[Bug c++/71459] New: ICE writing to a string-initialized local array in a constexpr function

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71459

            Bug ID: 71459
           Summary: ICE writing to a string-initialized local array in a
                    constexpr function
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

All versions of GCC that support C++ 14 constexpr functions fail with an ICE on
the following valid test case.

$ cat cst.C && /home/msebor/build/gcc-trunk-svn/gcc/xgcc -B
/home/msebor/build/gcc-trunk-svn/gcc -Wall -Wextra -Wpedantic -xc++ cst.C
constexpr int f ()
{
  char a [] = "ab";
  a [1] = 'c';
  return 0; 
}

constexpr int i = f ();
cst.C: In function ‘constexpr int f()’:
cst.C:3:8: warning: variable ‘a’ set but not used [-Wunused-but-set-variable]
   char a [] = "ab";
        ^
cst.C: At global scope:
cst.C:8:21:   in constexpr expansion of ‘f()’
cst.C:8:22: internal compiler error: tree check: expected constructor, have
string_cst in cxx_eval_store_expression, at cp/constexpr.c:3072
 constexpr int i = f ();
                      ^
0x140cc34 tree_check_failed(tree_node const*, char const*, int, char const*,
...)
        /src/gcc-svn/gcc/tree.c:9752
0x792c15 tree_check(tree_node*, char const*, int, char const*, tree_code)
        /src/gcc-svn/gcc/tree.h:3030
0xa6f784 cxx_eval_store_expression
        /src/gcc-svn/gcc/cp/constexpr.c:3072
0xa71ccc cxx_eval_constant_expression
        /src/gcc-svn/gcc/cp/constexpr.c:3656
0xa727df cxx_eval_constant_expression
        /src/gcc-svn/gcc/cp/constexpr.c:3927
0xa71f2e cxx_eval_constant_expression
        /src/gcc-svn/gcc/cp/constexpr.c:3697
0xa71f2e cxx_eval_constant_expression
        /src/gcc-svn/gcc/cp/constexpr.c:3697
0xa7073a cxx_eval_statement_list
        /src/gcc-svn/gcc/cp/constexpr.c:3352
0xa72e5e cxx_eval_constant_expression
        /src/gcc-svn/gcc/cp/constexpr.c:3983
0xa72edd cxx_eval_constant_expression
        /src/gcc-svn/gcc/cp/constexpr.c:3989
0xa6957c cxx_eval_call_expression
        /src/gcc-svn/gcc/cp/constexpr.c:1500
0xa714db cxx_eval_constant_expression
        /src/gcc-svn/gcc/cp/constexpr.c:3579
0xa737ca cxx_eval_outermost_constant_expr
        /src/gcc-svn/gcc/cp/constexpr.c:4157
0xa73e63 cxx_constant_value(tree_node*, tree_node*)
        /src/gcc-svn/gcc/cp/constexpr.c:4255
0x88c6e8 store_init_value(tree_node*, tree_node*, vec<tree_node*, va_gc,
vl_embed>**, int)
        /src/gcc-svn/gcc/cp/typeck2.c:816
0x7d80de check_initializer
        /src/gcc-svn/gcc/cp/decl.c:6172
0x7db1f2 cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int)
        /src/gcc-svn/gcc/cp/decl.c:6827
0x915ea7 cp_parser_init_declarator
        /src/gcc-svn/gcc/cp/parser.c:18697
0x90b184 cp_parser_simple_declaration
        /src/gcc-svn/gcc/cp/parser.c:12378
0x90af45 cp_parser_block_declaration
        /src/gcc-svn/gcc/cp/parser.c:12246
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