Testing machine descriptions

[Niranjan Hasabnis]

Hello,

I am very curious to know what kind of testing techniques are applied to
machine description files. To be precise, is there any unit-testing environment
when some instructions are added/removed from MD file, or any other testing
technique is applied? Also, when MD file is patched to fix a bug, what kind of
tests are done on it?

I'm very much interested in knowing compiler internals and hence this question.
Thank you.

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Regards,
Niranjan Hasabnis.