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Re: Inline DOT_PRODUCT revisited


Steven Bosscher wrote:
On Saturday 25 February 2006 23:47, Steven Bosscher wrote:

On Saturday 25 February 2006 23:37, Steven Bosscher wrote:

I would _very_ much like to have this patch in GCC 4.1.1

...the motivation being, of course, that the almost industry-standard Fortran benchmark (Polyhedron) benefits from this patch tremendeously,


...like so:

Before patch:
induct Run #   1   281.69211   281.69211 - Error=100.0000%

After patch:
induct Run #   1    45.12120    45.12120 - Error=100.0000%

I had hoped that the reduction support in the vectorizer would help
improve things further, but unfortunately with vectorization enabled
and the patch applied, we are slower (at least, on my AMD64 box) than
with vectorization disabled:
induct Run #   1    54.64700    54.64700 - Error=100.0000%

By simple mental arithmetic, SSE parallel instructions have no chance of speeding up reduction, until the operand length is 8 or more.


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