Re: Strange warning message

[reinert <reinkor@gmail.com>]

On Monday, November 27, 2017 at 11:42:11 AM UTC+1, Jeffrey R. Carter wrote:
> On 11/27/2017 09:40 AM, reinert wrote:
> > 
> > when I compile the enclosed program with option "-gnatwa" (i.e. "gnatmake -gnatwa test1k.adb", I get the following annoying warning:
> > 
> > "warning: useless assignment to "test1", value never referenced"
> 
> In order to produce warnings like this, the compiler has to do some data-flow 
> analysis. The amount of data-flow analysis required by the ARM is zero. So GNAT 
> is making an extra effort to be helpful. That the warning is annoying in this 
> case is the price you pay for it being correct in most others.
> 
> Clearly GNAT's data-flow analysis is incomplete, or it would also flag the 
> assignment in the loop. Complete data-flow analysis is possible (SPARK does it). 
> but apparently it's hard, and possibly not really compatible with a compiler's 
> main purpose, but even if GNAT did have complete data-flow analysis, you'd still 
> get the warning.
> 
> I found that even if I change the loop to
> 
> for I in Test1'range loop
>     Test1 (I) := new Test1_T;
> end loop;
> 
> GNAT (7.2) still doesn't flag the assignment in the loop, so it's not just that 
> GNAT's analysis hasn't caught up with the new "for E of" construct.
> 
> -- 
> Jeff Carter
> "We burst our pimples at you."
> Monty Python & the Holy Grail
> 16

This clarifies, reinert