RFR: 8240615: is_power_of_2() has Undefined Behaviour and is inconsistent

[Andrew Haley]

On 3/9/20 12:20 PM, Stefan Karlsson wrote:
> On 2020-03-09 11:54, Andrew Haley wrote:
>> So, my plan is to push http://cr.openjdk.java.net/~aph/8240615-1/ and
>> subsequently patch a few AArch64 cases plus the x86_64 immL_Pow2 and
>> immL_NotPow2 cases that we already identified.
>>
>> I do not intend to do bulk changes to any other clients of
>> is_power_of_2() because it's often unclear exactly what behaviour is
>> required, and I'd risk breaking something.
>>
>> OK?
> 
> I would prefer if the x86_64 and aarch64 patches were pushed first, or 
> folded into this patch. Otherwise, we knowingly introduce a regression 
> by pushing the proposed patch above. However, I'll leave it up to the 
> compiler devs/maintainers to decide if this is OK.

We already have a regression in that AArch64 generates incorrect code.
IMO it's likely other targets do too.

However, I'm happy to push the x86_64 and aarch64 patches first or
as part of this patch.

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