RFR: AArch64 Zero/SignExtend elision is inadequate

[Andrew Dinn]

I just posted PR #239 for review

  https://github.com/graalvm/graal/pull/239

It fixes the issue described in Issue #238

  https://github.com/graalvm/graal/issues/238

Review and pull would be welcome.

Testing:

This passes all unit tests including the newly added test which results
in many Sign/ZeorExtend operations.


regards,


Andrew Dinn
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Senior Principal Software Engineer
Red Hat UK Ltd
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