[Issue 22310] Template instantiation failures can be *very* costly

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22310

--- Comment #1 from kinke <kinke at gmx.net> ---
(In reply to kinke from comment #0)
> Note that failing to instantiate BooleanTypeOf!T for non-bool T also seems
> to lead to all successfully instantiated templates in there not to be cached
> (AliasThisTypeOf!T, OriginalType!T).

Scratch that, OriginalType!T *is* cached, only AliasThisTypeOf!T isn't,
possibly because of the speculative instantiation inside `static if (is(...))`.

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