Comment (by Erik Schnetter):

In McLachlan, I find that the derivative operators themselves are quite large. I declare them CCTK_ATTRIBUTE_NOINLINE, but make their definition still available when compiling the caller. GCC then specializes the function, i.e. uses a special calling convention that is more efficient than the regular one.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2410/compiling-baikal-with-gcc-93-is-very-slow