[Bug c/111786] New: No tail recursion for simple program

["lukas.graetz@tu-darmstadt.de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111786

            Bug ID: 111786
           Summary: No tail recursion for simple program
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lukas.graetz@tu-darmstadt.de
  Target Milestone: ---

Created attachment 56096
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56096&action=edit
C code of expr_main

Follow up with nearly the same source file as 111643, only without the flatten
attribute. Sorry for taking so long for that. I learned the optimized compiler
should output a tail recursion. But this seams not to be the case: With "sub"
and "call", 16 bytes on the stack are used.

The file attached file contains:

---
int expr_main(int argc, char **argv)
{
    return expr_main_original(argc, argv);
}
---

And after cc1 -O3 on amd64, the output contains:

-- gcc 13.2.0 --
expr_main:
        subq    $8, %rsp
        call    expr_main_original
---

-- gcc 9.4.0 shipped with ubuntu 20.04 ---
expr_main:
        endbr64
        pushq   %rax
        popq    %rax
        pushq   %rax
        call    expr_main_original
---

-- Expected --
expr_main:
        jmp     expr_main_original
---

If I compile the above snippet only, I get the expected result. But not when
compiling the whole C file which also includes the body of
expr_main_original(). I also suspect there are some other factors I don't know,
since many other functions I tested yield the expected result.

In my case, the overhead seams to be negligible. However, I think it should be
possible to construct similar recursive programs where the overhead compared to
tail recursion is not negligible.