RFR: 8347365: C2: Fix the handling of depends_only_on_test

[Quan Anh Mai]

Hi,

This PR fixes the handling of `depends_only_on_test` when the control graph is transformed. It has to do with the theoretical idea of `depends_only_on_test`, copy from the JBS issue description:

To start with, what is `depends_only_on_test`? Given a node `n` with the control input `c`, if `c` can be deduced from `c'` and `n->depends_only_on_test() == true`, then we can rewire the control input of `n` to `c'`. This means that `depends_only_on_test` does not mean that the node depends on a test, it means that the node depends on the test that is its control input.

For example:

    if (y != 0) {
        if (x > 0) {
            if (y != 0) {
                x / y;
            }
        }
    }

Then `x/y` `depends_only_on_test` because its control input is the test `y != 0`. Then, we can rewire the control input of the division to the outer `y != 0`, resulting in:

    if (y != 0) {
        x / y;
        if (x > 0) {
        }
    }

On the other hand, consider this case:

    if (x > 0) {
        if (y != 0) {
            if (x > 0) {
                x / y;
            }
        }
    }

Then `x/y` does not `depends_only_on_test` because its control input is the test `x > 0` which is unrelated, we can see that if we rewire the division to the outer `x > 0` test, the division floats above the actual test `y != 0`. This means that `depends_only_on_test` is a dynamic property of a node, and not a static property of the division operation. It can change when we transform the graph and it can be different for different nodes of the same kind.

More details can be found in the description of `Node::depends_only_on_test` and `Node::pin_node_under_control` in this change.

Please take a look and leave your reviews, thanks a lot.

-------------

Commit messages:
 - Fix depends_only_on_test

Changes: https://git.openjdk.org/jdk/pull/29158/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29158&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8347365
  Stats: 418 lines in 22 files changed: 201 ins; 103 del; 114 mod
  Patch: https://git.openjdk.org/jdk/pull/29158.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29158/head:pull/29158

PR: https://git.openjdk.org/jdk/pull/29158