I have been following the CACAO JVM development on ARM since 2008, back then CACAO was one of the first alternative JVM, to be used instead of Hotspot in combination with the OpenJDK 6 class libraries.

CACAO history dates back to 1997-1998 when CACAO was one of the first JIT compiler to be used instead of SUN’s Java JVM interpreter.

Today CACAO are being used in combination with OpenJDK 6 on architectures like ARM, MIPS and PPC where Oracle have not yet released code for a GPL licensed Hotspot JIT. CACAO are popular, see the Debian OpenJDK-6 popularity contest chart where up to 80% of all the Debian OpenJDK 6 JVM users have picked CACAO to be installed. This trend kept on since the beginning of 2009 up to the summer of 2011.

Carpe diem CACAO JVM!

During the summer of 2011 Oracle released OpenJDK 7 and CACAO users started to abandon the JVM in favour for JamVM, the reason “why?” are that CACAO depends on the HPI API that have been removed from the OpenJDK 7 code base. This means that CACAO currently only work in combination with the “classic” OpenJDK 6. The second black cloud for CACAO JVM on ARM was that all major ARM Linux distributions started to move from “armel” towards the new “armhf” ABI something CACAO do not support. JamVM here provided the ARM Linux distributions and users with a stable and future proof alternative.

If we for a moment forget about the future and focus on today CACAO are in great shape when built from CACAO hg HEAD.

• CACAO are FAST, http://openjdk.gudinna.com/benchmarks/
• CACAO are stable, thanks to Stefan Ring who have been diligent on fixing bugs found in the CACAO JIT codegen.
• CACAO are fresh, the current CACAO hg HEAD contains the rewritten, “still unreleased” C++ version of CACAO its a totally different JVM compared to the last C based release of CACAO 0.99.4.

If you want to experience the CACAO JVM in its finest the do run the latest development version of CACAO in combination with OpenJDK 6, built using the current IcedTea6 head. Run it on ARM “armel”, PPC or MIPS and experience a fast responsive JVM burning brighter than ever before!

LLVM3.0 target feature matrix : http://llvm.org/docs/CodeGenerator.html#targetfeatures

LLVM 3.0 have been released

LLVM includes the JIT that can be used to speed up OpenJDK on all platforms that currently only have support by the platform independent Zero C++ hotspot port.

The JIT in LLVM have been redesigned from the ground up to use the same code path ways as used by the static compilation in LLVM by using the new MCJIT that in turn are based on the new direct Machine Code emission back-end. LLVM will over time drop support for the old “classic” jello-JIT.

OpenJDK Shark + LLVM 3.0 patches exist on zero-dev

I have posted some LLVM 3.0 patches to zero-dev that allows OpenJDK Shark to be built using this new MCJIT. Grab them all at: http://mail.openjdk.java.net/pipermail/zero-dev/2011-August/thread.html

Builds and testers are needed for MIPS, PPC and ARM

Shark are known to work stable on X86 hardware where all parts of LLVM have great community support. For all other architectures please check out the LLVM Target Feature Matrix.

According to this Target Feature Matrix table, MIPS JIT support are now GREEN! MIPS devs should try the OpenJDK + Shark + LLVM 3.0 combination, it could turn out to be really good. If you have a spare MIPS machine that are online 24/7 do consider adding it to the LLVM and IcedTea buildbot network!

For ARM the MACH-o JIT backend are supposed to be working, testers of OpenJDK + Shark + LLVM 3.0 on darwin based platforms like the iPhone and iPad please step forward, this combination looks to be working, at least on paper.

All ARM Linux users have to wait until the ELF MCJIT are stable before we can expect to run Shark using LLVM 3.0 and later.

PPC testers are also needed, LLVM support for PPC have been 90% good in the past.. it could be all broken or all working, no-one really know at least the LLVM darwin PPC buildbot shows some green lights but we currently do not have any IcedTea PPC buildbots to check if Shark + PPC work at all.