Tests for lzcnt

Trevor Watson trevor.d.watson at oracle.com
Tue Nov 1 17:16:09 UTC 2016

I'm working on https://bugs.openjdk.java.net/browse/JDK-8162865, which 
implements the inlining of LZCNT instructions on SPARC platforms which 
support it.

I have the code implemented and have written a test-case that validates 
the values returned by Long.countLeadingZeros() and 

Looking through the hotspot tests, I see there is some testing of lzcnt 
in compiler/intrinsics/bmi. I've adapted TestLzcntI.java and 
TestLzcntL.java to check for the relevant SPARC feature as well as the 
x86/x64 feature. These tests work fine, but only validate that C2 
generates the same results as interpreted code for a selection of random 
values. Whilst that is perfectly valid, I'd like to also be able to 
verify that the inlined code for the lz count for each power of 2 in an 
Integer and Long produces correct values (per my standalone test).

Would the "bmi" directory be the appropriate place to add a new test 
like this or even hold a test which supports both x86/x64 and SPARC 
given that "bmi" appears to refer to some kind of x86/x64 cpu feature 
set? Or am I reading too much into "bmi" and its just used here as a 
generic name?

I hope that made sense.


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