[Bug default/25450] Compress member function template DIEs

[Bug default/25450] Compress member function template DIEs

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=25450

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #0)
> Despite the fact that the two DIEs are generated from the same header file,
> they are structurally different, due to the different instantiations of the
> member function template. Consequently, dwz does not factor out the DIEs.

One way to address this is to generate the union of the DIEs into a partial
unit.    [ This does create the problem of having references from that union to
DIEs that are unique to a certain CU, and consequently don't have a duplicate
chain. ]

Another way is to factor out the common part of the DIEs into a partial unit,
and include it from the original DIEs using DW_AT_specification.

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[Bug default/25450] New: Compress member function template DIEs

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=25450

            Bug ID: 25450
           Summary: Compress member function template DIEs
           Product: dwz
           Version: unspecified
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: default
          Assignee: nobody at sourceware dot org
          Reporter: vries at gcc dot gnu.org
                CC: dwz at sourceware dot org
  Target Milestone: ---

Consider the following test-case.

test.h:
...
struct aaa
{
  template<typename T> void foo(T obj) {}
};
...

test.cc:
...
extern void other_unit (void);

#include "test.h"

struct aaa var;

int
main (void)
{
  int a;
  float f;
  var.foo (a);
  var.foo (f);
  other_unit ();
  return 0;
}
...

test2.cc:
...
#include "test.h"

struct aaa var2;

void
other_unit (void)
{
  double d;
  var2.foo (d);
}
...

Compiled like this:
...
$ g++ test.cc test2.cc -g
...

In the test.cc compilation unit, we have:
...
 <1><f0>: Abbrev Number: 2 (DW_TAG_structure_type)
    <f1>   DW_AT_name        : aaa
    <f5>   DW_AT_byte_size   : 1
    <f6>   DW_AT_decl_file   : 2
    <f7>   DW_AT_decl_line   : 1
    <f8>   DW_AT_sibling     : <0x143>
 <2><fc>: Abbrev Number: 3 (DW_TAG_subprogram)
    <fd>   DW_AT_external    : 1
    <fd>   DW_AT_name        : (indirect string, offset: 0x1d0): foo<float>
    <101>   DW_AT_decl_file   : 2
    <102>   DW_AT_decl_line   : 3
    <103>   DW_AT_linkage_name: (indirect string, offset: 0x262):
_ZN3aaa3fooIfEEvT_
    <107>   DW_AT_declaration : 1
    <107>   DW_AT_object_pointer: <0x116>
    <10b>   DW_AT_sibling     : <0x121>
 <3><10f>: Abbrev Number: 4 (DW_TAG_template_type_param)
    <110>   DW_AT_name        : T
    <112>   DW_AT_type        : <0x158>
 <3><116>: Abbrev Number: 5 (DW_TAG_formal_parameter)
    <117>   DW_AT_type        : <0x15f>
    <11b>   DW_AT_artificial  : 1
 <3><11b>: Abbrev Number: 6 (DW_TAG_formal_parameter)
    <11c>   DW_AT_type        : <0x158>
 <3><120>: Abbrev Number: 0
 <2><121>: Abbrev Number: 7 (DW_TAG_subprogram)
    <122>   DW_AT_external    : 1
    <122>   DW_AT_name        : (indirect string, offset: 0x254): foo<int>
    <126>   DW_AT_decl_file   : 2
    <127>   DW_AT_decl_line   : 3
    <128>   DW_AT_linkage_name: (indirect string, offset: 0x1db):
_ZN3aaa3fooIiEEvT_
    <12c>   DW_AT_declaration : 1
    <12c>   DW_AT_object_pointer: <0x137>
 <3><130>: Abbrev Number: 4 (DW_TAG_template_type_param)
    <131>   DW_AT_name        : T
    <133>   DW_AT_type        : <0x1af>
 <3><137>: Abbrev Number: 5 (DW_TAG_formal_parameter)
    <138>   DW_AT_type        : <0x15f>
    <13c>   DW_AT_artificial  : 1
 <3><13c>: Abbrev Number: 6 (DW_TAG_formal_parameter)
    <13d>   DW_AT_type        : <0x1af>
...

And in the test2.cc compilation unit, we have:
...
 <1><25b>: Abbrev Number: 2 (DW_TAG_structure_type)
    <25c>   DW_AT_name        : aaa
    <260>   DW_AT_byte_size   : 1
    <261>   DW_AT_decl_file   : 2
    <262>   DW_AT_decl_line   : 1
    <263>   DW_AT_sibling     : <0x289>
 <2><267>: Abbrev Number: 3 (DW_TAG_subprogram)
    <268>   DW_AT_external    : 1
    <268>   DW_AT_name        : (indirect string, offset: 0x2b7): foo<double>
    <26c>   DW_AT_decl_file   : 2
    <26d>   DW_AT_decl_line   : 3
    <26e>   DW_AT_linkage_name: (indirect string, offset: 0x27b):
_ZN3aaa3fooIdEEvT_
    <272>   DW_AT_declaration : 1
    <272>   DW_AT_object_pointer: <0x27d>
 <3><276>: Abbrev Number: 4 (DW_TAG_template_type_param)
    <277>   DW_AT_name        : T
    <279>   DW_AT_type        : <0x29e>
 <3><27d>: Abbrev Number: 5 (DW_TAG_formal_parameter)
    <27e>   DW_AT_type        : <0x2a5>
    <282>   DW_AT_artificial  : 1
 <3><282>: Abbrev Number: 6 (DW_TAG_formal_parameter)
    <283>   DW_AT_type        : <0x29e>
...

Despite the fact that the two DIEs are generated from the same header file,
they are structurally different, due to the different instantiations of the
member function template. Consequently, dwz does not factor out the DIEs.

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