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// Copyright 2018 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_COMMON_PTR_COMPR_INL_H_
#define V8_COMMON_PTR_COMPR_INL_H_
#include "include/v8-internal.h"
#include "src/common/ptr-compr.h"
#include "src/execution/isolate.h"
namespace v8 {
namespace internal {
#if V8_TARGET_ARCH_64_BIT
// Compresses full-pointer representation of a tagged value to on-heap
// representation.
V8_INLINE Tagged_t CompressTagged(Address tagged) {
return static_cast<Tagged_t>(static_cast<uint32_t>(tagged));
}
// Calculates isolate root value from any on-heap address.
template <typename TOnHeapAddress>
V8_INLINE Address GetIsolateRoot(TOnHeapAddress on_heap_addr);
template <>
V8_INLINE Address GetIsolateRoot<Address>(Address on_heap_addr) {
// We subtract 1 here in order to let the compiler generate addition of 32-bit
// signed constant instead of 64-bit constant (the problem is that 2Gb looks
// like a negative 32-bit value). It's correct because we will never use
// leftmost address of V8 heap as |on_heap_addr|.
return RoundDown<kPtrComprIsolateRootAlignment>(on_heap_addr +
kPtrComprIsolateRootBias - 1);
}
template <>
V8_INLINE Address GetIsolateRoot<Isolate*>(Isolate* isolate) {
Address isolate_root = isolate->isolate_root();
#ifdef V8_COMPRESS_POINTERS
isolate_root = reinterpret_cast<Address>(V8_ASSUME_ALIGNED(
reinterpret_cast<void*>(isolate_root), kPtrComprIsolateRootAlignment));
#endif
return isolate_root;
}
// Decompresses smi value.
V8_INLINE Address DecompressTaggedSigned(Tagged_t raw_value) {
// For runtime code the upper 32-bits of the Smi value do not matter.
return static_cast<Address>(raw_value);
}
// Decompresses weak or strong heap object pointer or forwarding pointer,
// preserving both weak- and smi- tags.
template <typename TOnHeapAddress>
V8_INLINE Address DecompressTaggedPointer(TOnHeapAddress on_heap_addr,
Tagged_t raw_value) {
// Current compression scheme requires |raw_value| to be sign-extended
// from int32_t to intptr_t.
intptr_t value = static_cast<intptr_t>(static_cast<int32_t>(raw_value));
Address root = GetIsolateRoot(on_heap_addr);
return root + static_cast<Address>(value);
}
// Decompresses any tagged value, preserving both weak- and smi- tags.
template <typename TOnHeapAddress>
V8_INLINE Address DecompressTaggedAny(TOnHeapAddress on_heap_addr,
Tagged_t raw_value) {
if (kUseBranchlessPtrDecompressionInRuntime) {
// Current compression scheme requires |raw_value| to be sign-extended
// from int32_t to intptr_t.
intptr_t value = static_cast<intptr_t>(static_cast<int32_t>(raw_value));
// |root_mask| is 0 if the |value| was a smi or -1 otherwise.
Address root_mask = static_cast<Address>(-(value & kSmiTagMask));
Address root_or_zero = root_mask & GetIsolateRoot(on_heap_addr);
return root_or_zero + static_cast<Address>(value);
} else {
return HAS_SMI_TAG(raw_value)
? DecompressTaggedSigned(raw_value)
: DecompressTaggedPointer(on_heap_addr, raw_value);
}
}
#ifdef V8_COMPRESS_POINTERS
STATIC_ASSERT(kPtrComprHeapReservationSize ==
Internals::kPtrComprHeapReservationSize);
STATIC_ASSERT(kPtrComprIsolateRootBias == Internals::kPtrComprIsolateRootBias);
STATIC_ASSERT(kPtrComprIsolateRootAlignment ==
Internals::kPtrComprIsolateRootAlignment);
#endif // V8_COMPRESS_POINTERS
#else
V8_INLINE Tagged_t CompressTagged(Address tagged) { UNREACHABLE(); }
V8_INLINE Address DecompressTaggedSigned(Tagged_t raw_value) { UNREACHABLE(); }
template <typename TOnHeapAddress>
V8_INLINE Address DecompressTaggedPointer(TOnHeapAddress on_heap_addr,
Tagged_t raw_value) {
UNREACHABLE();
}
template <typename TOnHeapAddress>
V8_INLINE Address DecompressTaggedAny(TOnHeapAddress on_heap_addr,
Tagged_t raw_value) {
UNREACHABLE();
}
#endif // V8_TARGET_ARCH_64_BIT
} // namespace internal
} // namespace v8
#endif // V8_COMMON_PTR_COMPR_INL_H_
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