🚀 go-pugleaf

In article <15767@vail.ICO.ISC.COM>, rcd@ico.ISC.COM (Dick Dunn) writes:
> In article <952@aber-cs.UUCP>, pcg@aber-cs.UUCP (Piercarlo Grandi) writes:
> [much deleted]

> > support for my position on "register" (where a competent programmer is
> > expected to do this, with great simplication of the compiler, because
> > compilers cannot possibly know which variables are the most frequently used
> > dynamically).
> 
> Where did this idea come from, and what can we do to send it back???
> All it takes for the compiler to allocate based on dynamic frequency is
> the right information from an execution profile.  (Q to MIPS folk--don't
> you have tools for this right now?)  In practice it may be tedious to
> develop a compiler system to do this, but the principle is simple:  Compile
> the program once with lots of instrumentation to gather frequency-of-use

One of our optimizers allocates registers by estimating useage. To handle
loops, it assums each loop is executed a small number of times. This does
much better register allocation than I do manually. It does not use profile
data. 

I once modified the optimizer to use the true count, when it could be
determined (many loops are done a constant number of times that can
be determined at optimization time, especially in benchmarks :-)   )
This did not improve the execution time of any of the benchmarks tested,
beyond what assuming they were executed a small number of times.

I thought about using execution-time profiles to improve optimization,
but that just opened up the can of  worms of determining what "typical data"
to use for the profiling run. At least, MIPS do this.

-- 
Jean-David Beyer
AT&T Bell Laboratories
Holmdel, New Jersey, 07733
attunix!beyer