[Issue 18627] std.complex is a lot slower than builtin complex types at number crunching

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18627

--- Comment #8 from ponce <aliloko at gmail.com> ---
@Seb: It's not only about DMD, there is a 2x performance regression with
Complex!double vs cdouble using LDC. There are probably more I haven't exposed
yet. And yes, I use cdouble for designing IIR filters, in a real-time program.

Our main product use builtin complexes, it's downloaded 2000 times per month.

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