[llvm] [DebugInfo] Add expression decoding for `DW_OP_implicit_pointer` (PR #102923)

[Felipe de Azevedo Piovezan via llvm-commits]

================
@@ -0,0 +1,87 @@
+# Test that we can decode `DW_OP_implicit_pointer` (0xa0)
+# RUN: yaml2obj %s | llvm-dwarfdump - | FileCheck %s
+
+# CHECK:      DW_TAG_variable
+# CHECK-NEXT:   DW_AT_location (DW_OP_implicit_pointer 0x2a +0)
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+DWARF:
+  debug_abbrev:
+    - Table:
+        - Code:            0x00000001
+          Tag:             DW_TAG_compile_unit
+          Children:        DW_CHILDREN_yes
+          Attributes:
+            - Attribute:       DW_AT_language
+              Form:            DW_FORM_data2
+            - Attribute:       DW_AT_low_pc
+              Form:            DW_FORM_addr
+            - Attribute:       DW_AT_high_pc
+              Form:            DW_FORM_data4
+        - Code:            0x00000002
+          Tag:             DW_TAG_subprogram
+          Children:        DW_CHILDREN_yes
+          Attributes:
+            - Attribute:       DW_AT_low_pc
+              Form:            DW_FORM_addr
+            - Attribute:       DW_AT_high_pc
+              Form:            DW_FORM_data4
+            - Attribute:       DW_AT_frame_base
+              Form:            DW_FORM_exprloc
+        - Code:            0x00000003
+          Tag:             DW_TAG_formal_parameter
+          Children:        DW_CHILDREN_no
+          Attributes:
+            - Attribute:       DW_AT_location
+              Form:            DW_FORM_exprloc
+        - Code:            0x00000004
+          Tag:             DW_TAG_variable
+          Children:        DW_CHILDREN_no
+          Attributes:
+            - Attribute:       DW_AT_location
+              Form:            DW_FORM_exprloc
+  debug_info:
+    - Length:          52
+      Version:         5
+      UnitType:        DW_UT_compile
+      AbbrOffset:      0
+      AddrSize:        8
+      Entries:
+        - AbbrCode:        0x00000001
+          Values:
+            - Value:           0x000000000000000C
+            - Value:           0x0000000100000F50
+            - Value:           0x0000000000000034
+        - AbbrCode:        0x00000002
+          Values:
+            - Value:           0x0000000100000F50
+            - Value:           0x0000000000000034
+            - Value:           0x0000000000000001
+              BlockData:
+                - 0x56
+        - AbbrCode:        0x00000003
+          Values:
+            - Value:           0x0000000000000002
+              BlockData:
+                - 0x91
+                - 0x78
+        - AbbrCode:        0x00000004
+          Values:
+            - Value:           0x0000000000000006
+              BlockData:
+                - 0xa0
+                - 0x2a
----------------
felipepiovezan wrote:

Could you add two comments here, one saying that 0xa0 is the encoding of `DW_OP_implicit_pointer ` and that `0x2a` is the DIE offset for the TAG_variable DIE entry "above" (the one with abbrev code 3)?
Just to make the test slightly easier to reason about

https://github.com/llvm/llvm-project/pull/102923