[Bug c++/94210] New: ICE in tsubst, at cp/pt.c:15105

[tangyixuan at mail dot dlut.edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94210

            Bug ID: 94210
           Summary: ICE in tsubst, at cp/pt.c:15105
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tangyixuan at mail dot dlut.edu.cn
  Target Milestone: ---

Hi, gcc crashes given the following example, while clang compiles normally.
$ cat 1.cpp
template<typename ...T> struct X {};

namespace Nested {
  template<typename ...T> int f1(X<T, T...>... a);

  int a1 = f1(X<int, int, double>(), X<double, int, double>());
}

$ g++ -v
Using built-in specs.
COLLECT_GCC=/usr/local/gcc-20200315/bin/g++
COLLECT_LTO_WRAPPER=/usr/local/gcc-20200315/libexec/gcc/x86_64-pc-linux-gnu/10.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-10-20200315/configure --prefix=/usr/local/gcc-20200315
--enable-checking=release --enable-languages=c,c++ --disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.0.1 20200315 (experimental) (GCC) 

$　g++ -c -std=c++11 1.cpp

1.cpp: In substitution of ‘template<class ... T> int Nested::f1(X<T, T ...>...)
[with T = <missing>]’:
1.cpp:6:62:   required from here
1.cpp:6:62: internal compiler error: in tsubst, at cp/pt.c:15105
    6 |   int a1 = f1(X<int, int, double>(), X<double, int, double>());
      |                                                              ^
0x5f0f06 tsubst(tree_node*, tree_node*, int, tree_node*)
        ../../gcc-10-20200315/gcc/cp/pt.c:15105
0x75dd9a unify_pack_expansion
        ../../gcc-10-20200315/gcc/cp/pt.c:22534
0x74aff5 unify
        ../../gcc-10-20200315/gcc/cp/pt.c:23307
0x74a20a unify
        ../../gcc-10-20200315/gcc/cp/pt.c:23204
0x74ae8b unify
        ../../gcc-10-20200315/gcc/cp/pt.c:23301
0x75e5da try_class_unification
        ../../gcc-10-20200315/gcc/cp/pt.c:22298
0x74a744 unify
        ../../gcc-10-20200315/gcc/cp/pt.c:23338
0x75d248 unify_one_argument
        ../../gcc-10-20200315/gcc/cp/pt.c:21531
0x75db29 unify_pack_expansion
        ../../gcc-10-20200315/gcc/cp/pt.c:22546
0x749b80 type_unification_real
        ../../gcc-10-20200315/gcc/cp/pt.c:21670
0x769684 fn_type_unification(tree_node*, tree_node*, tree_node*, tree_node*
const*, unsigned int, tree_node*, unification_kind_t, int, conversion**, bool,
bool)
        ../../gcc-10-20200315/gcc/cp/pt.c:21030
0x640da5 add_template_candidate_real
        ../../gcc-10-20200315/gcc/cp/call.c:3396
0x6414f4 add_template_candidate
        ../../gcc-10-20200315/gcc/cp/call.c:3481
0x6414f4 add_candidates
        ../../gcc-10-20200315/gcc/cp/call.c:5834
0x6418f7 add_candidates
        ../../gcc-10-20200315/gcc/cp/call.c:4482
0x6418f7 perform_overload_resolution
        ../../gcc-10-20200315/gcc/cp/call.c:4490
0x644525 build_new_function_call(tree_node*, vec<tree_node*, va_gc,
vl_embed>**, int)
        ../../gcc-10-20200315/gcc/cp/call.c:4564
0x77bd5c finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool,
bool, int)
        ../../gcc-10-20200315/gcc/cp/semantics.c:2671
0x71f998 cp_parser_postfix_expression
        ../../gcc-10-20200315/gcc/cp/parser.c:7427
0x7041ba cp_parser_binary_expression
        ../../gcc-10-20200315/gcc/cp/parser.c:9519
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.