[Bug c++/88819] New: ICE (segfault) when compiling C++ code with -std=c++2a

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88819

            Bug ID: 88819
           Summary: ICE (segfault) when compiling C++ code with -std=c++2a
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

This appears to be a recent regression.

$ g++tk -v
Using built-in specs.
COLLECT_GCC=g++tk
COLLECT_LTO_WRAPPER=/home/su/software/tmp/gcc/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/9.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/home/su/software/tmp/gcc/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 9.0.0 20190112 (experimental) [trunk revision 267885] (GCC) 
$ 
$ g++tk -std=c++2a tmp.cpp
g++tk: internal compiler error: Segmentation fault signal terminated program
cc1plus
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://gcc.gnu.org/bugs/> for instructions.
$ 


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template < typename T, template < T > class TT, class R = TT < 0 > > struct A 
{
  template < R > struct B {};
};

template < int > struct C {};

A < int, C, C < 0 > > a;