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

[Dave Froble]

On 9/27/2021 5:39 PM, chris wrote:
> On 09/27/21 19:49, Simon Clubley wrote:
>
>
> Yes,. it does, but the compiler has no knowledge of that at all, as it's
> a run time thing, not compile time. Unless the compiler has a crystal
> ball :-). Can have no idea of what underlying code might modify the
> buffer.

Obviously true.

This whole discussion isn't, or at least should not be, about compilers. 
  Perhaps interpreters, but let's not add more confusion.

> No, volatile does no such thing. It's merely a hint to the complier to
> apply no optimisation to it.

Correct.

> Quite common in interrupt handlers, but again, the compiler can't
> predict the future as to when it will be modified, or by whom,
> so how can it add code to mitigate what it can't understand ?.

I don't think that it does.

> That's how this started, right, VMS sys$qio having bugs internally ?.

Not that I recall.  The original issue was optimization on x86, if I 
remember correctly.  No guarantee of that.


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