Merge pull request #19664 from lorentey/dictionary-subscript-setter-is-slow

[stdlib] Speed up _Bitset in size-optimized builds

Author: lorentey

stdlib/public/core/Bitset.swift

@@ -38,7 +38,10 @@ extension _UnsafeBitset {
   @inline(__always)
   internal static func word(for element: Int) -> Int {
     _sanityCheck(element >= 0)
-    return element / Word.capacity
+    // Note: We perform on UInts to get faster unsigned math (shifts).
+    let element = UInt(bitPattern: element)
+    let capacity = UInt(bitPattern: Word.capacity)
+    return Int(bitPattern: element / capacity)
   }
 
   @inlinable
@@ -61,22 +64,22 @@ extension _UnsafeBitset {
   @inline(__always)
   internal static func join(word: Int, bit: Int) -> Int {
     _sanityCheck(bit >= 0 && bit < Word.capacity)
-    return word * Word.capacity + bit
+    return word &* Word.capacity + bit
   }
 }
 
 extension _UnsafeBitset {
   @inlinable
   @inline(__always)
   internal static func wordCount(forCapacity capacity: Int) -> Int {
-    return (capacity + Word.capacity - 1) / Word.capacity
+    return word(for: capacity + Word.capacity - 1)
   }
 
   @inlinable
   internal var capacity: Int {
     @inline(__always)
     get {
-      return wordCount * Word.capacity
+      return wordCount &* Word.capacity
     }
   }