finit-local-zero and default initialization

[Jerry DeLisle]

Asher Langton wrote:
> On 6/5/07, Steve Kargl <sgk@troutmask.apl.washington.edu> wrote:
>> On Tue, Jun 05, 2007 at 04:50:43PM -0700, Asher Langton wrote:
>> > I'm planning to add support for -finit-local-zero (PR20441), as well
>> > as for arbitrary default initializations specified at compile-time.
>> > One request from within LLNL has been for a way to control the default
>> > initialization values at runtime, via some simple library routines
>> > (set_default_integer, get_default_integer, etc.).  This would be very
>> > useful for debugging large codes without recompiling an entire
>> > project.  Any comments, suggestions, or objections?
>> >
>>
>> I think the compile time options would be quite useful.
>> Can you describe the runtime method?  Would
>>
>>    program test
>>    integer i
>>    print *, i
>>    end progrma test
>>
>> compile to (pseudocode of course)
>>
>>   if (getenv(RUNTIME_INITIALIZE))
>>     i = set_default_integer()
>>
>>   print i
>>   end
> 
> The default initializations would be done only if specified at compile
> time.  The runtime option would just change the values used for
> default initialization.  So if default initialization was specified at
> compile time, the compiled code would be something like:
> 
> i = get_default_integer()
> print i
> end
> 
> By default, get_default_integer() would evaluate to 0, but a different
> value could be specified at compile time (via a compiler flag) or at
> runtime by calling set_default_integer.  Then a user could write a
> driver program to do something like:
> 
> set_default_integer (-2147483648)
> call massive_program
> set_default_integer (2147483647)
> call massive_program
> 
> This would help to reveal problems arising from incorrectly initialized 
> values.
> 
I like this approach, no runtime penalty if default initialization flag not 
given at compile time.

Jerry