Re: Performance measurements

[Craig Burley <burley at gnu dot org>]

[Sorry I haven't tracked this thread; also I removed axp-list@redhat.com,
since my comments apply to only the x86 processor.]

>I also don't see the bad performance of egcs vs. gcc-2.7.2.3

My guess, not knowing what the code is (even its language), is that
this is due to the program being dependent mostly upon *static*
double-precision variables and arrays.

At least, that would explain the big difference in using
-malign-double over -mno-align-double on 2.7.2.3, especially
if g77 is the compiler being used.  Although, I'm at a loss
to understand why a small *opposite* difference is seen
using egcs 1.0.3a, which doesn't default to aligning static
doubles (based on my `align' package's output, anyway).

Even if stack-based doubles are used a lot, whether the bad
performance actually shows up in a benchmark can depend on
fairly random things -- the "original case" reported to
<fortran@gnu.org> being that the run-times differed *significantly*
depending on the length of the *name* of the executable!!

So it might be that 2.7.2.3 happened to naturally hit bad
alignments with -mno-align-double, nailed great ones (as should
normally, but not always, be the case) with -malign-double,
but none of the other runs happened to hit such black & white
alignments (e.g. maybe there are all either white, eggshell,
beige, or ecru ;-).

At this point, with the 1.1 freeze looming, I feel we have too
much more to learn about solving this problem right to try to
rush a quick fix into 1.1.  Though, I'm going to try and keep
it is a fairly top priority, to avoid having it slip until it's
too late to fix properly (or at least decide we can't do so) in 1.2.

        tq vm, (burley)