Vzeroupper hotspot bug
sandhya.viswanathan at intel.com
Fri Apr 17 21:34:21 UTC 2015
From: Viswanathan, Sandhya
Sent: Friday, April 17, 2015 1:41 PM
To: hotspot-compiler-dev at openjdk.java.net; 'Vladimir Kozlov'
Subject: Vzeroupper hotspot bug
With 32 byte width vectorization the JVM produces wrong results under certain circumstances for x86_64.
The Vzeroupper instruction introduced in String.equals, String.compareTo and OptimizeFill intrinsic/stubs in the following change set is the cause of the bug:
For 32 byte vectorization, YMM registers are used by the hotspot compiler and the register allocator can allocate these across intrinsic methods.
Vzeroupper in the intrinsic is clobbering upper 16 bytes in all the other YMM registers that are not touched in these methods and so our customers are seeing unexpected results.
We need your help to create an RFE for this problem.
I have created a patch that fixes the problem on Linux and I will send you the corresponding webrev to attach to the RFE.
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