[Bug c++/100507] New: ICE on invalid: tree check expects tree that contains 'decl common'

[sand at rifkin dot dev via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100507

            Bug ID: 100507
           Summary: ICE on invalid: tree check expects tree that contains
                    'decl common'
           Product: gcc
           Version: 10.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sand at rifkin dot dev
  Target Milestone: ---

template<decltype(r) n>
void f(auto r){}

Causes an ICE on gcc trunk (11.1 errors correctly):
https://godbolt.org/z/fYe7E9ocM