How best to write a series of related test_bit() calls?

[David Howells <dhowells@xxxxxxxxxx>]

I have a situation where I want to do something that boils down to:

	if (test_bit(BIT_A, &p->flags) {
	   	...
	} else if (test_bit(BIT_B, &p->flags) {
		...
	} else if (test_bit(BIT_C, &p->flags) {
		...
	} else if (test_bit(BIT_D, &p->flags) {
		...
	} else if (test_bit(BIT_E, &p->flags) {
	}

Note that all bits are in the same unsigned long and I don't necessarily
expect the contents of p->flags to change whilst I'm looking at it.

Since the address parameter for test_bit() contains a 'volatile' keyword, the
compiler will emit a separate load (or bit test) for each condition when in
fact the most efficient way is almost certainly one load and a bunch of
bitwise-and or bit-test-in-register instructions.

Is it worth adding a __test_bit() that doesn't have the volatile?  Or should I
just rewrite it manually as?

	unsigned long flags = p->flags;
	if (test_bit(BIT_A, &flags) {
	   	...
	} else if (test_bit(BIT_B, &flags) {
	...

Or even:

	unsigned long flags = p->flags;
	if ((1 << BIT_A) & flags) {
	   	...
	} else if ((1 << BIT_B) & flags) {
	...

David
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