Re: msp430 port

[Jeff Law <law at redhat dot com>]

On 08/19/2013 02:49 PM, DJ Delorie wrote:
> > I'd say it's not as simple as you make it out to be.  You can't blindly
> > combine operations on volatile memory.
>
> I'm not blindly combining them, I'm combining them when I know the
> hardware will do the volatile-correct thing.
You're missing the point.  If the programmer wrote two statements which 
hit volatile memory and you've got some pattern which matches those two 
statements, then with your change you'll end up combining them, that's 
wrong.

> > ie, the programmer may have written them as separate statements and
> > if they're volatile you should leave them alone.
>
> Most of the programmers I know would expect "port |= 0x80;" to do a
> hardware-specific "set bits" operation, not a series of
> volatile-pedantic operations, especially when the ISA has a set of
> insns specifically designed to do bit operations on volatile I/O
> registers.
I fully understand that.  But that doesn't change the fact that if the 
programmer wrote separate statements with volatile operands you can't 
combine them.  Your change allows such combinations as far as I can tell.

You simply don't have enough context at any point to know if what you're 
doing is safe or not.


Jeff