Introduce Assembler.closeAligned.

Author: rschatz

compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/asm/Assembler.java

@@ -198,8 +198,24 @@ public void emitString(String s, int pos) {
      *            including) {@code position()} is returned
      * @return the data in this buffer or a trimmed copy if {@code trimmedCopy} is {@code true}
      */
-    public byte[] close(boolean trimmedCopy) {
+    public final byte[] close(boolean trimmedCopy) {
+        return closeAligned(trimmedCopy, 0);
+    }
+
+    /**
+     * Closes this assembler. No extra data can be written to this assembler after this call.
+     *
+     * @param trimmedCopy if {@code true}, then a copy of the underlying byte array up to (but not
+     *            including) {@code position()} is returned
+     * @param alignment if {@code > 0}, then align the end of the code buffer with NOPs to the
+     *            specified alignment
+     * @return the data in this buffer or a trimmed copy if {@code trimmedCopy} is {@code true}
+     */
+    public byte[] closeAligned(boolean trimmedCopy, int alignment) {
         checkAndClearLabelsWithPatches();
+        if (alignment > 0 && position() % alignment != 0) {
+            this.align(alignment);
+        }
         finalCodeSize = position();
         return codeBuffer.close(trimmedCopy);
     }