stdlib: improve debug performance of UnsafePointer.pointer(to:)

Making those functions transparent enables to completely remove the creation of keypaths, even with -Onone.
rdar://127793797

Author: eeckstein

stdlib/public/core/UnsafePointer.swift

@@ -444,9 +444,7 @@ extension UnsafePointer {
   /// - Returns: A pointer to the stored property represented
   ///            by the key path, or `nil`.
   @_alwaysEmitIntoClient
-  #if $Embedded
   @_transparent
-  #endif
   public func pointer<Property>(
     to property: KeyPath<Pointee, Property>
   ) -> UnsafePointer<Property>? {
@@ -1332,9 +1330,7 @@ extension UnsafeMutablePointer {
   /// - Returns: A pointer to the stored property represented
   ///            by the key path, or `nil`.
   @_alwaysEmitIntoClient
-  #if $Embedded
   @_transparent
-  #endif
   public func pointer<Property>(
     to property: KeyPath<Pointee, Property>
   ) -> UnsafePointer<Property>? {
@@ -1356,9 +1352,7 @@ extension UnsafeMutablePointer {
   /// - Returns: A mutable pointer to the stored property represented
   ///            by the key path, or `nil`.
   @_alwaysEmitIntoClient
-  #if $Embedded
   @_transparent
-  #endif
   public func pointer<Property>(
     to property: WritableKeyPath<Pointee, Property>
   ) -> UnsafeMutablePointer<Property>? {

test/SILOptimizer/pointer-performance.swift

@@ -0,0 +1,17 @@
+// RUN: %target-swift-frontend %s -module-name=test -parse-as-library -emit-sil | %FileCheck %s
+
+// REQUIRES: swift_stdlib_no_asserts,optimized_stdlib
+
+public struct S {
+  var a: Int
+  var b: Int
+}
+
+// Check that even with -Onone, no keypath is created.
+
+// CHECK-LABEL: sil @$s4test6testitySPySiGSgSPyAA1SVGF :
+// CHECK-NOT:     keypath
+// CHECK:       } // end sil function '$s4test6testitySPySiGSgSPyAA1SVGF'
+public func testit(_ p: UnsafePointer<S>) -> UnsafePointer<Int>? {
+  return p.pointer(to: \.b)
+}