http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46973
Summary: DW_TAG_structure_type can loose its
DW_TAG_template{type,value}_param et al children
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: do...@gcc.gnu.org
Consider this attachment: http://gcc.gnu.org/bugzilla/attachment.cgi?id=21610
The resulting DWARF yields good results for Base<double, ...>:
<1><47>: Abbrev Number: 5 (DW_TAG_structure_type)
<48> DW_AT_name : (indirect string, offset: 0x43): Base<double,
23, (& a_global), &S::f>
<4c> DW_AT_byte_size : 1
<4d> DW_AT_decl_file : 1
<4e> DW_AT_decl_line : 29
<4f> DW_AT_sibling : <0xb4>
<2><53>: Abbrev Number: 6 (DW_TAG_template_type_param)
<54> DW_AT_name : T
<56> DW_AT_type : <0xb4>
[...]
But for Base<long, ...>, not so much. It is missing all the template parameters
and arguments:
<1><d0>: Abbrev Number: 5 (DW_TAG_structure_type)
<d1> DW_AT_name : (indirect string, offset: 0x191): Base<long int,
47, (& a_global), &S::f>
<d5> DW_AT_byte_size : 1
<d6> DW_AT_decl_file : 1
<d7> DW_AT_decl_line : 29
<d8> DW_AT_sibling : <0x105>
<2><dc>: Abbrev Number: 16 (DW_TAG_structure_type)
<dd> DW_AT_name : (indirect string, offset: 0x157): Inner<float>
<e1> DW_AT_byte_size : 1
<e2> DW_AT_decl_file : 1
<e3> DW_AT_decl_line : 32
<3><e4>: Abbrev Number: 6 (DW_TAG_template_type_param)
<e5> DW_AT_name : Z
<e7> DW_AT_type : <0x10c>
<3><eb>: Abbrev Number: 12 (DW_TAG_subprogram)
<ec> DW_AT_external : 1
<ed> DW_AT_name : (indirect string, offset: 0xa8): inner_m
<f1> DW_AT_decl_file : 1
<f2> DW_AT_decl_line : 34
<f3> DW_AT_MIPS_linkage_name: (indirect string, offset: 0xb0):
_ZN4BaseIlLi47EXadL_Z8a_globalEEXadL_ZN1S1fEEEE5InnerIfE7inner_mEv
<f7> DW_AT_declaration : 1
<f8> DW_AT_object_pointer: <0xfc>
<4><fc>: Abbrev Number: 11 (DW_TAG_formal_parameter)
<fd> DW_AT_type : <0x113>
<101> DW_AT_artificial : 1
This has been filed as a comment for bug debug/41736, but I am creating this PR
instead as the bug is slightly different.
Here is what I think is happening. The template parms/args children DIEs of the
DW_TAG_structure_type of Base<long int, 47, (& a_global), &S::f> are not
marked [and that's the bug] as being used so they are not emitted.
The type Base<long, 47, &a_global, &S::f> itself is not used directly. The type
that is used is Base<long, 47, &a_global, &S::f>::Inner<float>.
So prune_unused_types_mark marks the DIE of Base<long, 47, &a_global,
&S::f>::Inner<float> as being used; it also marks the parent DIE as used. That
is, it marks the DW_TAG_structure_type DIE of Base<long, 47, &a_global, &S::f>
as being used. But it marks that DW_TAG_structure_type DIE *only* (along with
its attributes. Not its children DIEs -- so it forgets to mark the
DW_TAG_template{type,value}_param children DIEs as well.
I think the purpose of marking the parent DIE of the DW_TAG_structure_type of
Base<long, 47, &a_global, &S::f>::Inner<float> as used is just to define the
names space it belongs to. So it is generally fine to avoid emitting the
children DIEs of that parent DIE -- unless some of those children DIEs
participate in defining the name space Base<long, 47, &a_global,
&S::f>::Inner<float> belongs to. And we are in this corner case here.
I believe this depends on PR debug/46955 because once we stop forgetting the
DW_TAG_template_value DIEs, we must properly emit its DW_AT_const_value
attribute.
