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

[christoph.goettschkes at microdoc.com]

Hi,

I already send this RFR to the hotspot-compiler-dev mailing list but 
didn't
get any response, so I am cross-posting the request here:

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