[lworld] RFR: 8352647: [lworld] Remove larval InlineTypeNode in Unsafe intrinsics

[Quan Anh Mai]

On Sat, 29 Mar 2025 22:41:26 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

> Yes, I agree, this should be seen on the lines of a primitive (value) meeting an identity object (boxes),

I think you are misunderstanding, the type `reference` here refers to a verification type that represents the most general reference type, it is even higher than `java.lang.Object`. From the JVMS:

    Verification type hierarchy:

                                 top
                     ____________/____________
                    /                          \
                   /                            \
                oneWord                       twoWord
               /   |   \                     /       \
              /    |    \                   /         \
            int  float  reference        long        double             <--- meeting of a larval value and a non-larval value results in the `reference` type here
                         /     \
                        /       _____________
                       /                      \
                      /                        \
               uninitialized                    +------------------+    <--- larval objects have their verification type being `uninitialized`
                /         \                     |  Java reference  |    <--- `java.lang.Object` and its subclasses are here
               /           \                    |  type hierarchy  |
    uninitializedThis  uninitialized(Offset)    +------------------+  
                                                         |
                                                         |
                                                        null

> Thus, here at merge point, MyValue should be buffered, since this is MEETing a larval value so new oop (Phi) should be larval, similar to following

Note that this implicit boxing and unboxing only happens at the language level, `javac` will automatically translate `ret = genInt(val)` into `ret = Integer.valueOf(genInt(val))`. So, at the VM level, we do not ever encounter a meet of a `java.lang.Integer` and an `int`. As a result, C2 does not have to take auto boxing and unboxing into consideration.

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PR Comment: https://git.openjdk.org/valhalla/pull/1406#issuecomment-2764355420