MAINT: Make the NPY_CPU_DISPATCH_CALL macros expressions not statements

[eric-wieser]

This means they can return values, and need semicolons.

Not tested locally, but the constructs were tested in godbolt.

ping @seiko2plus

[seiko2plus]

@eric-wieser, flexibility and unify one behavior among all dispatching macros are the two reasons that forced me to use normal if-condition over the ternary condition. can I know your reasons?

[eric-wieser]

can I know your reasons?

The main motivation here is that expressions are great, and making the result of the call an expression means I can use it like any other function call.

Note that I haven't touched the generated headers - those were flexible enough that I could just change the NPY_CPU ones.

[eric-wieser]

Note that these could now be rewritten

Suggested change

	NPY_CPU_DISPATCH_CALL(highest_func = _umath_tests_dispatch_func, ());
	NPY_CPU_DISPATCH_CALL(highest_var = _umath_tests_dispatch_var);
	highest_func = NPY_CPU_DISPATCH_CALL(_umath_tests_dispatch_func)();
	highest_var = NPY_CPU_DISPATCH_CALL(_umath_tests_dispatch_var);

Since this is a test, I decided to leave them as they are for now.

[seiko2plus]

You can just change one of them so we can test both behaviors.

[seiko2plus]

The main motivation here is that expressions are great, and making the result of the call an expression means I can use it like any other function call.

I will always vote for flexibility/hackability especially when you don't know "how deep the rabbit hole goes".
I see another thing here that may be reducing the flexibility will force the contributors towards safety, and I guess
this patch wouldn't harm that much we can always add new macros to serve different needs or even handle it locally in the case of #16960.

those were flexible enough that I could just change the NPY_CPU one

We can speed up the multiple calls of NPY_CPU_HAVE by inlining npy_cpu_have and extern the local variable npy__cpu_have which will give a good hint to the compiler without the need to change the NPY_CPU(CHK) one.

numpy/numpy/core/src/common/npy_cpu_features.h

Lines 111 to 115 in 60f9c61

	NPY_VISIBILITY_HIDDEN int
	npy_cpu_have(int feature_id);
	#define NPY_CPU_HAVE(FEATURE_NAME) \
	npy_cpu_have(NPY_CPU_FEATURE_##FEATURE_NAME)

numpy/numpy/core/src/common/npy_cpu_features.c.src

Line 9 in 60f9c61

static unsigned char npy__cpu_have[NPY_CPU_FEATURE_MAX];

[seiko2plus]

Suggested change

	* Same as `NPY_CPU_DISPATCH_DECLARE` but exclude the baseline declaration even
	* Same as `NPY_CPU_DISPATCH_CALL` but exclude the baseline call even

[Qiyu8]

I think this patch increases readability at the expense of a bit of unity, I'm confused the first time I saw NPY_CPU_DISPATCH_CALL and need to figure out it's expanded form, Glad to see this function-like style.

[Qiyu8]

the if statement is easier to read, why use the conditional expression?

[eric-wieser]

Because the conditional expression makes this have a return value

[mattip]

Thanks @eric-wieser