The new .NET 10 feature for passing struct fields in registers does not appear to be working as advertized

### Type of issue

Code does not work

### Description

As documented in the following SO question:

https://stackoverflow.com/questions/79978180/why-does-net-10-jit-not-pass-struct-fields-in-registers-despite-physical-promot#comment141107350_79978180

I am not the author of this question but I have verified that it does not appear to be possible with the given steps to persuade the .NET 10 runtime into behaving as described.

### Page URL

https://learn.microsoft.com/en-us/dotnet/core/whats-new/dotnet-10/runtime#improved-code-generation-for-struct-arguments

### Content source URL

https://github.com/dotnet/docs/blob/main/docs/core/whats-new/dotnet-10/runtime.md

### Document Version Independent Id

64b4a915-2d72-9816-31a1-866ad593bb27

### Platform Id

489673e8-6332-c144-727a-e98fa5cea709

### Article author

@gewarren

### Metadata

* ID: 3357401d-36c1-995f-6b95-17865f4d58a5
* PlatformId: 489673e8-6332-c144-727a-e98fa5cea709
* Service: **dotnet-fundamentals**

[Related Issues](https://github.com/dotnet/docs/issues?q=is%3Aissue+is%3Aopen+64b4a915-2d72-9816-31a1-866ad593bb27)

Start with docs/core/whats-new/dotnet-10/runtime.md and its “Improved code generation for struct arguments” section, then reproduce the steps described in the linked Stack Overflow question. Compare the observed behavior with the article’s wording; done means the documentation accurately describes the supported behavior or clearly explains the limitation.

Written by the indexing model from the issue text.