[9] RFR (M): 8068038: C2: large constant offsets aren't handled on SPARC

Vladimir Ivanov vladimir.x.ivanov at oracle.com
Thu Feb 25 22:09:31 UTC 2016


C2 doesn't handle large constant offsets ((>=2^12 bytes) on SPARC and 
simply bails out the compilation and marks the method as non-compilable.

It has severe performance impact For example, some Octane benchmarks 
suffer >10x slowdown.

The fix is to use variable-sized encoding and put large offsets in the 
register. It means that all match rules and instructions which depend on 
emit_form3_mem_reg become variable-sized as well and their size should 
be computed dynamically.

I verified C2 compilation times and code emission still takes ~3-4%.

Also, did some cleanups: got rid of size computations in 
MachSpillCopyNode::implementation and helper methods, refactored 
printing logic.

Testing: octane, JPRT.


Best regards,
Vladimir Ivanov

PS: there's an additional cleanup [1] in sparc.ad (mostly 32-bit SPARC 
removal, but also added some comments). It can go along with this fix or 
as part of the 32-bit SPARC complete removal (JDK-8150388). Let me know 
what do you prefer.

[1] http://cr.openjdk.java.net/~vlivanov/8068038/webrev.cleanup

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