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llxia
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May 31, 2023
Disable CLassLookahead because it is possible for static final field value to be changes via reflection or the unsafe API. 1. Disable ClassLookahead. Similar to GVP, ClassLookahead is using static analysis of static final field initialization code to provide field information that is later used to make assumptions about the field contents which might not be true if reflection or the unsafe API is used to change static final field values. An environment variable is introduced to allow ClassLookahead to be re-enable. 2. Apply a fix to ClassLookahead so that it does not not generate field information for static final fields that can be initialized with different values on different code paths. This fix is being applied in case the ClassLookahead code is resurrected in the future since `#1` above has disabled it globally. 3.Remove the code in IlGen what would replace array length checks with hard coded obj array length values. This code would look for static final fields that contain ClassLookahead fieldInfo and use the existence of that information to permit the inspection of a heap object and replace array length checks with a constant based on the current heap object's array length. This fix is also applied as a safety measure because the disabling of ClassLookahead (`eclipse-openj9#2` above) would effectively disable this code path. In general the only safe way to inspect at compile time heap objects pointed to by static final fields is to us the "Static Final Field Folding" optimization which uses OSR to invalidate any code which made an assumptions based on the contents of a static final field when that fields contents may have been modified by reflection. Signed-off-by: Kevin Langman <langman@ca.ibm.com>
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