■

Shift 演算の最適化弱いなあ GCC。

jun@debian /tmp
$ cat tmp.c
int
f (int x)
{
        return (x & ~1) >> 2;
}
jun@debian /tmp
$ gcc -S -o - -O2 tmp.c
        .file   "tmp.c"
        .text
        .p2align 4,,15
.globl f
        .type   f, @function
f:
        pushl   %ebp
        movl    %esp, %ebp
        movl    8(%ebp), %eax
        popl    %ebp
        andl    $-2, %eax
        sarl    $2, %eax
        ret
        .size   f, .-f
        .ident  "GCC: (GNU) 4.0.3 (Debian 4.0.3-1)"
        .section        .note.GNU-stack,"",@progbits