8339635: StringConcatFactory optimization for CompactStrings off

Reviewed-by: liach

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

@@ -2642,6 +2642,10 @@ public Object stringConcat1(String[] constants) {
                 return new StringConcatHelper.Concat1(constants);
             }
 
+            public byte stringInitCoder() {
+                return String.COMPACT_STRINGS ? String.LATIN1 : String.UTF16;
+            }
+
             public int getCharsLatin1(long i, int index, byte[] buf) {
                 return StringLatin1.getChars(i, index, buf);
             }

src/java.base/share/classes/java/lang/invoke/StringConcatFactory.java

@@ -1196,9 +1196,14 @@ private static MethodTypeDesc prependArgs(MethodType concatArgs) {
 
         /**
          * Construct the MethodType of the coder method. The first parameter is the initialized coder.
-         * Only parameter types which can be UTF16 are added. Returns null if no such parameter exists.
+         * Only parameter types which can be UTF16 are added.
+         * Returns null if no such parameter exists or CompactStrings is off.
          */
         private static MethodTypeDesc coderArgsIfMaybeUTF16(MethodType concatArgs) {
+            if (JLA.stringInitCoder() != 0) {
+                return null;
+            }
+
             int parameterCount = concatArgs.parameterCount();
 
             int maybeUTF16Count = 0;

src/java.base/share/classes/jdk/internal/access/JavaLangAccess.java

@@ -459,6 +459,11 @@ public interface JavaLangAccess {
 
     Object stringConcat1(String[] constants);
 
+    /**
+     * Get the string initial coder, When COMPACT_STRINGS is on, it returns 0, and when it is off, it returns 1.
+     */
+    byte stringInitCoder();
+
     /**
      * Join strings
      */