RFR: JDK-8213199: GC abstraction for Assembler::needs_explicit_null_check()

Andrew Dinn adinn at redhat.com
Wed Nov 7 10:46:18 UTC 2018

On 07/11/18 10:37, Erik Österlund wrote:
> Thanks for digging that up.

No problem. The funny thing is that I knew about this ad file function
and -- roughly -- what it would achieve in terms of the graph reshape
and subsequent code generation. However, I never put 2 + 2 together and
followed through with the conclusion that this would cause loads of oops
stored as zero to potentially be modelled by and dereferenced at address

It's all very devious!

Do you think a small explanatory comment in uses_implicit_null_check
pointing readers at gen_narrow_oop_implicit_null_checks might be worth


Andrew Dinn
Senior Principal Software Engineer
Red Hat UK Ltd
Registered in England and Wales under Company Registration No. 03798903
Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander

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