[Issue 21364] Passing a struct by-value adds padding that breaks argument access within the function

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21364

--- Comment #3 from Walter Bright <bugzilla at digitalmars.com> ---
Because of alignment, X.sizeof is 16. So the call is correct, but foo() gets it
wrong and treats the size as 12.

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