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Perf #859: elide per-char box round-trip in promoted-string charCodeAt (strings → parity) #873

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Merged
nickna merged 1 commit into from
Jun 21, 2026
Merged

Perf #859: elide per-char box round-trip in promoted-string charCodeAt (strings → parity) #873

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8 changes: 5 additions & 3 deletions Compilation/ILEmitter.Properties.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1276,15 +1276,17 @@ private void EmitPromotedStringCharCodeAt(LocalBuilder sb, List<Expr> arguments)
IL.Emit(OpCodes.Ldloc, idxLocal);
IL.Emit(OpCodes.Callvirt, getChars);
IL.Emit(OpCodes.Conv_R8);
IL.Emit(OpCodes.Box, _ctx.Types.Double);
IL.Emit(OpCodes.Br, end);

IL.MarkLabel(oob);
IL.Emit(OpCodes.Ldc_R8, double.NaN);
IL.Emit(OpCodes.Box, _ctx.Types.Double);

// #859: leave a raw float64 (both branches push double) instead of boxing. The result is
// typically consumed by a numeric op (`sum + s.charCodeAt(i)`), whose EnsureDouble is then a
// no-op; a boxed-object consumer re-boxes via EmitBoxIfNeeded (which checks StackType). This
// elides the per-char `box Double` (a heap allocation) plus the consumer's `ConvertToNumber`.
IL.MarkLabel(end);
SetStackUnknown();
SetStackType(StackType.Double);
}

/// <summary>
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