(j3.2006) (SC22WG5.4023) Late in the day question
Robert Corbett
Robert.Corbett
Thu Jun 25 01:30:16 EDT 2009
Andy Vaught wrote:
> On Tue, 23 Jun 2009 dick.hendrickson at att.net wrote:
>
>
>>It's my belief that FORALL was a mistake. Before a processor can
>>efficiently optimize a general FORALL construct it must prove a
>>bunch of theorems about left-to-right and line-to-line independence
>>and the theorems are almost identical to the ones it would have to
>>prove in order to vectorize a loop.
>
>
> ... and in the case that it can't, compiler-generated temporaries are
> required. Yuck. Making FORALL conceptually simple ended up making it
> almost worthless. Concurrent do is much better, even though it requires
> more care to use.
I don't know what you mean by the phrase "making FORALL conceptually
simple." I do not recall having before seen anyone assert that FORALL
construct is conceptually simple. In any case, the FORALL construct in
Fortran 95 and FORTRAN 2003 is largely the same as that of HPF 2.0.
What do you think the designers of HPF should have done differently to
make FORALL worthwhile?
In my work at Sun, I have had to explain what FORALL does to many users.
A lot of them thought that FORALL was a parallel DO.
Bob Corbett
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