/DebugInfo/DWARF/DWARFDie.cpp

if (debug_info_data.isValidOffset(offset)) {
     if (abbrCode) {
       auto AbbrevDecl = getAbbreviationDeclarationPtr();
       if (AbbrevDecl) {
         WithColor(OS, HighlightColor::Tag).get().indent(Indent)
             << formatv("{0}", getTag());
         if (DumpOpts.Verbose)
           OS << format(" [%u] %c", abbrCode,
                        AbbrevDecl->hasChildren() ? '*' : ' ');
+        if (Optional<uint32_t> ParentIdx = Die->getParentIdx())
+          OS << format(" (0x%8.8" PRIx64 ")",
+                       U->getDIEAtIndex(*ParentIdx).getOffset());
         OS << '\n';
 
         // Dump all data in the DIE for the attributes.
         for (const DWARFAttribute &AttrValue : attributes())
           dumpAttribute(OS, *this, AttrValue, Indent, DumpOpts);
 
         if (DumpOpts.ShowChildren && DumpOpts.ChildRecurseDepth > 0) {
           DWARFDie Child = getFirstChild();

llvm/test/tools/llvm-dwarfdump/X86/parent_link.s

+# RUN: yaml2obj %s -o %t.o
+# RUN: llvm-dwarfdump -a %t.o | FileCheck %s
+
+# This test checks that llvm-dwarfdump prints link
+# to the parent of the current die:
+
+# DW_TAG_base_type (0x0000000b) <<<<<
+
+# CHECK: .o: file format
+# CHECK: 0x0000000b: DW_TAG_compile_unit
+# CHECK: DW_TAG_base_type (0x0000000b)
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+DWARF:
+  debug_abbrev:
+    - Table:
+      - Tag:      DW_TAG_compile_unit
+        Children: DW_CHILDREN_yes
+        Attributes:
+          - Attribute: DW_AT_producer
+            Form:      DW_FORM_string
+      - Tag:      DW_TAG_base_type
+        Children: DW_CHILDREN_no
+        Attributes:
+          - Attribute: DW_AT_name
+            Form:      DW_FORM_string
+  debug_info:
+    - Version: 4
+      Entries:
+        - AbbrCode: 1
+          Values:
+            - CStr: by_hand
+        - AbbrCode: 2
+          Values:
+            - CStr: int

llvm/test/tools/llvm-dwarfdump/X86/verbose.test

 # RUN: llvm-mc %S/brief.s -filetype obj -triple x86_64-apple-darwin -o %t.o
 # RUN: llvm-dwarfdump -v --debug-info --debug-line %t.o | \
 # RUN:   FileCheck %s --match-full-lines --strict-whitespace
 
 #   CHECK-NOT:{{.*}} contents:
 
 #       CHECK:.debug_info contents:
 #       CHECK:0x0000000b: DW_TAG_compile_unit [1] *
 #       CHECK:              DW_AT_name [DW_FORM_strp] ( .debug_str[0x{{.*}}] = "brief.c")
-#       CHECK:0x0000002a:   DW_TAG_subprogram [2]  
+#       CHECK:0x0000002a:   DW_TAG_subprogram [2]   (0x0000000b)
 #       CHECK:                DW_AT_name [DW_FORM_strp] ( .debug_str[0x{{.*}}] = "main")
-#       CHECK:0x00000043:   DW_TAG_base_type [3]  
+#       CHECK:0x00000043:   DW_TAG_base_type [3]   (0x0000000b)
 #  CHECK-NEXT:                DW_AT_name [DW_FORM_strp] ( .debug_str[0x{{.*}}] = "int")
 
 #       CHECK:.debug_line contents:
 #       CHECK:         length: 0x00000000
 # CHECK-EMPTY:
 #  CHECK-NEXT:            Address            Line   Column File   ISA Discriminator Flags
 #  CHECK-NEXT:            ------------------ ------ ------ ------ --- ------------- -------------
 #  CHECK-NEXT:0x00000029: 00 DW_LNE_set_address (0x0000000000000000)