That in itself is pretty significant. If that value would otherwise be
constant folded or strength-reduced away, you're putting a big
limitation on what the compiler can do. The mere fact that its
necessary to do something to preserve many values shows how much the
compiler transforms the code away from what's in the source, and
specifically referencing otherwise unused intermediates inhibits that.
In other words, if you weren't preventing optimisations, you wouldn't
need to preserve values as much, because the optimiser wouldn't be
getting rid of them. If you need to preserve lots of values, you're
necessarily preventing the optimiser from doing its job.
J
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