JEP 401 verification with strict fields #22697
Description
https://cr.openjdk.org/~dlsmith/jep401/jep401-20250926/specs/value-objects-jvms.html
In a value class, a field without its ACC_STATIC flag set must have its ACC_FINAL and ACC_STRICT_INIT flags set.
if_acmpeq and if_acmpne verification:
A newly-created value object of an uninitialized type is not yet fully-formed, and if_acmpeq would improperly expose its uninitialized state. So this change disallows the use of if_acmpeq with uninitialized types.
ifnonnull verification:
From test/hotspot/jtreg/runtime/valhalla/inlinetypes/verifier/UninitializedThisVerificationTest.java, this is also expected to throw a verification error.
Like if_acmpeq, ifnonnull is useless on an uninitialized type: the value is never null, so the non-null branch will always be taken.