[PATCH, Fortran] Fix PR36112: Bounds-checking on character-array-constructors

[Daniel Kraft]

FX wrote:
> Hi Daniel,
> 
>> For array-constructors with all-constant string lengths, the compiler
>> pads the shorter strings to the maximum of all lengths', thus preventing
>> a runtime-error on different string lengths.  In this case, my patch now
>> emits a compiler-error for -fbounds-check.
> 
> -fbounds-check says it "enables generation of run-time checks". It 
> should not have any visible influence at compile-time. If the code is 
> determined to be illegal at compile-time, we should emit an error 
> unconditionaly. If the code can't be determined at compile-time, we will 
> do nothing if -fbounds-check is not given, and we will add run-time 
> checks if -fbounds-check is used (thus slowly down runtime performance 
> considerably, as you can imagine).

Ok, then I'll just make the error unconditionally.

> I have one more question: you add special cases for 
> get_array_ctor_var_strlen call() to allow it to be called with len == 
> NULL, but why? When (and where) is it called with a NULL argument?

Did I?  AFAIK, I added this NULL thing only to get_array_ctor_strlen, 
and not to any of the others (as this function not only calculates the 
length but also is_const); there it is called with NULL argument for 
sub-array-constructors not at the first position (thus where we are not 
interested in the length).

I'm not sure about how important is_const is, another (faster) approach 
would of course be to break the loop after we've found our length; but 
then we don't know about constness of following elements.

I'll provide an updated patch (with the condition on the error message 
and the XXX-mark removed) when the point above (and every other review 
details) are cleared, ok?

Thanks,
Daniel

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