[Info-vax] Poulson info from Dave Cantor

[Bill Gunshannon]

In article <ic3qtf$9af$1 at news.eternal-september.org>,
	glen herrmannsfeldt <gah at ugcs.caltech.edu> writes:
> John Reagan <johnrreagan at earthlink.net> wrote:
> (snip)
> 
>> They are not MY compilers.   There are email addresses in the PPT slides 
>> that Tim posted.  Ask them.
>  
>>> The author writes: "Itanium relies on compilers to aggressively
>>> schedule instructions for parallel execution into bundles."
>>> What does "...aggressivively schedule..." mean in terms of compiler
>>> design ?
> 
> I would ask in comp.compilers.  It is moderated, but that is where
> the people that really know compilers are.
>  
>> To get good execution on Itanium, a compiler needs to analyze the code to 
>> figure out which things can be done in parallel or not.  It is then upto the 
>> compiler to organize those in bundles according to the bundle type (which 
>> only provides certain permutations).
>  
>> I suspect that code that runs today will run just fine in the future, but 
>> assumes that code that "runs" today isn't technically illegal.  Remember the 
>> situation with certain operations inside Alpha load-locked/store-conditional 
>> sequences?  They "worked" in early Alphas, but newer Alphas caught them.  We 
>> fixed the compilers but there was the worry that old .OBJs and .EXEs still 
>> are out there.  Thats where the CHECK_SRM tool (or whatever its name is) 
>> came from.  It lets you scan existing .EXEs to see if they have the bad 
>> seqeunces.
> 
> That tends to be a problem with RISC, and even worse with VLIW.
> 
> Note that IBM's z/OS running on z/Architecture machines currently
> in production will run object and executables written over 40 years
> ago for OS/360 on S/360 hardware.  There are incompatible changes
> in privileged instructions, but problem state code runs just fine.  
> 

It is my understanding that the same is true of Unisys.

bill

-- 
Bill Gunshannon          |  de-moc-ra-cy (di mok' ra see) n.  Three wolves
billg999 at cs.scranton.edu |  and a sheep voting on what's for dinner.
University of Scranton   |
Scranton, Pennsylvania   |         #include <std.disclaimer.h>