[DebugInfo] Handle generic type DW_OP_convert ops in llvm-dwarfdump

[dstenb]

Summary

This is a preparatory change for introducing a new operation that'll let
us emit DW_OP_convert operations converting to the generic type.

If DW_OP_convert's operand is 0, it converts the top of stack to the
generic type, as specified by DWARFv5 section 2.5.1.6:

"[...] takes one operand, which is an unsigned LEB128 integer that
represents the offset of a debugging information entry in the current
compilation unit, or value 0 which represents the generic type."

This adds support for such operations to llvm-dwarfdump.

llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp

bool DWARFExpression::Operation::print(raw_ostream &OS,
   for (unsigned Operand = 0; Operand < 2; ++Operand) {
     unsigned Size = Desc.Op[Operand];
     unsigned Signed = Size & Operation::SignBit;
 
     if (Size == Operation::SizeNA)
       break;
 
     if (Size == Operation::BaseTypeRef && U) {
+      // For DW_OP_convert the operand may be 0 to indicate that conversion to
+      // the generic type should be done. The same holds for DW_OP_reinterpret,
+      // which is currently not supported.
+      if (Opcode == DW_OP_convert && Operands[Operand] == 0)
+        OS << " 0x0";
+      else
         prettyPrintBaseTypeRef(U, OS, Operands, Operand);
     } else if (Size == Operation::SizeBlock) {
       uint64_t Offset = Operands[Operand];
       for (unsigned i = 0; i < Operands[Operand - 1]; ++i)
         OS << format(" 0x%02x", Expr->Data.getU8(&Offset));
     } else {
       if (Signed)
         OS << format(" %+" PRId64, (int64_t)Operands[Operand]);
       else if (Opcode != DW_OP_entry_value &&
bool DWARFExpression::Operation::verify(DWARFUnit *U) {
 
   for (unsigned Operand = 0; Operand < 2; ++Operand) {
     unsigned Size = Desc.Op[Operand];
 
     if (Size == Operation::SizeNA)
       break;
 
     if (Size == Operation::BaseTypeRef) {
+      // For DW_OP_convert the operand may be 0 to indicate that conversion to
+      // the generic type should be done, so don't look up a base type in that
+      // case. The same holds for DW_OP_reinterpret, which is currently not
+      // supported.
+      if (Opcode == DW_OP_convert && Operands[Operand] == 0)
+        continue;
       auto Die = U->getDIEForOffset(U->getOffset() + Operands[Operand]);
       if (!Die || Die.getTag() != dwarf::DW_TAG_base_type) {
         Error = true;
         return false;
       }
     }
   }
 

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

+# RUN: llvm-mc %s -filetype obj -triple x86_64-pc-linux -dwarf-version=5 -o %t.o
+# RUN: llvm-dwarfdump %t.o | FileCheck %s
+# RUN: llvm-dwarfdump -verify %t.o
+
+# CHECK: DW_AT_location  (DW_OP_constu 0x7b, DW_OP_convert 0x0, DW_OP_stack_value)
+
+  .text
+  .file "const.ll"
+  .globl  foo                     # -- Begin function foo
+  .p2align  4, 0x90
+  .type foo,@function
+foo:                                    # @foo
+.Lfoo$local:
+.Lfunc_begin0:
+  .file 0 "/const.c"
+  .loc  0 1 0                   # const.c:1:0
+  .cfi_startproc
+# %bb.0:                                # %entry
+  .loc  0 3 1 prologue_end      # const.c:3:1
+  retq
+.Ltmp0:
+.Lfunc_end0:
+  .size foo, .Lfunc_end0-foo
+  .cfi_endproc
+                                        # -- End function
+  .section  .debug_abbrev,"",@progbits
+  .byte 1                       # Abbreviation Code
+  .byte 17                      # DW_TAG_compile_unit
+  .byte 1                       # DW_CHILDREN_yes
+  .byte 37                      # DW_AT_producer
+  .byte 37                      # DW_FORM_strx1
+  .byte 19                      # DW_AT_language
+  .byte 5                       # DW_FORM_data2
+  .byte 3                       # DW_AT_name
+  .byte 37                      # DW_FORM_strx1
+  .byte 114                     # DW_AT_str_offsets_base
+  .byte 23                      # DW_FORM_sec_offset
+  .byte 16                      # DW_AT_stmt_list
+  .byte 23                      # DW_FORM_sec_offset
+  .byte 27                      # DW_AT_comp_dir
+  .byte 37                      # DW_FORM_strx1
+  .byte 17                      # DW_AT_low_pc
+  .byte 27                      # DW_FORM_addrx
+  .byte 18                      # DW_AT_high_pc
+  .byte 6                       # DW_FORM_data4
+  .byte 115                     # DW_AT_addr_base
+  .byte 23                      # DW_FORM_sec_offset
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 2                       # Abbreviation Code
+  .byte 46                      # DW_TAG_subprogram
+  .byte 1                       # DW_CHILDREN_yes
+  .byte 17                      # DW_AT_low_pc
+  .byte 27                      # DW_FORM_addrx
+  .byte 18                      # DW_AT_high_pc
+  .byte 6                       # DW_FORM_data4
+  .byte 64                      # DW_AT_frame_base
+  .byte 24                      # DW_FORM_exprloc
+  .byte 122                     # DW_AT_call_all_calls
+  .byte 25                      # DW_FORM_flag_present
+  .byte 3                       # DW_AT_name
+  .byte 37                      # DW_FORM_strx1
+  .byte 58                      # DW_AT_decl_file
+  .byte 11                      # DW_FORM_data1
+  .byte 59                      # DW_AT_decl_line
+  .byte 11                      # DW_FORM_data1
+  .byte 63                      # DW_AT_external
+  .byte 25                      # DW_FORM_flag_present
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 3                       # Abbreviation Code
+  .byte 52                      # DW_TAG_variable
+  .byte 0                       # DW_CHILDREN_no
+  .byte 2                       # DW_AT_location
+  .byte 24                      # DW_FORM_exprloc
+  .byte 3                       # DW_AT_name
+  .byte 37                      # DW_FORM_strx1
+  .byte 58                      # DW_AT_decl_file
+  .byte 11                      # DW_FORM_data1
+  .byte 59                      # DW_AT_decl_line
+  .byte 11                      # DW_FORM_data1
+  .byte 73                      # DW_AT_type
+  .byte 19                      # DW_FORM_ref4
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 4                       # Abbreviation Code
+  .byte 36                      # DW_TAG_base_type
+  .byte 0                       # DW_CHILDREN_no
+  .byte 3                       # DW_AT_name
+  .byte 37                      # DW_FORM_strx1
+  .byte 62                      # DW_AT_encoding
+  .byte 11                      # DW_FORM_data1
+  .byte 11                      # DW_AT_byte_size
+  .byte 11                      # DW_FORM_data1
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 0                       # EOM(3)
+  .section  .debug_info,"",@progbits
+.Lcu_begin0:
+  .long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
+.Ldebug_info_start0:
+  .short  5                       # DWARF version number
+  .byte 1                       # DWARF Unit Type
+  .byte 8                       # Address Size (in bytes)
+  .long .debug_abbrev           # Offset Into Abbrev. Section
+  .byte 1                       # Abbrev [1] 0xc:0x36 DW_TAG_compile_unit
+  .byte 0                       # DW_AT_producer
+  .short  12                      # DW_AT_language
+  .byte 1                       # DW_AT_name
+  .long .Lstr_offsets_base0     # DW_AT_str_offsets_base
+  .long .Lline_table_start0     # DW_AT_stmt_list
+  .byte 2                       # DW_AT_comp_dir
+  .byte 0                       # DW_AT_low_pc
+  .long .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
+  .long .Laddr_table_base0      # DW_AT_addr_base
+  .byte 2                       # Abbrev [2] 0x23:0x1a DW_TAG_subprogram
+  .byte 0                       # DW_AT_low_pc
+  .long .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
+  .byte 1                       # DW_AT_frame_base
+  .byte 87
+                                        # DW_AT_call_all_calls
+  .byte 3                       # DW_AT_name
+  .byte 0                       # DW_AT_decl_file
+  .byte 1                       # DW_AT_decl_line
+                                        # DW_AT_external
+  .byte 3                       # Abbrev [3] 0x2e:0xe DW_TAG_variable
+  .byte 5                       # DW_AT_location
+  .byte 16
+  .byte 123
+  .byte 168
+  .byte 0
+  .byte 159
+  .byte 4                       # DW_AT_name
+  .byte 0                       # DW_AT_decl_file
+  .byte 2                       # DW_AT_decl_line
+  .long 61                      # DW_AT_type
+  .byte 0                       # End Of Children Mark
+  .byte 4                       # Abbrev [4] 0x3d:0x4 DW_TAG_base_type
+  .byte 5                       # DW_AT_name
+  .byte 5                       # DW_AT_encoding
+  .byte 4                       # DW_AT_byte_size
+  .byte 0                       # End Of Children Mark
+.Ldebug_info_end0:
+  .section  .debug_str_offsets,"",@progbits
+  .long 28
+  .short  5
+  .short  0
+.Lstr_offsets_base0:
+  .section  .debug_str,"MS",@progbits,1
+.Linfo_string0:
+  .asciz  "clang version 11.0.0"  # string offset=0
+.Linfo_string1:
+  .asciz  "const.c"               # string offset=21
+.Linfo_string2:
+  .asciz  "/"                     # string offset=29
+.Linfo_string3:
+  .asciz  "foo"                   # string offset=31
+.Linfo_string4:
+  .asciz  "local"                 # string offset=35
+.Linfo_string5:
+  .asciz  "int"                   # string offset=41
+  .section  .debug_str_offsets,"",@progbits
+  .long .Linfo_string0
+  .long .Linfo_string1
+  .long .Linfo_string2
+  .long .Linfo_string3
+  .long .Linfo_string4
+  .long .Linfo_string5
+  .section  .debug_addr,"",@progbits
+  .long .Ldebug_addr_end0-.Ldebug_addr_start0 # Length of contribution
+.Ldebug_addr_start0:
+  .short  5                       # DWARF version number
+  .byte 8                       # Address size
+  .byte 0                       # Segment selector size
+.Laddr_table_base0:
+  .quad .Lfunc_begin0
+.Ldebug_addr_end0:
+  .ident  "clang version 11.0.0"
+  .section  ".note.GNU-stack","",@progbits
+  .section  .debug_line,"",@progbits
+.Lline_table_start0: