RFR: 8231955: ARM32: Address displacement is 0 for volatile field access because of Unsafe field access.

[dean.long at oracle.com]

The shared code used to call generate_address(), which correctly handles 
various displacements, but I guess it got lost in the barrier 
refactoring in jdk11.  I think the correct fix is for the caller to use 
generate_address() again.  CCing GC alias. Alternatively, the arm code 
could call generate_address rather than changing the shared code.

dl

On 10/15/19 12:30 AM, christoph.goettschkes at microdoc.com wrote:
> Is there anyone who could take a look at this change and give feedback
> please?
>
> Thanks,
> Christoph
>
> "hotspot-compiler-dev" <hotspot-compiler-dev-bounces at openjdk.java.net>
> wrote on 2019-10-10 16:29:11:
>
>> From: christoph.goettschkes at microdoc.com
>> To: hotspot-compiler-dev at openjdk.java.net
>> Date: 2019-10-10 16:35
>> Subject: RFR: 8231955: ARM32: Address displacement is 0 for volatile
> field
>> access because of Unsafe field access.
>> Sent by: "hotspot-compiler-dev"
> <hotspot-compiler-dev-bounces at openjdk.java.net>
>> Hi,
>>
>> please review the following changeset. This patch fixes the volatile
> field
>> access for 32-bit ARM. The functions LIRGenerator::volatile_field_store
>> and LIRGenerator::volatile_field_load both assume that the displacement
>> for the given address is always 0. Both use the given address and pass
> the
>> values to add_large_constant() [1], which asserts that the given
>> displacement is not 0. The change does not call add_large_constant if
> the
>> given displacement is 0. The displacement can be 0, because of the
>> implementation of the unsafe intrinsics. This happens, because the
> offset
>> into the object from which the field is accessed is not a constant
> value.
>> This fixes the hotspot tier1 tests mentioned in the issue.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8231955
>> Webrev: https://cr.openjdk.java.net/~bulasevich/8231955/webrev.00/
>>
>> Thanks,
>> Christoph
>>
>> [1]
>>
> https://hg.openjdk.java.net/jdk/jdk/file/30a9612a657d/src/hotspot/cpu/arm/
>> c1_LIRGenerator_arm.cpp#l166
>>