Remove autorelease workaround for x86_64

stdlib/public/stubs/SwiftNativeNSXXXBaseARC.m

@@ -27,43 +27,18 @@
 // pool which might be scoped such that repeatedly placing objects into it
 // results in unbounded memory growth.
 
-// On i386 the remove from autorelease pool optimization is foiled by the
-// decomposedStringWithCanonicalMapping implementation. Instead, we use a local
-// autorelease pool to prevent leaking of the temporary object into the callers
-// autorelease pool.
-//
-//
-// FIXME: Right now we force an autoreleasepool here on x86_64 where we really
-// do not want to do so. The reason why is that without the autoreleasepool (or
-// really something like a defer), we tail call
-// objc_retainAutoreleasedReturnValue which blocks the hand shake. Evidently
-// this is something that we do not want to do. See:
-// b79ff50f1bca97ecfd053372f5f6dc9d017398bc. Until that is resolved, just create
-// an autoreleasepool here on x86_64. On arm/arm64 we do not have such an issue
-// since we use an assembly marker instead.
-#if defined(__i386__) || defined(__x86_64__)
-#define AUTORELEASEPOOL @autoreleasepool
-#else
-// On other platforms we rely on the remove from autorelease pool optimization.
-#define AUTORELEASEPOOL
-#endif
-
 SWIFT_CC(swift) SWIFT_RUNTIME_STDLIB_API
 size_t swift_stdlib_NSStringHashValue(NSString *str,
                                       bool isASCII) {
-  AUTORELEASEPOOL {
-    return isASCII ? str.hash : str.decomposedStringWithCanonicalMapping.hash;
-  }
+  return isASCII ? str.hash : str.decomposedStringWithCanonicalMapping.hash;
 }
 
 SWIFT_CC(swift) SWIFT_RUNTIME_STDLIB_API
 size_t
 swift_stdlib_NSStringHashValuePointer(void *opaque, bool isASCII) {
   NSString __unsafe_unretained *str =
       (__bridge NSString __unsafe_unretained *)opaque;
-  AUTORELEASEPOOL {
-    return isASCII ? str.hash : str.decomposedStringWithCanonicalMapping.hash;
-  }
+  return isASCII ? str.hash : str.decomposedStringWithCanonicalMapping.hash;
 }
 
 #else