Questions about type annotation on type casts.
John Rose
john.r.rose at oracle.com
Mon Jan 18 08:29:44 UTC 2016
On Jan 17, 2016, at 10:52 PM, Srikanth <srikanth.adayapalam at oracle.com> wrote:
>
> By computing the offset just after translation of the expression, the offset would point to the checkcast instruction
> when present and when absent would point to the offset where the checkcast expression would have been had it not been optimized
> away - i.e pointing to the earliest offset where the fully finished expression value is at the top of stack.
>
> This appears to me to a better arrangement than what we have at present.
>
> Also note that we have the same eager offset computation issue with instanceof - I don't see the compilers optimizing away
> instanceof instructions as of now though.
That sounds good. One could think of the optimized checkcast as a zero-length opcode that leaves TOS unchanged.
If instanceof is optimized, it will turn into an iconst_[01]. That would be the instruction to point at, I suppose.
— John
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