volatile

[Doug Gwyn]

In article <390 at attila.weitek.UUCP> mahar at attila.UUCP (Mike Mahar) writes:
>char fifo;
>buf_fill(buffer,cnt)
>    char *buffer;
>    int cnt;
>    {
>    int i;
>    for( i = 0; i < cnt; i++)
>	*buffer++ = fifo;
	^ MISSING * ADDED
>    }
>Question: Is it safe to compile the preceding routine like this:
>	movb	_fifo,d2	#pre-load fifo
>L1:

In this particular case it is safe to pre-load `fifo' before the loop.
(It would be disallowed if `fifo' were declared "volatile".)  However,
if the code were changed to

char fifo[3];
buf_fill(buffer,cnt)
    char *buffer;
    int cnt;
    {
    int i;
    for( i = 0; i < cnt; i++)
	*buffer++ = fifo[1];
    }

Then it would NOT be permitted to pre-load fifo[0],
because the function could be invoked as

	buf_fill(fifo,3);

and the generated code must handle the aliasing correctly.