Re: [avr-gcc-list] Feature request - compiler warning for "if" stmtsthat do nothing

[Dave Hansen]

From: Douglas Dotson <address@hidden>

> --- Dave Hansen <address@hidden> wrote:
[...]
> > My preference is something like
> >
> >    while (*dst++ = *src++)
> >       continue;
>
> Won't this generate extra code (an extra jump)? Or
> does the optimizer take it out? My concern is that

No.

I wrote a small test file to check it out:

---begin include file ---
C:\Dave>type continue.c
void copy1(char *dst, const char *src)
{
   while (*dst++ = *src++)
       /*do nothing*/;
}

void copy2(char *dst, const char *src)
{
   while (*dst++ = *src++)
       continue;
}

---end included file---

Compiling with "avr-gcc -S" I get two identical functions 45 instructions 
long.

Compiling with "avr-gcc -S -Os", each function is reduced to 9 instructions, 
but they're still identical.

> using the "continue" kind of obscures the meaning
> of the code. One has to think about the intent rather
> than the ; which is immedeately obvious.

I disagree.  The lone semicolon is small, easily missed, and more likely to 
be the result of a typo.  The continue says "This iteration of the loop is 
complete: continue with the next one."  And as a skeptic, I trust code over 
comments, which is why I prefer it to the "do nothing" comment

It's just about the only place the "continue" statement appears in my code.

Regards,
  -=Dave