A simple optimization proposal

[Martin Grajcar]

Hi Kris,

some comments on
http://cr.openjdk.java.net/~kmo/8003585/webrev.02/src/share/vm/opto/subnode.cpp.sdiff.html

I could imagine adding cmp1->in(*1*) == cmp2 as an alternative at line
1217. While hardly anybody writes a.length & index, some previous
transformation could rearrange the expression.

The description at line 1221 mentions unsigned compare only while you're
handling both. I'm unsure about the correctness in the signed case (but
didn't check it). Some sort of proof would be nice, especially for extreme
values.

I like the idea at line 1237, though I don't exactly understand how it
works. Is there a good description of all the nodes and all normalizations
done?

Regards,
Martin.
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