1 /* 2 * Copyright (c) 2017, 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_OOPS_COMPRESSEDOOPS_INLINE_HPP 26 #define SHARE_OOPS_COMPRESSEDOOPS_INLINE_HPP 27 28 #include "gc/shared/collectedHeap.hpp" 29 #include "memory/universe.hpp" 30 #include "oops/oop.hpp" 31 32 // Functions for encoding and decoding compressed oops. 33 // If the oops are compressed, the type passed to these overloaded functions 34 // is narrowOop. All functions are overloaded so they can be called by 35 // template functions without conditionals (the compiler instantiates via 36 // the right type and inlines the appropriate code). 37 38 // Algorithm for encoding and decoding oops from 64 bit pointers to 32 bit 39 // offset from the heap base. Saving the check for null can save instructions 40 // in inner GC loops so these are separated. 41 42 namespace CompressedOops { is_null(oop obj)43 inline bool is_null(oop obj) { return obj == NULL; } is_null(narrowOop obj)44 inline bool is_null(narrowOop obj) { return obj == 0; } 45 decode_not_null(narrowOop v)46 inline oop decode_not_null(narrowOop v) { 47 assert(!is_null(v), "narrow oop value can never be zero"); 48 address base = Universe::narrow_oop_base(); 49 int shift = Universe::narrow_oop_shift(); 50 oop result = (oop)(void*)((uintptr_t)base + ((uintptr_t)v << shift)); 51 assert(check_obj_alignment(result), "address not aligned: " INTPTR_FORMAT, p2i((void*) result)); 52 return result; 53 } 54 decode(narrowOop v)55 inline oop decode(narrowOop v) { 56 return is_null(v) ? (oop)NULL : decode_not_null(v); 57 } 58 encode_not_null(oop v)59 inline narrowOop encode_not_null(oop v) { 60 assert(!is_null(v), "oop value can never be zero"); 61 assert(check_obj_alignment(v), "Address not aligned"); 62 assert(Universe::heap()->is_in_reserved(v), "Address not in heap"); 63 address base = Universe::narrow_oop_base(); 64 int shift = Universe::narrow_oop_shift(); 65 uint64_t pd = (uint64_t)(pointer_delta((void*)v, (void*)base, 1)); 66 assert(OopEncodingHeapMax > pd, "change encoding max if new encoding"); 67 uint64_t result = pd >> shift; 68 assert((result & CONST64(0xffffffff00000000)) == 0, "narrow oop overflow"); 69 assert(decode(result) == v, "reversibility"); 70 return (narrowOop)result; 71 } 72 encode(oop v)73 inline narrowOop encode(oop v) { 74 return is_null(v) ? (narrowOop)0 : encode_not_null(v); 75 } 76 77 // No conversions needed for these overloads decode_not_null(oop v)78 inline oop decode_not_null(oop v) { return v; } decode(oop v)79 inline oop decode(oop v) { return v; } encode_not_null(narrowOop v)80 inline narrowOop encode_not_null(narrowOop v) { return v; } encode(narrowOop v)81 inline narrowOop encode(narrowOop v) { return v; } 82 } 83 84 #endif // SHARE_OOPS_COMPRESSEDOOPS_INLINE_HPP 85