[Bug middle-end/110459] Trivial on stack variable was not optimized away

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110459

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually the problem is not what is listed in comment #2 at all but rather
the expansion of
;; MEM <char[3]> [(struct array *)&buffer + 1B] = {};

Being so bad.
```
(insn 6 5 7 (set (mem/c:HI (plus:DI (reg/f:DI 93 virtual-stack-vars)
                (const_int -16 [0xfffffffffffffff0])) [0  S2 A128])
        (const_int 0 [0])) "/app/example.cpp":7:9 -1
     (nil))

(insn 7 6 9 (set (mem/c:QI (plus:DI (reg/f:DI 93 virtual-stack-vars)
                (const_int -14 [0xfffffffffffffff2])) [0  S1 A16])
        (const_int 0 [0])) "/app/example.cpp":7:9 -1
     (nil))

(insn 9 7 10 (set (reg:SI 105)
        (mem/c:SI (plus:DI (reg/f:DI 93 virtual-stack-vars)
                (const_int -16 [0xfffffffffffffff0])) [0  S4 A128]))
"/app/example.cpp":7:9 -1
     (nil))

(insn 10 9 11 (parallel [
            (set (reg:SI 104)
                (and:SI (reg:SI 105)
                    (const_int 16777215 [0xffffff])))
            (clobber (reg:CC 17 flags))
        ]) "/app/example.cpp":7:9 -1
     (expr_list:REG_EQUAL (and:SI (mem/c:SI (plus:DI (reg/f:DI 93
virtual-stack-vars)
                    (const_int -16 [0xfffffffffffffff0])) [0  S4 A128])
            (const_int 16777215 [0xffffff]))
        (nil)))

(insn 11 10 12 (parallel [
            (set (reg:SI 106)
                (ashift:SI (reg:SI 104)
                    (const_int 8 [0x8])))
            (clobber (reg:CC 17 flags))
        ]) "/app/example.cpp":7:9 -1
     (nil))

(insn 12 11 13 (set (reg:SI 107)
        (zero_extend:SI (subreg:QI (reg/v:SI 99 [ bufferD.3003 ]) 0)))
"/app/example.cpp":7:9 -1
     (nil))

(insn 13 12 14 (parallel [
            (set (reg:SI 108)
                (ior:SI (reg:SI 107)
                    (reg:SI 106)))
            (clobber (reg:CC 17 flags))
        ]) "/app/example.cpp":7:9 -1
     (nil))

(insn 14 13 0 (set (reg/v:SI 99 [ bufferD.3003 ])
        (reg:SI 108)) "/app/example.cpp":7:9 -1
     (nil))
```

Note:
```
auto sample2(char c) {
  array buffer = {0, 0, 0, 0};
  buffer.data[0] = c;
  return buffer;
}
```
is just as bad:
movl    .LC0(%rip), %eax
movb    %dil, %al

LC0 is just 0s.