[Bug lto/113208] [14 Regression] lto1: error: Alias and target's comdat groups differs since r14-5979-g99d114c15523e0

["hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113208

--- Comment #25 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
So we have comdat groups that diverges in t1.o and t2.o.  In one object it has
alias in it while in other object it does not

Merging nodes for _ZN6vectorI12QualityValueEC2ERKS1_. Candidates:
_ZN6vectorI12QualityValueEC2ERKS1_/1 (__ct_base )
  Type: function definition analyzed
  Visibility: externally_visible semantic_interposition prevailing_def_ironly
public weak comdat comdat_group:_ZN6vectorI12QualityValueEC2ERKS1_ one_only
  next sharing asm name: 19
  References: 
  Referring:  
  Read from file: t1.o
  Unit id: 1
  Function flags: count:1073741824 (estimated locally)
  Called by: _Z1n1k/6 (1073741824 (estimated locally),1.00 per call) (can throw
external)
  Calls: _ZN12_Vector_baseI12QualityValueEC2Eii/10 (1073741824 (estimated
locally),1.00 per call) (can throw external)
_ZNK12_Vector_baseI12QualityValueE1gEv/9 (1073741824 (estimated locally),1.00
per call) (can throw external)
_ZN6vectorI12QualityValueEC2ERKS1_/19 (__ct_base )
  Type: function definition analyzed
  Visibility: externally_visible semantic_interposition preempted_ir public
weak comdat comdat_group:_ZN6vectorI12QualityValueEC5ERKS1_ one_only
  Same comdat group as: _ZN6vectorI12QualityValueEC1ERKS1_/20
  previous sharing asm name: 1
  References: 
  Referring: _ZN6vectorI12QualityValueEC1ERKS1_/20 (alias)
  Read from file: t2.o
  Unit id: 2
  Function flags: count:1073741824 (estimated locally)
  Called by:
  Calls: _ZN12_Vector_baseI12QualityValueEC2Eii/23 (1073741824 (estimated
locally),1.00 per call) (can throw external)
_ZNK12_Vector_baseI12QualityValueE1gEv/24 (1073741824 (estimated locally),1.00
per call) (can throw external)
After resolution:
_ZN6vectorI12QualityValueEC2ERKS1_/1 (__ct_base )
  Type: function definition analyzed
  Visibility: externally_visible semantic_interposition prevailing_def_ironly
public weak comdat comdat_group:_ZN6vectorI12QualityValueEC2ERKS1_ one_only
  next sharing asm name: 19
  References: 
  Referring: 
  Read from file: t1.o
  Unit id: 1
  Function flags: count:1073741824 (estimated locally)
  Called by: _Z1n1k/6 (1073741824 (estimated locally),1.00 per call) (can throw
external)
  Calls: _ZN12_Vector_baseI12QualityValueEC2Eii/10 (1073741824 (estimated
locally),1.00 per call) (can throw external)
_ZNK12_Vector_baseI12QualityValueE1gEv/9 (1073741824 (estimated locally),1.00
per call) (can throw external)

We opt for version without alias and later ICE in sanity check verifying that
aliases have same comdat group as their targets.

I wonder how this is ice-on-valid code, since with normal linking the aliased
symbol may or may not appear in the winning comdat group, so using he alias has
to break.

If constexpr changes how the constructor is generated, isn't this violation of
ODR?

We probably can go and reset every node in losing comdat group to silence the
ICE and getting undefined symbol instead