[Bug tree-optimization/71761] missing tailcall optimization

[vanyacpp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71761

--- Comment #2 from Ivan Sorokin <vanyacpp at gmail dot com> ---
I compared this with clang.

1) typedef int token;
Both GCC and clang optimize this to a single jump.

2) struct token {int a};
clang optimizes this into a single jump. GCC generates:
        subq    $8, %rsp
        call    f()
        addq    $8, %rsp
        ret

3) struct token as in the issue
Both compilers do
        pushq   %rbx
        movq    %rdi, %rbx
        call    f()
        movq    %rbx, %rax
        popq    %rbx
        ret

I don't quite understand why both clang and GCC generate different code all
these cases.