RFR: JDK-8213473: Prevent transformation of LoadB->AndI->CmpI pattern to facilitate testb instruction matching

[Roman Kennke]

In JDK-8203628, Aleksey added matchers to generate testb instruction (on
x86) for LoadB->AndI->CmpI sequence. However, in AndINode::Ideal() we
transform any LoadB->AndI to LoadUB->AndI which fails to match this
pattern. Which means we never actually match for testb. The original
matchers for LoadUB->AndI->CmpI needed to be removed because of
JDK-8204479.

The proposed enhancement would prevent the transformation if we have a
straight LoadB->AndI->CmpI sequence. While the matcher is x86-only, I
don't think it actually hurts to prevent this particular sequence. It
should generate better code (e.g. single testb instructions) for things
like:

byte field;
..

if ((field & 3) == 0) ..

or even:

if (field == x) .. because we always mask byte loads

or even (not sure) same for boolean fields.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8213473
Webrev:
http://cr.openjdk.java.net/~rkennke/JDK-8213473/webrev.00/

Testing: passes hotspot/jtreg:tier1 here

Thoughts? Reviews?

Roman





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