pub static STEP_VM_FASTPRED_FIRE: AtomicU64Expand description
v7.39 (round 481) — how many values the stack still holds when a call finishes, and how many are heap-bearing.
Round 480 left drop_glue<Value> at 16 % of self time with the drops
attributed to the predicate closure, i.e. to the stack rather than to
the returned value (round 479 removed that one). Whether the ops leave
operands behind for the next call’s clear() to drop is a question
with a number, so this counts it rather than reasoning about it — the
previous round was spent acting on an inference that turned out to name
an unreachable branch.
v7.39 (round 482) — how often the <column> <cmp> <literal> fast
predicate fires, so “is it even reached” is a number and not a guess
(round 480 was spent on a branch that turned out to be unreachable).