On Wednesday 25 April 2007 17:17, Ian Lance Taylor wrote:
> Marco Manfredini <mldb@xxxxxxx> writes:
> Unfortunately a const pointer in C/C++ doesn't mean "the value this
> points to can not change." It only means "the value this points to
> can not be changed via this pointer." So there is no way to express
> what you want in the standard language. Nor does gcc provide an
> extension along these lines.
I hoped there was an __attribute__((const)) for function parameters somewhere
in the hide.
>
> gcc does provide the extension of annotating fun with __attribute__
> ((pure)). If fun is indeed a pure function, then gcc might be perform
> the optimization you want. I haven't tried. Of course, if fun is not
> pure, that won't help.
pure doesn't help, yes. It isn't even available for my x86_64 target. What I
thought of was some clever hack which tricks the compiler into thinking that
a completely new pointer had appeared. I've tried:
const val* __attribute__((malloc)) summon_pointer(const val *p) { return p; }
but with no luck.
If the task is to create a new pointer for which the compiler can't see the
relation to the original, then __asm__ abuse would be my next idea, but I
don't have a clue how to twiddle the constraints for this case.
Marco
