[clang] static constexpr variable initialized inside consteval function is loosing its value

[hanickadot]

Any variable initialized as static constexpr variable inside consteval is not keeping its value in runtime:

consteval const int & get_value() {
    constexpr static int value = 42;
    return value;
}

int foo() {
  return get_value();
}

generates assembly (with clang 18.1):

foo():                                # @foo()
        push    rbp
        mov     rbp, rsp
        mov     eax, dword ptr [rip + get_value()::value]
        pop     rbp
        ret
get_value()::value:
        .long   0    

confirmed with clang 16+ to current main branch (597ac471cc7da97ccf957362a7e9f7a52d6910ee at compiler explorer)

link to example: https://compiler-explorer.com/z/fj6zco3d5

same thing happens to strings and arrays ... their storage is all zeros

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Hana Dusíková (hanickadot)

Any variable initialized as `static constexpr` variable inside `consteval` is not keeping its value in runtime:

consteval const int & get_value() {
    constexpr static int value = 42;
    return value;
}

int foo() {
  return get_value();
}

generates assembly (with clang 18.1):

foo():                                # @<!-- -->foo()
        push    rbp
        mov     rbp, rsp
        mov     eax, dword ptr [rip + get_value()::value]
        pop     rbp
        ret
get_value()::value:
        .long   0    

confirmed with clang 16+ to current main branch (597ac471cc7da97ccf957362a7e9f7a52d6910ee at compiler explorer)

link to example: https://compiler-explorer.com/z/fj6zco3d5

same thing happens to strings and arrays ... their storage is all zeros

[hanickadot]

A little bit better example: https://compiler-explorer.com/z/vTE8WYMGz

[shafik]

I believe this is a duplicate of: #82994

Using constexpr causes the problem to go away: https://compiler-explorer.com/z/hTaTTGsv9

CC @cor3ntin @Fznamznon

[hanickadot]

Yes, you are correct, this seem as the same problem.