Re: Patch to allow Ada to work with tree-ssa

[Geoffrey Keating <geoffk@geoffk.org>]

kenner@vlsi1.ultra.nyu.edu (Richard Kenner) writes:

>     Both have increased by a factor of between 21 and 22 in 5742 days.  A
>     1% increase every 18 days suffices to explain this.  What we do at -O0
>     should not be 20 times as complicated as what GCC 1.27 did at -O0.
> 
> Although I'm not arguing in favor of wasting memory, it's also imporant to
> look at the typical amounts of memory available at each of those times
> and see how it has increased as well.

This is a classic example of triple-counting.

Yes, main memory capacity has increased.  However, it is relatively
much slower compared to CPU speed, so the true comparison now is
between DRAM ten years ago and L2 cache now, which *isn't* much
larger.  In addition, programs have gotten larger, which soaks up much
of the CPU speed improvement.

Right now, one of the determining factors of GCC's speed is the number
of L2 cache misses it makes.  GCC spends much of its time waiting for
main memory.  It's like a machine ten years ago which was continuously
swapping.

>  I'm also not sure that -O0 is
> a good comparison point because the amount of data we keep is related
> to optimization issues and there's little motivation for have two
> different data structures and use one for optimized and the other for
> unoptimized code.

-O0 is the case that users care most about, because that's what they
use when they're in the edit-compile-debug cycle.

I don't believe you can compare -O2 between the two compilers and get
better results, though.  In fact, I think -O2 is relatively even slower.