[cpp-threads] RE: Review comments on N2176 WRT dependency ordering

[Boehm, Hans]

> -----Original Message-----
> From: Paul E. McKenney [mailto:paulmck at linux.vnet.ibm.com] 
> What is your reaction to the notion of dependency defined in 
> the Itanium and the POWER architecture documents?  Page 384 
> of my copy of volume 2 of the Itanium Architecture manual 
> defines a dependency from A to B as follows:
> 
> 	"A precedes B in program order and A produces a value that
> 	B consumes."
> 
I think that especially at the programming language level, this
introduces a large number of unclear corner cases:

1) When do library functions propagate dependencies?  Is there a
dependency from a character inserted into a string to the resulting
string size?  To the output of search for a certain substring?
2) What if the type involved has only one corresponding valid value?
3) In what sense is a value produced in a switch statement dependent on
the switch expression?
Etc.

It may be that this can be addressed.  But I don't think it's easy.  The
topic is certainly on my list of things to be discussed in Oxford.

Hans