H. J. Lu wrote:
On Fri, Jun 15, 2007 at 06:21:53PM -0700, Ian Lance Taylor wrote:
This is hardly a new thought, but I believe that for the i386 gcc is
handicapped by reload. No matter how smart we are before reload, it
just take one poor decision by reload in an inner loop and we've lost
all the gains. Reload has enormous complexities which are mostly
irrelevant for the i386. And I think that the idea of doing register
allocation separately from spill code generation does not make sense
on the i386.
Why don't we turn on vectorizer at -O3 or even -O2, depending on
ISA? I added -ftree-vectorize to BOOT_CFLAGS on x86-64. According to
-ftree-vectorizer-verbose=1, there are 82 loops vectorized in
gcc source. There are no regressions. There are not much changes
in bootstrap time as well as "make check" time.
A mount ago I did some measurements of the effect of the vectorizer for
Core2 in 64-bit mode. Unfortunately, I saw small improvement (as I
remember less than 1% for SPECInt2000).
Vectorizer is a big a project and may be we will see more improvements
in future. They promissed implement SLP two years ago and now I see it
happens. It would be nice to see it not only in loops.
Vlad
