Re: [sdcc-devel] [ sdcc-Feature Requests-992518 ] "critical" could do better job

[Maarten B. <sou...@ds...>]

Hi again,

Comments in the middle ;-)
> 
> On Fri, 22 Oct 2004, Maarten Brock wrote:
> 
> > I would like to hear some comments on this from you. I see three 
> > approaches:
> > 1) keep it as it is
> > 2) change according to the request
> > 3) accept "critical" before as well as after the function specifier and 
> > change behaviour accordingly.
> > 
> > Your opinion please?
> > Maarten
> > 
> [Feature request #992518 asks that interrupts are disabled prior to stack
> frame setup rather than after for functions with the "critical" attribute]
> 
> If the syntax of option #3 is implemented (so that the syntax is similar
> to the C standard's handling of the "inline" keyword), I would prefer that
> the alternate syntax not change the behavior. That is, there should only
> be one behavior for "critical" at the function scope.

That is not what I meant, I guess. I meant:
  critical void foo (void) { } /* go critical as early as possible */
  void foo (void) critical { } /* go critical as late as possible */

Otherwise I see no reason to change the language. Or at least there is 
no RFE for it. And I don't like the solution of an extra parameter or 
more keywords either.

> The tricky bit with implementing the request is keeping the stack offsets
> correct. If the psw if pushed before the stack frame is set up, the
> offsets to the parameters will need adjusting. Although aopGet/aopPut
> could compensate for this in the backend, the debugging symbols are
> generated elsewhere and would not reflect the offset change. This was as
> far as I originally pondered the request, since it seemed to need more
> extensive changes than I was comfortable with.
> 
> On a second look, I think I see a fairly simple solution. SDCCast.c's
> createFunction() already handles other cases of discontinuities on the
> stack between a function's parameters and its local variables; we could
> simply add something like:
> 
> if (IFFUNC_ISCRITICAL (name->type))
>   stackPtr -= port->stack.direction * port->stack.critical_overhead;
> 
> with the appropriate additions to port.h, */main.c, and */gen.c (of
> course, the port implementation can set port->stack.critical_overhead to 0
> if this change in behavior is inconvenient or undesired and leave the
> backend code generator alone).
> 
> As far as I can tell, there is no run-time penalty for this change, so I
> would opt to implement as requested.
> 
>   Erik