[Bug target/124171] bpf: procedure calling convention ABI incompatible with clang (argument/return value promotion)

[vineetg at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124171

--- Comment #2 from Vineet Gupta <vineetg at gcc dot gnu.org> ---
While the changes above fix the argument promotion in caller, it seems to
regress the return value promotion in caller (which was already happening, but
not anymore for some cases).

_Bool bar_bool(void);
int foo_bool_ne1(void) {
      if (bar_bool() != 1) return 0; else return 1;
}

-O2

W/ patch (NOK)         |   w/o patch (OK)
                       |
foo_bool_ne1:          | foo_bool_ne1:   
   call    bar_bool    |   call    bar_bool
   exit                |   r0 &= 0xff
                       |   exit    

Weirdly this works for char, and even for bool case above with != 0

_Bool bar_bool(void);
int foo_bool_ne0(void) {
      if (bar_bool() != 0) return 0; else return 1;
}

foo_bool_ne0:
        call    bar_bool
        w0 ^= 1
        r0 &= 0xff
        exit

Currently debugging this.