stdlib: Address unreachable code warnings.

Author: tshortli

stdlib/public/core/StringUTF8View.swift

@@ -345,11 +345,11 @@ extension String.UTF8View {
 #endif
       let count = _guts.count
       if _guts.isSmall {
-        let a = Builtin.addressOfBorrow(self)
-        let address = unsafe UnsafePointer<UTF8.CodeUnit>(a)
-        let span = unsafe Span(_unsafeStart: address, count: count)
         fatalError("Span over the small string form is not supported yet.")
-        return unsafe _overrideLifetime(span, borrowing: self)
+//        let a = Builtin.addressOfBorrow(self)
+//        let address = unsafe UnsafePointer<UTF8.CodeUnit>(a)
+//        let span = unsafe Span(_unsafeStart: address, count: count)
+//        return unsafe _overrideLifetime(span, borrowing: self)
       }
       _precondition(_guts.isFastUTF8)
       let buffer = unsafe _guts._object.fastUTF8

stdlib/public/core/Substring.swift

@@ -789,12 +789,12 @@ extension Substring.UTF8View {
       let first = _slice._startIndex._encodedOffset
       let end = _slice._endIndex._encodedOffset
       if _wholeGuts.isSmall {
-        let a = Builtin.addressOfBorrow(self)
-        let offset = first &+ (2 &* MemoryLayout<String.Index>.stride)
-        let start = unsafe UnsafePointer<UTF8.CodeUnit>(a).advanced(by: offset)
-        let span = unsafe Span(_unsafeStart: start, count: end &- first)
         fatalError("Span over the small string form is not supported yet.")
-        return unsafe _overrideLifetime(span, borrowing: self)
+//        let a = Builtin.addressOfBorrow(self)
+//        let offset = first &+ (2 &* MemoryLayout<String.Index>.stride)
+//        let start = unsafe UnsafePointer<UTF8.CodeUnit>(a).advanced(by: offset)
+//        let span = unsafe Span(_unsafeStart: start, count: end &- first)
+//        return unsafe _overrideLifetime(span, borrowing: self)
       }
       _internalInvariant(_wholeGuts.isFastUTF8)
       var span = unsafe Span(_unsafeElements: _wholeGuts._object.fastUTF8)