Well, that's really just a sparse bug/misfeature that didn't matter
before.
It happens because the warning is done as part of constant expression
evaluation, but then the expression isn't actually *used*, so when we
optimize it away - at a later date - it's too late to undo the warning.
I don't rightly know how to fix it. We do want to do the constant
evaluation early (since all the optimizations that may then make it a
non-issue depends on constants being constants!), but in order to not
output the warning we'd have to turn the constant into a "constant with
warning 'xyz' if used".
Which we have no support for in sparse yet.
Linus
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