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+### Performance
+
+- **A `throw` inside a counted loop no longer forces the loop off its fast
+  path.** `for (let i = 0; i < arr.length; i++) { if (bad) throw new Error(…);
+  sum += arr[i]; }` is the ordinary shape of a validating loop, and the throw
+  — even one that never fires — used to cost the whole packed-array
+  specialization. Measured on a quiet machine over a 512-element `number[]`:
+
+  | loop body | before | after | node |
+  |---|---|---|---|
+  | `throw new Error("bad")` | 7.99 ns/op | **0.95** | 7.70 |
+  | `throw new Error("bad " + i)` | 7.99 | **0.95** | 7.75 |
+  | `throw new Error()` | 7.99 | **0.95** | 7.75 |
+  | `throw "bad " + i` | 7.99 | **0.95** | 7.74 |
+  | `throw <pre-built value>` | 7.99 | **0.95** | 1.11 |
+
+  An 8.1× improvement on the constructing forms, which are the common ones.
+  Perry now runs every shape in that benchmark faster than node, including
+  the loop with no `throw` in it at all (0.95 against 1.11).
+
+  The specialization keeps a loop's accumulators in registers, so admitting a
+  `throw` required writing them back on the unwind edge — an exception leaves
+  through a landing pad rather than the loop's exit block, and a `catch` can
+  read anything the loop wrote. Operands are admitted only when evaluating
+  them cannot itself unwind: throwing a value coerces nothing, but building an
+  `Error` message or concatenating a string can dispatch to a user `toString`
+  or `valueOf`, and those can throw before the writeback runs.
+
+  These landed in **v0.5.1519** (#9235, with #9230 and #9215). This fragment
+  was written after that release was cut, so it appears here rather than in
+  the notes for the release that carries the change.