Re: Bad optimisations: (Was: Test version zsh-3.1.6-test-1)

[Sven Wischnowsky <wischnow@xxxxxxxxxxxxxxxxxxxxxxx>]

mason@xxxxxxxxxxxxxxx wrote:

> Sven Wischnowsky <wischnow@xxxxxxxxxxxxxxxxxxxxxxx> typed:
> :Geoff Wing wrote:
> :> What about just expanding it slightly (with appropriate comments of course)
> :> instead of duplicating it.
> :> e.g.
> :>     if (*args && **args == '?')
> :>         args++;
> :>     /* default result parameter */
> :>     if (*args)
> :>         reply = *args++;
> :>     else
> :>         reply = ops['A'] ? "reply" : "REPLY";
> :Note this isn't intended as an optimisation (of course), but to work
> :around a bug in gcc-2.8.1 under DU.
> 
> I thought it may be a gcc optimisation bug.  i.e. Does it appear at -O0 or
> -01 or -O2?  All of them?

Yes, it is. The problem is in the first two lines of the code
above. If there is only the `args++' in the `then'-branch, `args'
contains a random value after the `if'. This happens with all
optimisation levels, so I guess it's a register allocation problem in
the backend.

Bye
 Sven


--
Sven Wischnowsky                         wischnow@xxxxxxxxxxxxxxxxxxxxxxx