8262994: Refactor String.split to help method inlining

Reviewed-by: plevart

src/java.base/share/classes/java/lang/String.java

@@ -3129,6 +3129,17 @@ public final class String
             (ch < Character.MIN_HIGH_SURROGATE ||
              ch > Character.MAX_LOW_SURROGATE))
         {
+            // All the checks above can potentially be constant folded by
+            // a JIT/AOT compiler when the regex is a constant string.
+            // That requires method inlining of the checks, which is only
+            // possible when the actual split logic is in a separate method
+            // because the large split loop can usually not be inlined.
+            return split(ch, limit);
+        }
+        return Pattern.compile(regex).split(this, limit);
+    }
+
+    private String[] split(char ch, int limit) {
         int off = 0;
         int next = 0;
         boolean limited = limit > 0;
@@ -3163,8 +3174,6 @@ public final class String
         String[] result = new String[resultSize];
         return list.subList(0, resultSize).toArray(result);
     }
-        return Pattern.compile(regex).split(this, limit);
-    }
 
     /**
      * Splits this string around matches of the given <a