[Bug rtl-optimization/113185] New: bad performance on big-endian&64bit port for struct 16 16

["syq at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113185

            Bug ID: 113185
           Summary: bad performance on big-endian&64bit port for struct 16
                    16
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: syq at gcc dot gnu.org
  Target Milestone: ---

```
struct xx {
        int a:16;
        int b:16;
};

struct xx xx (struct xx a, long long b) {
        a.b = b;
        return a;
}
```

On little-endian&64, only 1 or 2 instructions are used, such as
on AARCH64el:

```
        bfi     w0, w1, 16, 16
        ret
```
On MIPS64el
```
        move    $2,$4
        sll     $5,$5,0
        jr      $31
        ins     $2,$5,16,16
```


While for 64EB
```
        .cfi_startproc
        sub     sp, sp, #16
        .cfi_def_cfa_offset 16
        str     x0, [sp, 8]
        strh    w1, [sp, 10]
        ldr     w0, [sp, 8]
        add     sp, sp, 16
        .cfi_def_cfa_offset 0
        lsl     x0, x0, 32
        ret
        .cfi_endproc
```
```
        daddiu  $sp,$sp,-16
        sd      $4,0($sp)
        sh      $5,2($sp)
        lw      $2,0($sp)
        daddiu  $sp,$sp,16
        jr      $31
        dsll    $2,$2,32
```