[PATCH] D104937: [Coroutines] Define __coro_frame_ty in function scope

[David Blaikie via Phabricator via llvm-commits]

dblaikie added a comment.

In D104937#2845409 <https://reviews.llvm.org/D104937#2845409>, @hoy wrote:

> In D104937#2845235 <https://reviews.llvm.org/D104937#2845235>, @dblaikie wrote:
>
>>> We were seeing a type defined in a local scope causing trouble to the dwarf emitter where a context is required to be a funciton scope, a namespace or a global scope.
>>
>> Could you describe this in more detail? It's possible there's a bug somewhere there that should be fixed instead of avoiding that situation?
>
> We have encountered an assert failure at the following line, i.e, the `getOrCreateContextDIE` call. 
> https://github.com/llvm/llvm-project/blob/main/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp#L619
>
> Looking into that function (https://github.com/llvm/llvm-project/blob/main/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp#L538) , I'm not seeing a local scope is supposed to have a DIE created for it. I guess that's by design and dwarf spec.

If by local scopes you mean DILexicalBlock/DW_TAG_lexical_block, those do get DIEs:

  $ cat > scope.cpp
  int main() {
    int i = 3;
    {
      int j = 7;
      {
        int k = 42;
      }
    }
  }
  blaikie at blaikie-linux2:~/dev/scratch$ clang++-tot scope.cpp -g -c && llvm-dwarfdump-tot scope.o
  scope.o:        file format elf64-x86-64
  
  .debug_info contents:
  0x00000000: Compile Unit: length = 0x0000008e, format = DWARF32, version = 0x0004, abbr_offset = 0x0000, addr_size = 0x08 (next unit at 0x00000092)
  
  0x0000000b: DW_TAG_compile_unit
                DW_AT_producer    ("clang version 13.0.0 (git at github.com:llvm/llvm-project.git 9aa951e80e72decd95c7d972e1e0dde24260d336)")
                DW_AT_language    (DW_LANG_C_plus_plus_14)
                DW_AT_name        ("scope.cpp")
                DW_AT_stmt_list   (0x00000000)
                DW_AT_comp_dir    ("/usr/local/google/home/blaikie/dev/scratch")
                DW_AT_low_pc      (0x0000000000000000)
                DW_AT_high_pc     (0x000000000000001d)
  
  0x0000002a:   DW_TAG_subprogram
                  DW_AT_low_pc    (0x0000000000000000)
                  DW_AT_high_pc   (0x000000000000001d)
                  DW_AT_frame_base        (DW_OP_reg6 RBP)
                  DW_AT_name      ("main")
                  DW_AT_decl_file ("/usr/local/google/home/blaikie/dev/scratch/scope.cpp")
                  DW_AT_decl_line (1)
                  DW_AT_type      (0x0000008a "int")
                  DW_AT_external  (true)
  
  0x00000043:     DW_TAG_variable
                    DW_AT_location        (DW_OP_fbreg -4)
                    DW_AT_name    ("i")
                    DW_AT_decl_file       ("/usr/local/google/home/blaikie/dev/scratch/scope.cpp")
                    DW_AT_decl_line       (2)
                    DW_AT_type    (0x0000008a "int")
  
  0x00000051:     DW_TAG_lexical_block
                    DW_AT_low_pc  (0x000000000000000b)
                    DW_AT_high_pc (0x0000000000000019)
  
  0x0000005e:       DW_TAG_variable
                      DW_AT_location      (DW_OP_fbreg -8)
                      DW_AT_name  ("j")
                      DW_AT_decl_file     ("/usr/local/google/home/blaikie/dev/scratch/scope.cpp")
                      DW_AT_decl_line     (4)
                      DW_AT_type  (0x0000008a "int")
  
  0x0000006c:       DW_TAG_lexical_block
                      DW_AT_low_pc        (0x0000000000000012)
                      DW_AT_high_pc       (0x0000000000000019)
  
  0x00000079:         DW_TAG_variable
                        DW_AT_location    (DW_OP_fbreg -12)
                        DW_AT_name        ("k")
                        DW_AT_decl_file   ("/usr/local/google/home/blaikie/dev/scratch/scope.cpp")
                        DW_AT_decl_line   (6)
                        DW_AT_type        (0x0000008a "int")
  
  0x00000087:         NULL
  
  0x00000088:       NULL
  
  0x00000089:     NULL
  
  0x0000008a:   DW_TAG_base_type
                  DW_AT_name      ("int")
                  DW_AT_encoding  (DW_ATE_signed)
                  DW_AT_byte_size (0x04)
  
  0x00000091:   NULL

But if I recall correctly the path to create them is a bit different, because they're created more dynamically, based on the instructions and DebugLocs on those instructions.

But, yes, for local types and local static variables I don't think we currently track their lexical scope info (eg: if you put a named struct in one of the `{}` in the above example it still appears at the top level of the function and in the LLVM IR the `DICompositeType`'s `scope` member points to the `DISubprogram`) - so, yeah, this is a long-standing limitation/bug/etc. Glad to understand this is another case of that. Thanks for the details!


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