8320382: Remove CompressedKlassPointers::is_valid_base()

Reviewed-by: rkennke, aph

Author: tstuefe

src/hotspot/share/cds/metaspaceShared.cpp

@@ -141,11 +141,16 @@ size_t MetaspaceShared::core_region_alignment() {
 }
 
 static bool shared_base_valid(char* shared_base) {
-#ifdef _LP64
-  return CompressedKlassPointers::is_valid_base((address)shared_base);
-#else
-  return true;
-#endif
+  // We check user input for SharedBaseAddress at dump time. We must weed out values
+  // we already know to be invalid later.
+
+  // At CDS runtime, "shared_base" will be the (attempted) mapping start. It will also
+  // be the encoding base, since the the headers of archived base objects (and with Lilliput,
+  // the prototype mark words) carry pre-computed narrow Klass IDs that refer to the mapping
+  // start as base.
+  //
+  // Therefore, "shared_base" must be later usable as encoding base.
+  return AARCH64_ONLY(is_aligned(shared_base, 4 * G)) NOT_AARCH64(true);
 }
 
 class DumpClassListCLDClosure : public CLDClosure {
@@ -1257,12 +1262,6 @@ char* MetaspaceShared::reserve_address_space_for_archives(FileMapInfo* static_ma
   if (base_address != nullptr) {
     assert(is_aligned(base_address, archive_space_alignment),
            "Archive base address invalid: " PTR_FORMAT ".", p2i(base_address));
-#ifdef _LP64
-    if (Metaspace::using_class_space()) {
-      assert(CompressedKlassPointers::is_valid_base(base_address),
-             "Archive base address invalid: " PTR_FORMAT ".", p2i(base_address));
-    }
-#endif
   }
 
   if (!Metaspace::using_class_space()) {
@@ -1348,7 +1347,6 @@ char* MetaspaceShared::reserve_address_space_for_archives(FileMapInfo* static_ma
            "Sanity (" PTR_FORMAT " vs " PTR_FORMAT ")", p2i(base_address), p2i(total_space_rs.base()));
     assert(is_aligned(total_space_rs.base(), archive_space_alignment), "Sanity");
     assert(total_space_rs.size() == total_range_size, "Sanity");
-    assert(CompressedKlassPointers::is_valid_base((address)total_space_rs.base()), "Sanity");
 
     // Now split up the space into ccs and cds archive. For simplicity, just leave
     //  the gap reserved at the end of the archive space. Do not do real splitting.

src/hotspot/share/oops/compressedKlass.cpp

@@ -39,7 +39,6 @@ size_t CompressedKlassPointers::_range = 0;
 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
 // archived heap objects.
 void CompressedKlassPointers::initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift) {
-  assert(is_valid_base(requested_base), "Address must be a valid encoding base");
   address const end = addr + len;
 
   const int narrow_klasspointer_bits = sizeof(narrowKlass) * 8;
@@ -89,23 +88,6 @@ void CompressedKlassPointers::initialize(address addr, size_t len) {
   set_base(base);
   set_shift(shift);
   set_range(range);
-
-  assert(is_valid_base(_base), "Address must be a valid encoding base");
-}
-
-// Given an address p, return true if p can be used as an encoding base.
-//  (Some platforms have restrictions of what constitutes a valid base address).
-bool CompressedKlassPointers::is_valid_base(address p) {
-#ifdef AARCH64
-  // Below 32G, base must be aligned to 4G.
-  // Above that point, base must be aligned to 32G
-  if (p < (address)(32 * G)) {
-    return is_aligned(p, 4 * G);
-  }
-  return is_aligned(p, (4 << LogKlassAlignmentInBytes) * G);
-#else
-  return true;
-#endif
 }
 
 void CompressedKlassPointers::print_mode(outputStream* st) {

src/hotspot/share/oops/compressedKlass.hpp

@@ -62,11 +62,6 @@ class CompressedKlassPointers : public AllStatic {
 
 public:
 
-  // Given an address p, return true if p can be used as an encoding base.
-  //  (Some platforms have restrictions of what constitutes a valid base
-  //   address).
-  static bool is_valid_base(address p);
-
   // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
   // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
   // archived heap objects.