[Bug c++/68509] New: [6 regression][C++1z] ICE: in check_return_expr, at cp/typeck.c:8635

["lucdanton at free dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68509

            Bug ID: 68509
           Summary: [6 regression][C++1z] ICE: in check_return_expr, at
                    cp/typeck.c:8635
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lucdanton at free dot fr
  Target Milestone: ---

Testcase compiles fine in C++11 and C++14 modes, ICE is in C++1z mode only.

$ g++-trunk --version
g++-trunk (GCC) 6.0.0 20151124 (experimental)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ cat main.cpp
constexpr auto foo(int i)
{
    if(i == 0) {
        return 0;
    } else {
        return 'a';
    }
}

int main()
{
    using X = decltype( foo(0) );
    return X {};
}
$ g++-trunk -std=c++1z main.cpp
main.cpp: In function 'constexpr auto foo(int)':
main.cpp:6:16: internal compiler error: in check_return_expr, at
cp/typeck.c:8635
         return 'a';
                ^~~

0x66f5b3 check_return_expr(tree_node*, bool*)
        ../../gcc/gcc/cp/typeck.c:8635
0x68fa5e finish_return_stmt(tree_node*)
        ../../gcc/gcc/cp/semantics.c:867
0x6584e8 cp_parser_jump_statement
        ../../gcc/gcc/cp/parser.c:11414
0x6584e8 cp_parser_statement
        ../../gcc/gcc/cp/parser.c:10035
0x658bac cp_parser_statement_seq_opt
        ../../gcc/gcc/cp/parser.c:10426
0x658ce6 cp_parser_compound_statement
        ../../gcc/gcc/cp/parser.c:10380
0x65fb0c cp_parser_implicitly_scoped_statement
        ../../gcc/gcc/cp/parser.c:11520
0x658a01 cp_parser_selection_statement
        ../../gcc/gcc/cp/parser.c:10555
0x658a01 cp_parser_statement
        ../../gcc/gcc/cp/parser.c:10010
0x658bac cp_parser_statement_seq_opt
        ../../gcc/gcc/cp/parser.c:10426
0x658ce6 cp_parser_compound_statement
        ../../gcc/gcc/cp/parser.c:10380
0x658e3b cp_parser_function_body
        ../../gcc/gcc/cp/parser.c:20192
0x658e3b cp_parser_ctor_initializer_opt_and_function_body
        ../../gcc/gcc/cp/parser.c:20228
0x6599e8 cp_parser_function_definition_after_declarator
        ../../gcc/gcc/cp/parser.c:24836
0x65a93f cp_parser_function_definition_from_specifiers_and_declarator
        ../../gcc/gcc/cp/parser.c:24748
0x65a93f cp_parser_init_declarator
        ../../gcc/gcc/cp/parser.c:17972
0x65ac3d cp_parser_simple_declaration
        ../../gcc/gcc/cp/parser.c:11980
0x65b0d3 cp_parser_block_declaration
        ../../gcc/gcc/cp/parser.c:11854
0x662d35 cp_parser_declaration
        ../../gcc/gcc/cp/parser.c:11751
0x661328 cp_parser_declaration_seq_opt
        ../../gcc/gcc/cp/parser.c:11630
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