1 /*
 2  * Copyright (c) 2023, Red Hat, Inc. All rights reserved.
 3  * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
 4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 5  *
 6  * This code is free software; you can redistribute it and/or modify it
 7  * under the terms of the GNU General Public License version 2 only, as
 8  * published by the Free Software Foundation.
 9  *
10  * This code is distributed in the hope that it will be useful, but WITHOUT
11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
13  * version 2 for more details (a copy is included in the LICENSE file that
14  * accompanied this code).
15  *
16  * You should have received a copy of the GNU General Public License version
17  * 2 along with this work; if not, write to the Free Software Foundation,
18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19  *
20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21  * or visit www.oracle.com if you need additional information or have any
22  * questions.
23  *
24  */
25 
26 #include "precompiled.hpp"
27 #include "oops/compressedKlass.hpp"
28 #include "utilities/globalDefinitions.hpp"
29 
30 char* CompressedKlassPointers::reserve_address_space_for_compressed_classes(size_t size, bool aslr, bool optimize_for_zero_base) {
31 
32   char* result = nullptr;
33 
34   // Optimize for base=0 shift=0; failing that, for base=0 shift>0
35   if (optimize_for_zero_base) {
36     result = reserve_address_space_for_unscaled_encoding(size, aslr);
37     if (result == nullptr) {
38       result = reserve_address_space_for_zerobased_encoding(size, aslr);
39     }
40   }
41 
42   // Optimize for a single 16-bit move: a base that has only bits set in its third quadrant [32..48).
43   if (result == nullptr) {
44     result = reserve_address_space_for_16bit_move(size, aslr);
45   }
46 
47   return result;
48 }


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