Re: Request of new __attribute__ for switch statements (eliminationof the bounds check)

[Ralph Loader <suckfish at ihug dot co dot nz>]

A more general feature would be a __builtin_not_reached() that informs
the compiler that a particular code path will never be executed and can
be removed at compile time.

Then the example below could be achieved by adding 

   default: __builtin_not_reached();

to the switch statement.

Ralph.

On Sat, 2002-10-12 at 08:05, Kevin Lawton wrote:
> All,
> 
> For implementation of machine simulators, it's quite common
> to have completely populated switch statements on byte values:
> 
>   unsigned char byte;
> 
>   switch (byte) {
>     case 0:
>     case 1:
>     ...
>     case 255:
>     }
> 
> But I don't know of any way to tell the compiler to _not_ generate
> a bounds check on the switch variable 'byte'.  All of the target
> space is covered.
> 
> To solve this, could we add an attribute to switch?
> 
>   switch (byte) __attribute (( no-bounds-check )) {
>     ...
>     }
> 
> This would also be useful for cases, where it is known that
> all possible targets are covered with case statements, yet
> they don't appear to be fully populated to the compiler
> (it's known only to the programmer that the logic prevents
> certain values).
> 
> Thanks,
> -Kevin
> 
> __________________________________________________
> Do you Yahoo!?
> New DSL Internet Access from SBC & Yahoo!
> http://sbc.yahoo.com
>