[stdlib] Minor enhancements

lorentey · lorentey · commit bbb004854ea0 · 2022-04-10T16:49:01.000-07:00
diff --git a/stdlib/public/core/StringUnicodeScalarView.swift b/stdlib/public/core/StringUnicodeScalarView.swift
@@ -143,7 +143,7 @@ extension String.UnicodeScalarView: BidirectionalCollection {
         _utf8ScalarLength(utf8, endingAt: i._encodedOffset)
       }
       _internalInvariant(len <= 4, "invalid UTF8")
-      return i.encoded(offsetBy: -len)._scalarAligned._knownUTF8
+      return i.encoded(offsetBy: 0 &- len)._scalarAligned._knownUTF8
     }
 
     return _foreignIndex(before: i)
diff --git a/stdlib/public/core/UnicodeHelpers.swift b/stdlib/public/core/UnicodeHelpers.swift
@@ -178,6 +178,7 @@ extension _StringGuts {
 
   @inline(never) // slow-path
   @_alwaysEmitIntoClient // Swift 5.1
+  @_effects(releasenone)
   internal func scalarAlignSlow(_ idx: Index) -> Index {
     _internalInvariant_5_1(!idx._isScalarAligned)
 

Original file line number	Diff line number	Diff line change
`@@ -143,7 +143,7 @@ extension String.UnicodeScalarView: BidirectionalCollection {`
`143`	`143`	`_utf8ScalarLength(utf8, endingAt: i._encodedOffset)`
`144`	`144`	`}`
`145`	`145`	`_internalInvariant(len <= 4, "invalid UTF8")`
`146`		`- return i.encoded(offsetBy: -len)._scalarAligned._knownUTF8`
	`146`	`+ return i.encoded(offsetBy: 0 &- len)._scalarAligned._knownUTF8`
`147`	`147`	`}`
`148`	`148`
`149`	`149`	`return _foreignIndex(before: i)`