[mercury-users] Strange performance anomaly; can anyone confirm?

[Chris King]

While writing an n-queens implementation I encountered an anomaly
whereby simply wrapping the body of a predicate in a dummy if/then
causes a 2x speedup.  My code is attached (trimmed down as much as
possible), can anyone confirm?  I'm testing in the asm_fast.gc grade
on amd64.

My presumption is simply that the conditional is causing some
optimization to be triggered, but -O 6 doesn't seem to make a
difference.  Any thoughts?

Thanks,
Chris
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