[Fortran,patch] PR 41850 - Wrong-code with optional allocatable arrays

[Daniel Kraft]

Tobias Burnus wrote:
> The first part is obvious: if the actual argument to an optional
> allocatable dummy is in turn an optional dummy and it is not present,
> then one needs to guard the access with "if(present(...))".
> 
> The second part removes unnecessary code. Currently, one generates:
> 
>     D.555 = a != 0B ? a : 0B;
>     sub2 (D.555);
> 
> which is identical to passing "a" directly. As additional variables make
> the alias analysis, the -O0 code side and the reading of the dump
> harder, I removed it. For scalar arguments to elemental functions one
> still has unnecessarily
>     integer(kind=4) * D.1388;
>     D.1388 = ivec;
>     [...]
>             set_optional (&ivec_[S.6], &D.1390, D.1388);
> while for array arguments to elementals the IF is needed:
>             D.1415 = ivec != 0B ? &(*ivec.0)[(S.10 + 1) * D.1413 +
> D.1408] : 0B;
>             set_optional (&ivec_[S.10], &D.1414, D.1415);
> In some cases, the argument needs always to resolve to a valid pointer
> of value 1 or 0; also in this case one needs to add an IF. (I am not
> sure whether it is always needed for CHARACTER but I play save.) The
> third case where one needs it is if one passes a deferred array dummy as
> actual argument to a non-deferred dummy as one here packs the array.
> 
> Build and regtested on x86-84-linux.
> OK for the trunk? The first part of the patch I also would like to
> backport to 4.4.

Ok, also for backport.

Thanks for the patch!

Daniel