[issue4896] Faster why variable manipulation in ceval.c

[Paolo 'Blaisorblade' Giarrusso]

Paolo 'Blaisorblade' Giarrusso <p.giarrusso at gmail.com> added the comment:

Given a 10% speedup on some systems, and statistically insignificant
changes on other systems, I would still apply the patch, even simply
because the bitmask part simply makes more sense.

I'm not sure about the goto part, but still, it does straighten the
code. Anyway, simply call the label "why_is_WHY_NOT",
"why_set_to_WHY_NOT" or something like that. Verbosity on a use-once
label used with goto should be encouraged - we're not Java programmer,
but we need to pay for using goto by increasing readability in other ways.

@collinwinter: since the differences you report are so low (similar to
the statistical noise I get on my machine), I would expect that you're
just getting statistical noise instead of different results depending on
the GCC version, unless you performed statistical hypothesis testing
(confidence intervals and related stuff). And if I had done the needed
tens/hundreds of repetitions for hypothesis testing, I'd state that
clearly, so I suppose you didn't, and that's fully acceptable since the
result is likely to be statistically insignificant anyway.

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