'goto" gone from computer languages or is it!

[Jim Battle]

Dwight K. Elvey wrote:
...
> Hi
>  The last place I worked, the processor was designed to
> be able to optimize by doing out of order execution ( HaL
> computer system, first Sparc64 ). They soon discovered the
> problem when dealing with I/O. They, luckily, had a
> sequential mode that they could switch to during I/O
> operations that made the order predictable. You'd have
> thought that someone in the design team might have realized
> the problem.
> Dwight

Dwight, I'm more than a little sceptical that the architects at Hal 
didn't understand that reordering memory accesses would cause problems 
with programmed I/O.  I'm sure that they put in instruction 
serialization and  memory barrier instructions for precisely those 
reasons.  It wasn't a matter of "luckily" at all.

Even before OOO (out of order) execution at the instruction level was 
practical in the 90s, there were designs that performed memory access 
reordering since the 60s, leading to some of the same issues.

As a side note, I believe the first company to attempt (thought they 
didn't execute) real out of order instruction execution was Metaflow. 
Some have said that Metaflow's architectects (Bruce Lightner primarily) 
were ahead of their time, but the hallmark of good engineering is having 
the judgement to specifify something that can be built within 
constraints of practicality, not just specifying something with all the 
cool ideas you can come up with.