6916623: Align object to 16 bytes to use Compressed Oops with java heap up to 64Gb

Added new product ObjectAlignmentInBytes flag to control object alignment.

Reviewed-by: twisti, ysr, iveresov

hotspot/src/share/vm/runtime/arguments.cpp

@@ -1211,8 +1211,44 @@ void Arguments::set_cms_and_parnew_gc_flags() {
 }
 #endif // KERNEL
 
+void set_object_alignment() {
+  // Object alignment.
+  assert(is_power_of_2(ObjectAlignmentInBytes), "ObjectAlignmentInBytes must be power of 2");
+  MinObjAlignmentInBytes     = ObjectAlignmentInBytes;
+  assert(MinObjAlignmentInBytes >= HeapWordsPerLong * HeapWordSize, "ObjectAlignmentInBytes value is too small");
+  MinObjAlignment            = MinObjAlignmentInBytes / HeapWordSize;
+  assert(MinObjAlignmentInBytes == MinObjAlignment * HeapWordSize, "ObjectAlignmentInBytes value is incorrect");
+  MinObjAlignmentInBytesMask = MinObjAlignmentInBytes - 1;
+
+  LogMinObjAlignmentInBytes  = exact_log2(ObjectAlignmentInBytes);
+  LogMinObjAlignment         = LogMinObjAlignmentInBytes - LogHeapWordSize;
+
+  // Oop encoding heap max
+  OopEncodingHeapMax = (uint64_t(max_juint) + 1) << LogMinObjAlignmentInBytes;
+
+#ifndef KERNEL
+  // Set CMS global values
+  CompactibleFreeListSpace::set_cms_values();
+#endif // KERNEL
+}
+
+bool verify_object_alignment() {
+  // Object alignment.
+  if (!is_power_of_2(ObjectAlignmentInBytes)) {
+    jio_fprintf(defaultStream::error_stream(),
+                "error: ObjectAlignmentInBytes=%d must be power of 2", (int)ObjectAlignmentInBytes);
+    return false;
+  }
+  if ((int)ObjectAlignmentInBytes < BytesPerLong) {
+    jio_fprintf(defaultStream::error_stream(),
+                "error: ObjectAlignmentInBytes=%d must be greater or equal %d", (int)ObjectAlignmentInBytes, BytesPerLong);
+    return false;
+  }
+  return true;
+}
+
 inline uintx max_heap_for_compressed_oops() {
-  LP64_ONLY(return oopDesc::OopEncodingHeapMax - MaxPermSize - os::vm_page_size());
+  LP64_ONLY(return OopEncodingHeapMax - MaxPermSize - os::vm_page_size());
   NOT_LP64(ShouldNotReachHere(); return 0);
 }
 
@@ -1776,6 +1812,8 @@ bool Arguments::check_vm_args_consistency() {
   status = status && verify_interval(TLABWasteTargetPercent,
                                      1, 100, "TLABWasteTargetPercent");
 
+  status = status && verify_object_alignment();
+
   return status;
 }
 
@@ -2848,6 +2886,9 @@ jint Arguments::parse(const JavaVMInitArgs* args) {
   UseCompressedOops = false;
 #endif
 
+  // Set object alignment values.
+  set_object_alignment();
+
 #ifdef SERIALGC
   force_serial_gc();
 #endif // SERIALGC

hotspot/src/share/vm/runtime/globals.hpp

@@ -321,6 +321,9 @@ class CommandLineFlags {
   diagnostic(bool, PrintCompressedOopsMode, false,                          \
             "Print compressed oops base address and encoding mode")         \
                                                                             \
+  lp64_product(intx, ObjectAlignmentInBytes, 8,                             \
+          "Default object alignment in bytes, 8 is minimum")                \
+                                                                            \
   /* UseMembar is theoretically a temp flag used for memory barrier         \
    * removal testing.  It was supposed to be removed before FCS but has     \
    * been re-added (see 6401008) */                                         \

hotspot/src/share/vm/runtime/vmStructs.cpp

@@ -1328,14 +1328,6 @@ static inline uint64_t cast_uint64_t(size_t x)
   declare_constant(LogBytesPerWord)                                       \
   declare_constant(BytesPerLong)                                          \
                                                                           \
-  /********************/                                                  \
-  /* Object alignment */                                                  \
-  /********************/                                                  \
-                                                                          \
-  declare_constant(MinObjAlignment)                                       \
-  declare_constant(MinObjAlignmentInBytes)                                \
-  declare_constant(LogMinObjAlignmentInBytes)                             \
-                                                                          \
   /********************************************/                          \
   /* Generation and Space Hierarchy Constants */                          \
   /********************************************/                          \