[Bug middle-end/91526] Unnecessary SSE and other instructions generated when compiling in C mode (vs. C++ mode)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91526

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The difference between GCC 12 and 13 is:

GCC 12:
```
;; <retval> = result;

(insn 12 11 13 (set (reg:TI 91)
        (mem/c:TI (plus:DI (reg/f:DI 77 virtual-stack-vars)
                (const_int -32 [0xffffffffffffffe0])) [2 resultD.2491+0 S16
A256])) "/app/example.cpp":8:12 -1
     (nil))

(insn 13 12 14 (set (mem/c:TI (reg/f:DI 85 [ .result_ptrD.2520 ]) [2 <retval>+0
S16 A32])
        (reg:TI 91)) "/app/example.cpp":8:12 -1
     (nil))

(insn 14 13 15 (set (reg:TI 92)
        (mem/c:TI (plus:DI (reg/f:DI 77 virtual-stack-vars)
                (const_int -16 [0xfffffffffffffff0])) [2 resultD.2491+16 S16
A128])) "/app/example.cpp":8:12 -1
     (nil))

(insn 15 14 0 (set (mem/c:TI (plus:DI (reg/f:DI 85 [ .result_ptrD.2520 ])
                (const_int 16 [0x10])) [2 <retval>+16 S16 A32])
        (reg:TI 92)) "/app/example.cpp":8:12 -1
     (nil))
```


vs:
GCC 13:
```
(insn 12 11 13 (set (reg:OI 91)
        (mem/c:OI (plus:DI (reg/f:DI 77 virtual-stack-vars)
                (const_int -32 [0xffffffffffffffe0])) [2 resultD.3251+0 S32
A256])) "/app/example.cpp":8:12 -1
     (nil))

(insn 13 12 0 (set (mem/c:OI (reg/f:DI 85 [ .result_ptrD.3280 ]) [2 <retval>+0
S32 A32])
        (reg:OI 91)) "/app/example.cpp":8:12 -1
     (nil))
```

Looks like how the copy was done into the return location.