bytes, strings: Compare tests do not modify input alignments

[mundaym]

I can't see any tests varying the alignment of Compare arguments. Since Compare is written in assembly on most platforms (in internal/bytealg) we should probably be checking that it works even if the inputs are unaligned.

[LotusFenn]

I'm interested in working on this. This would require making changes to the bytes/compare_test.go, is that correct? Thanks!

[mundaym]

@LotusFenn Yes, bytes/compare_test.go and strings/compare_test.go. An additional short test in each that just varies the input alignment from, say, 0 to 16 (inclusive) would be great. Thanks!

[gopherbot]

Change https://golang.org/cl/122536 mentions this issue: bytes: vary the input alignment to Compare argument in compare_test.go

[agnivade]

@mundaym - The Compare function in strings does not use assembly and has a simple implementation.

	if a == b {
		return 0
	}
	if a < b {
		return -1
	}
	return +1

It even has a note from @rsc saying -

	// NOTE(rsc): This function does NOT call the runtime cmpstring function,
	// because we do not want to provide any performance justification for
	// using strings.Compare. Basically no one should use strings.Compare.

Would you still want to test unaligned input for strings/compare_test.go ?

[mundaym]

@agnivade Good point. I still think it would be worthwhile though. The compiler could do the substitution with runtime.cmpstring or other alignment-sensitive vector code under the hood (as rsc alluded to in that comment).