[aarch64-port-dev ] RFR(M): 8233743: AArch64: Make r27 conditionally allocatable

[Andrew Haley]

On 11/29/19 6:40 AM, Nick Gasson wrote:
> On 29/11/2019 11:41, Pengfei Li (Arm Technology China) wrote:
>> The 4G alignment search may still fail after the fix. Regarding to my second webrev, do you agree that checking the base and shift values in a function in aarch64.ad? See my last email [1] for detail explanations.
>>
> How about we exit with a fatal error if we can't find a suitably aligned 
> region? Then we can remove the code in decode_klass_non_null that uses 
> R27 and this patch is much simpler. That code path is poorly tested at 
> the moment so it seems risky to leave it in. With a hard error at least 
> users will report it to us so we can fix it.

That is starting to sound very attractive. With a 64-bit address space I'm
finding it very hard to imagine a scenario in which we don't find a
suitable address. I think AOT-compiled code would still be OK, because it
generates different code, but we'd have to do some testing.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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