8324523: Lilliput: if +UseCOH, always use the archive's encoding base and shift

Reviewed-by: rkennke

Author: tstuefe

src/hotspot/share/cds/metaspaceShared.cpp

@@ -1158,19 +1158,25 @@ MapArchiveResult MetaspaceShared::map_archives(FileMapInfo* static_mapinfo, File
           address cds_base = (address)static_mapinfo->mapped_base();
           address ccs_end = (address)class_space_rs.end();
           assert(ccs_end > cds_base, "Sanity check");
-#if INCLUDE_CDS_JAVA_HEAP
-          // We archived objects with pre-computed narrow Klass id. Set up encoding such that these Ids stay valid.
-          address precomputed_narrow_klass_base = cds_base;
-          const int precomputed_narrow_klass_shift = ArchiveBuilder::precomputed_narrow_klass_shift;
-          CompressedKlassPointers::initialize_for_given_encoding(
-            cds_base, ccs_end - cds_base, // Klass range
-            precomputed_narrow_klass_base, precomputed_narrow_klass_shift // precomputed encoding, see ArchiveBuilder
-            );
-#else
-          CompressedKlassPointers::initialize (
-            cds_base, ccs_end - cds_base // Klass range
+          if (INCLUDE_CDS_JAVA_HEAP || UseCompactObjectHeaders) {
+            // The CDS archive may contain narrow Klass IDs that were precomputed at archive generation time:
+            // - every archived java object header (only if INCLUDE_CDS_JAVA_HEAP)
+            // - every archived Klass' prototype   (only if +UseCompactObjectHeaders)
+            //
+            // In order for those IDs to still be valid, we need to dictate base and shift: base should be the
+            // mapping start, shift the shift used at archive generation time.
+            address precomputed_narrow_klass_base = cds_base;
+            const int precomputed_narrow_klass_shift = ArchiveBuilder::precomputed_narrow_klass_shift;
+            CompressedKlassPointers::initialize_for_given_encoding(
+              cds_base, ccs_end - cds_base, // Klass range
+              precomputed_narrow_klass_base, precomputed_narrow_klass_shift // precomputed encoding, see ArchiveBuilder
             );
-#endif // INCLUDE_CDS_JAVA_HEAP
+          } else {
+            // Let JVM freely chose encoding base and shift
+            CompressedKlassPointers::initialize (
+              cds_base, ccs_end - cds_base // Klass range
+              );
+          }
           // map_or_load_heap_region() compares the current narrow oop and klass encodings
           // with the archived ones, so it must be done after all encodings are determined.
           static_mapinfo->map_or_load_heap_region();