RFR: 8309295: C2: MaxNode::signed_min() returns nullptr for int operands

Fri Jun 2 04:04:07 UTC 2023

This *trivial* changeset ensures that `MaxNode::signed_min()` returns a new `MinI` node, instead of `nullptr`, when receiving int arguments. This path is currently dead in the VM, but fixing it makes the functionality reusable (for example by JDK-8302673, currently [under review](https://github.com/openjdk/jdk/pull/13924)), more readable, and less error-prone.

#### Testing

- tier1-3 (windows-x64, linux-x64, linux-aarch64, macosx-x64, macosx-aarch64; release and debug mode).

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Commit messages:
 - Fix signed int min case in MaxNode::build_min_max()

Changes: https://git.openjdk.org/jdk/pull/14272/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14272&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309295
  Stats: 7 lines in 1 file changed: 3 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14272.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14272/head:pull/14272

PR: https://git.openjdk.org/jdk/pull/14272