Re-instate "stdlib: Add some inlining attributes to help the optimizer getting the right inlining decisions."

This re-instates commit 8b0e36779e

stdlib/public/core/HashedCollections.swift.gyb

@@ -419,6 +419,7 @@ public struct Set<Element : Hashable> :
   /// Returns an iterator over the members.
   ///
   /// - Complexity: O(1).
+  @inline(__always)
   public func makeIterator() -> SetIterator<Element> {
     return _variantStorage.makeIterator()
   }
@@ -1038,6 +1039,7 @@ public struct Dictionary<Key : Hashable, Value> :
   /// Returns the `Index` for the given key, or `nil` if the key is not
   /// present in the dictionary.
   @warn_unused_result
+  @inline(__always)
   public func index(forKey key: Key) -> Index? {
     // Complexity: amortized O(1) for native storage, O(N) when wrapping an
     // NSDictionary.
@@ -1057,6 +1059,7 @@ public struct Dictionary<Key : Hashable, Value> :
   /// Writing `nil` as the value for a given key erases that key from
   /// `self`.
   public subscript(key: Key) -> Value? {
+    @inline(__always)
     get {
       return _variantStorage.maybeGet(key)
     }
@@ -1132,6 +1135,7 @@ public struct Dictionary<Key : Hashable, Value> :
   /// Returns an iterator over the `(Key, Value)` pairs.
   ///
   /// - Complexity: O(1).
+  @inline(__always)
   public func makeIterator() -> DictionaryIterator<Key, Value> {
     return _variantStorage.makeIterator()
   }
@@ -1951,6 +1955,7 @@ struct _Native${Self}Storage<${TypeParametersDecl}> :
   }
 
   @warn_unused_result
+  @inline(__always)
   internal func key(at i: Int) -> Key {
     _precondition(i >= 0 && i < capacity)
     _sanityCheck(isInitializedEntry(at: i))
@@ -2078,6 +2083,7 @@ struct _Native${Self}Storage<${TypeParametersDecl}> :
   /// If the key is not present, returns the position where it could be
   /// inserted.
   @warn_unused_result
+  @inline(__always)
   internal func _find(key: Key, startBucket: Int)
     -> (pos: Index, found: Bool) {
 
@@ -2164,6 +2170,7 @@ struct _Native${Self}Storage<${TypeParametersDecl}> :
   }
 
   @warn_unused_result
+  @inline(__always)
   internal func index(forKey key: Key) -> Index? {
     if count == 0 {
       // Fast path that avoids computing the hash of the key.
@@ -2199,6 +2206,7 @@ struct _Native${Self}Storage<${TypeParametersDecl}> :
   }
 
   @warn_unused_result
+  @inline(__always)
   internal func maybeGet(key: Key) -> Value? {
     if count == 0 {
       // Fast path that avoids computing the hash of the key.
@@ -2880,6 +2888,7 @@ internal struct _Cocoa${Self}Storage : _HashStorage {
   }
 
   @warn_unused_result
+  @inline(__always)
   internal func maybeGet(key: Key) -> Value? {
 
 %if Self == 'Set':
@@ -3118,6 +3127,7 @@ internal enum _Variant${Self}Storage<${TypeParametersDecl}> : _HashStorage {
   }
 
   @warn_unused_result
+  @inline(__always)
   internal func index(forKey key: Key) -> Index? {
     if _fastPath(guaranteedNative) {
       if let nativeIndex = asNative.index(forKey: key) {
@@ -3208,6 +3218,7 @@ internal enum _Variant${Self}Storage<${TypeParametersDecl}> : _HashStorage {
 #endif
 
   @warn_unused_result
+  @inline(__always)
   internal func maybeGet(key: Key) -> Value? {
     if _fastPath(guaranteedNative) {
       return asNative.maybeGet(key)
@@ -3528,6 +3539,7 @@ internal enum _Variant${Self}Storage<${TypeParametersDecl}> : _HashStorage {
   /// Returns an iterator over the `(Key, Value)` pairs.
   ///
   /// - Complexity: O(1).
+  @inline(__always)
   internal func makeIterator() -> ${Self}Iterator<${TypeParameters}> {
     switch self {
     case .native(let owner):
@@ -3988,6 +4000,7 @@ public struct ${Self}Iterator<${TypeParametersDecl}> : IteratorProtocol {
   /// element exists.
   ///
   /// - Precondition: No preceding call to `self.next()` has returned `nil`.
+  @inline(__always)
   public mutating func next() -> ${Sequence}? {
     if _fastPath(_guaranteedNative) {
       return _nativeNext()

stdlib/public/core/ManagedBuffer.swift

@@ -412,31 +412,43 @@ public struct ManagedBufferPointer<Value, Element> : Equatable {
 
   /// Offset from the allocated storage for `self` to the stored `Value`
   internal static var _valueOffset: Int {
+    @inline(__always)
+    get {
       return _roundUp(
         sizeof(_HeapObject.self),
         toAlignment: alignof(Value.self))
     }
+  }
 
   /// An **unmanaged** pointer to the storage for the `Value`
   /// instance.  Not safe to use without _fixLifetime calls to
   /// guarantee it doesn't dangle
   internal var _valuePointer: UnsafeMutablePointer<Value> {
+    @inline(__always)
+    get {
       return UnsafeMutablePointer(_address + _My._valueOffset)
     }
+  }
 
   /// An **unmanaged** pointer to the storage for `Element`s.  Not
   /// safe to use without _fixLifetime calls to guarantee it doesn't
   /// dangle.
   internal var _elementPointer: UnsafeMutablePointer<Element> {
+    @inline(__always)
+    get {
       return UnsafeMutablePointer(_address + _My._elementOffset)
     }
+  }
 
   /// Offset from the allocated storage for `self` to the `Element` storage
   internal static var _elementOffset: Int {
+    @inline(__always)
+    get {
       return _roundUp(
         _valueOffset + sizeof(Value.self),
         toAlignment: alignof(Element.self))
     }
+  }
 
   internal var _nativeBuffer: Builtin.NativeObject
 }

stdlib/public/core/StringBuffer.swift

@@ -201,6 +201,7 @@ public struct _StringBuffer {
   /// - parameter bounds: Range of the substring that the caller tries
   ///   to extend.
   /// - parameter newUsedCount: The desired size of the substring.
+  @inline(__always)
   mutating func grow(
     oldBounds bounds: Range<UnsafePointer<_RawByte>>, newUsedCount: Int
   ) -> Bool {

stdlib/public/core/StringCore.swift

@@ -307,6 +307,8 @@ public struct _StringCore {
 
   /// Get the Nth UTF-16 Code Unit stored.
   public subscript(position: Int) -> UTF16.CodeUnit {
+    @inline(__always)
+    get {
       _precondition(
         position >= 0,
         "subscript: index precedes String start")
@@ -324,6 +326,7 @@ public struct _StringCore {
       _sanityCheckFailure("subscript: non-native string without objc runtime")
 #endif
     }
+  }
 
   /// Write the string, in the given encoding, to output.
   func encode<
@@ -519,6 +522,7 @@ public struct _StringCore {
     _invariantCheck()
   }
 
+  @inline(never)
   mutating func append(rhs: _StringCore) {
     _invariantCheck()
     let minElementWidth

stdlib/public/core/StringUnicodeScalarView.swift

@@ -41,6 +41,7 @@ extension String {
         self.idx = pos
         self.core = core
       }
+      @inline(__always)
       mutating func next() -> UTF16.CodeUnit? {
         if idx == core.endIndex {
           return nil
@@ -61,6 +62,7 @@ extension String {
       ///
       /// - Precondition: The next value is representable.
       @warn_unused_result
+      @inline(__always)
       public func successor() -> Index {
         var scratch = _ScratchIterator(_core, _position)
         var decoder = UTF16()