Implementation of memory model

[Andrei Alexandrescu]

Hans,

A   memory  model  that  works  only  for  unoptimizing  builds  would
definitely be a letdown.

A  compiler  writer  would help by pointing out possible optimizations
that our abstraction either disables, or is too ambiguous to enable. I
could  fill  or  at  least  help  filling that role; I've been writing
optimizers for a couple of years.

Andrei

Thursday, September 23, 2004, 1:47:29 PM, you wrote:

> Andrei, Ben -

> I'm not sure exactly what kind of implementation effort we're talking
> about here.

> I think we're likely to come up with a memory model
> that would be satisfied by the current g++ -O0 on X86, IA64,
> SPARC TSO or PA (and probably many other compilers and platforms
> at minimal optimization).  Thus I expect that for this part
> we'll have an existence proof without doing any real work.
> We'll of course still need the opinions of compiler
> implementers as to the effect on current and future optimizations,
> though I think several of us have some reasonable understanding
> of those issues.  It would be good to have an optimizer that
> obeys whatever rules we propose, but I'm not sure it's either
> essential or terribly convincing, since I think any effect is
> likely to be very compiler- and architecture-dependent.

> We will of course need an implementation of the library components.
> But I'd be unhappy of that took a lot of new work.  I would guess
> that, for compilers that currently provide access to atomic operations
> and barriers via intrinsics or inline assembly, it should be possible
> to make a first pass at this without touching the compiler.

> Hans 

>> -----Original Message-----
>> From: Andrei Alexandrescu [mailto:andrei at metalanguage.com]
>> Sent: Friday, September 17, 2004 1:36 AM
>> To: Ben Hutchings
>> Cc: Hans Boehm; Kevlin Henney; Bill Pugh; Douglas C. Schmidt; Doug Lea
>> Subject: Re: Implementation of memory model
>> 
>> 
>> My hope is to convince Howard Hinnant to join us by using beer as
>> bribe.
>> 
>> Andrei
>> 
>> Thursday, September 16, 2004, 5:23:04 PM, you wrote:
>> 
>> > I expect that it will be necessary to get some 
>> implementation experience
>> > with any proposed memory model in order to produce a 
>> practical proposal
>> > that implementers will support and will adhere to if and 
>> when it becomes
>> > part of the next standard (or even before then).  It will 
>> surely benefit
>> > from Bill and Doug's experience with defining the Java 
>> memory model, but
>> > there are issues with C++ that don't arise in Java.
>> 
>> > Now correct me if I'm wrong, but I don't think any of you 
>> are involved
>> > in implementation of C++ compilers.  So I think we should 
>> try to get at
>> > least one implementer involved in this.  Perhaps you 
>> already planned to
>> > do this at the Redmond meeting, Andrei?  Alternately it may 
>> be possible
>> > for one or more of us to try out changes to GCC or EDG's 
>> C++ compiler,
>> > though I suspect that's much easier said than done.
>> 
>> > Ben.
>>