[stdlib] Document sources of code bloat

Author: lorentey

stdlib/public/core/ClosedRange.swift

@@ -68,6 +68,8 @@ public struct ClosedRange<Bound: Comparable> {
   /// The range's upper bound.
   public let upperBound: Bound
 
+  // This works around _debugPrecondition() impacting the performance of
+  // optimized code. (rdar://72246338)
   @_alwaysEmitIntoClient @inline(__always)
   internal init(_uncheckedBounds bounds: (lower: Bound, upper: Bound)) {
     self.lowerBound = bounds.lower

stdlib/public/core/Range.swift

@@ -157,6 +157,8 @@ public struct Range<Bound: Comparable> {
   /// instance does not contain its upper bound.
   public let upperBound: Bound
 
+  // This works around _debugPrecondition() impacting the performance of
+  // optimized code. (rdar://72246338)
   @_alwaysEmitIntoClient @inline(__always)
   internal init(_uncheckedBounds bounds: (lower: Bound, upper: Bound)) {
     self.lowerBound = bounds.lower

stdlib/public/core/UnsafeBufferPointer.swift.gyb

@@ -394,6 +394,8 @@ extension Unsafe${Mutable}BufferPointer: ${Mutable}Collection, RandomAccessColle
 }
 
 extension Unsafe${Mutable}BufferPointer {
+  // This works around _debugPrecondition() impacting the performance of
+  // optimized code. (rdar://72246338)
   @_alwaysEmitIntoClient
   internal init(
     @_nonEphemeral _uncheckedStart start: Unsafe${Mutable}Pointer<Element>?,