[Info-vax] LLVM, volatile and async VMS I/O and system calls

[Dave Froble]

On 10/3/2021 7:32 PM, chris wrote:
> On 10/03/21 19:18, Dave Froble wrote:
>
>>
>> What I find a bit funny is all an optimizer does is corrects poorly
>> written code. People get into habits, and it can be hard to break some
>> habits.
>>
>> As an example, back in the day, the RSTS Basic+ interpreter had an
>> interesting quirk. For example:
>>
>> A = "abc"
>> B = A
>>
>> One would expect the value in A to be placed in the location where the
>> pointer to B points. However, Basic+ would change the pointer to B to
>> the value of the pointer to A, thus losing the old location of B. I
>> think this happened with strings, don't really remember, it has been a
>> very long time.
>>
>> Now consider that the pointer to B was in an I/O buffer. After the
>> operation, B would no longer be pointing into the I/O buffer. Perhaps
>> not such a good thing. (Actually a horrible thing!)
>>
>> What people learned to do is:
>>
>> B = A + ""
>>
>> That would insure moving of the data, not the pointer. With BP2 and
>> later, this odd operation was not an issue. But, even today, I find
>> people still using that old habit of appending the null string to an
>> operation.
>>
>> Bad habits are hard to kill.
>>
>
> Interesting. Never familiar with Basic, but looks like an empty
> string is being concatenated onto the existing string and forcing
> a read of the original and subsequent write of B, ensuring
> consistency ? So what happens if the null string is omitted ?...
>
> Chris

Now, nothing unusual.  That was a Basic+ quirk.  All compiled Basic does 
the right thing.

-- 
David Froble                       Tel: 724-529-0450
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