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

[Erik Österlund]

Hi Andrew,

On 2018-11-07 11:46, Andrew Dinn wrote:
> 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
> heap_base.
>
> It's all very devious!

Agreed.

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

Yes I think that would help for future adventurers stumbling across this 
code.

Thanks,
/Erik

> regards,
>
>
> Andrew Dinn
> -----------
> Senior Principal Software Engineer
> Red Hat UK Ltd
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