Re: [Freepooma-devel] [PATCH] Optimize Vector arithmetic

[Richard Guenther]

On Wed, 24 Nov 2004, Richard Guenther wrote:

> On Tue, 23 Nov 2004, Richard Guenther wrote:
>
> > Hi!
> >
> > Due to some oversight(??), Vector arithmetic is severely pessimized by
> > explicit creation of temporary Vectors.  The attached patch "fixes" that
> > by removing the casts to Vector<...,Full> from the VectorOperators.
> > This tests ok, it even generates the same code as handwritten loops, but
> > there has to be a reason the code was like it was?
> >
> > So, please test this on your favorite Vector-using code.  And report
> > breakage and/or performance.

Here's an updated patch with fixed what can be easily fixed.
Unfortunately with a non-optimizing compiler (-O0) we get extra
failures:

-PASSED ... array_test3
+FAILED ... array_test3
-PASSED ... array_test5
+FAILED ... array_test5
-PASSED ... array_test16
+FAILED ... array_test16
-PASSED ... array_test18
-PASSED ... array_test22
+FAILED ... array_test22

where array_test18 does not build due to the Stencil issue.

There has to be some we-use-a-reference-to-temporary around, as
doing optimized builds fixes the above failures.  Obviously it's
nearly impossible to stare at unoptimized assembly, and compilers
are not very helpful in issuing diagnostics either.

I tried the Intel compiler which spits out a warning for every

void foo(const int& x);
void bar() { foo(1); }

in that we create temporary storage and pass a reference to that
temporary by reference.  And that happens often.  Very.

But maybe someone has a good non-EDG based C++ compiler.

Suspending the Vector speedup for now,
Richard.