Only use SIMD when stdlib vector types are available

Author: Catfish-Man

stdlib/cmake/modules/SwiftSource.cmake

@@ -300,6 +300,10 @@ function(_add_target_variant_swift_compile_flags
   if(SWIFT_STDLIB_ENABLE_UNICODE_DATA)
     list(APPEND result "-D" "SWIFT_STDLIB_ENABLE_UNICODE_DATA")
   endif()
+  
+  if(SWIFT_STDLIB_ENABLE_VECTOR_TYPES)
+    list(APPEND result "-D" "SWIFT_STDLIB_ENABLE_VECTOR_TYPES")
+  endif()
 
   if(SWIFT_STDLIB_HAS_COMMANDLINE)
     list(APPEND result "-D" "SWIFT_STDLIB_HAS_COMMANDLINE")

stdlib/public/core/StringUTF16View.swift

@@ -520,6 +520,7 @@ extension _StringGuts {
 
 extension String.UTF16View {
 
+#if SWIFT_STDLIB_ENABLE_VECTOR_TYPES
   @inline(__always)
   internal func _utf16Length<U: SIMD, S: SIMD>(
     readPtr: inout UnsafeRawPointer,
@@ -551,6 +552,7 @@ extension String.UTF16View {
 
     return utf16Count
   }
+#endif
 
   @inline(__always)
   internal func _utf16Distance(from start: Index, to end: Index) -> Int {
@@ -576,6 +578,7 @@ extension String.UTF16View {
         readPtr += 1
       }
 
+#if SWIFT_STDLIB_ENABLE_VECTOR_TYPES
       // TODO: Currently, using SIMD sizes above SIMD8 is slower
       // Once that's fixed we should go up to SIMD64 here
 
@@ -605,6 +608,7 @@ extension String.UTF16View {
           return 0
         }
       }
+#endif
 
       //trailing bytes
       while readPtr < endPtr {