[ptr-compr] Add a header for pointer compression related code

Bug: v8:7703
Change-Id: I96fd746291aa2e1386ed40068d38f5140bb1e44f
Reviewed-on: https://chromium-review.googlesource.com/c/1342031Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57612}

BUILD.gn

@@ -2410,6 +2410,7 @@ v8_source_set("v8_base") {
     "src/property.cc",
     "src/property.h",
     "src/prototype.h",
+    "src/ptr-compr.h",
     "src/regexp/bytecodes-irregexp.h",
     "src/regexp/interpreter-irregexp.cc",
     "src/regexp/interpreter-irregexp.h",

src/isolate-allocator.cc

@@ -5,6 +5,7 @@
 #include "src/isolate-allocator.h"
 #include "src/base/bounded-page-allocator.h"
 #include "src/isolate.h"
+#include "src/ptr-compr.h"
 #include "src/utils.h"
 
 namespace v8 {
@@ -43,15 +44,15 @@ Address IsolateAllocator::InitReservation() {
   // Reserve a 4Gb region so that the middle is 4Gb aligned.
   // The VirtualMemory API does not support such an constraint so we have to
   // implement it manually here.
-  size_t reservation_size = size_t{4} * GB;
-  size_t base_alignment = size_t{4} * GB;
+  size_t reservation_size = kPtrComprHeapReservationSize;
+  size_t base_alignment = kPtrComprIsolateRootAlignment;
 
   const int kMaxAttempts = 3;
   for (int attempt = 0; attempt < kMaxAttempts; ++attempt) {
     Address hint = RoundDown(reinterpret_cast<Address>(
                                  platform_page_allocator->GetRandomMmapAddr()),
                              base_alignment) +
-                   base_alignment / 2;
+                   kPtrComprIsolateRootBias;
 
     // Within this reservation there will be a sub-region with proper alignment.
     VirtualMemory padded_reservation(platform_page_allocator,
@@ -62,9 +63,9 @@ Address IsolateAllocator::InitReservation() {
     // Find such a sub-region inside the reservation that it's middle is
     // |base_alignment|-aligned.
     Address address =
-        RoundUp(padded_reservation.address() + reservation_size / 2,
+        RoundUp(padded_reservation.address() + kPtrComprIsolateRootBias,
                 base_alignment) -
-        reservation_size / 2;
+        kPtrComprIsolateRootBias;
     CHECK(padded_reservation.InVM(address, reservation_size));
 
     // Now free the padded reservation and immediately try to reserve an exact
@@ -81,8 +82,9 @@ Address IsolateAllocator::InitReservation() {
     // The reservation could still be somewhere else but we can accept it
     // if the reservation has the required alignment.
     Address aligned_address =
-        RoundUp(reservation.address() + reservation_size / 2, base_alignment) -
-        reservation_size / 2;
+        RoundUp(reservation.address() + kPtrComprIsolateRootBias,
+                base_alignment) -
+        kPtrComprIsolateRootBias;
 
     if (reservation.address() == aligned_address) {
       reservation_ = std::move(reservation);
@@ -96,7 +98,7 @@ Address IsolateAllocator::InitReservation() {
 
   CHECK_EQ(reservation_.size(), reservation_size);
 
-  Address heap_base = reservation_.address() + reservation_size / 2;
+  Address heap_base = reservation_.address() + kPtrComprIsolateRootBias;
   CHECK(IsAligned(heap_base, base_alignment));
 
   return heap_base;

src/isolate.cc

@@ -52,6 +52,7 @@
 #include "src/objects/stack-frame-info-inl.h"
 #include "src/profiler/tracing-cpu-profiler.h"
 #include "src/prototype.h"
+#include "src/ptr-compr.h"
 #include "src/regexp/regexp-stack.h"
 #include "src/runtime-profiler.h"
 #include "src/setup-isolate.h"
@@ -2728,8 +2729,9 @@ Isolate* Isolate::New(IsolateAllocationMode mode) {
   void* isolate_ptr = isolate_allocator->isolate_memory();
   Isolate* isolate = new (isolate_ptr) Isolate(std::move(isolate_allocator));
 #ifdef V8_TARGET_ARCH_64_BIT
-  DCHECK_IMPLIES(mode == IsolateAllocationMode::kInV8Heap,
-                 IsAligned(isolate->isolate_root(), size_t{4} * GB));
+  DCHECK_IMPLIES(
+      mode == IsolateAllocationMode::kInV8Heap,
+      IsAligned(isolate->isolate_root(), kPtrComprIsolateRootAlignment));
 #endif
 
 #ifdef DEBUG

src/ptr-compr.h

+// 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_PTR_COMPR_H_
+#define V8_PTR_COMPR_H_
+
+#if V8_TARGET_ARCH_64_BIT
+
+#include "src/globals.h"
+
+namespace v8 {
+namespace internal {
+
+constexpr size_t kPtrComprHeapReservationSize = size_t{4} * GB;
+constexpr size_t kPtrComprIsolateRootBias = kPtrComprHeapReservationSize / 2;
+constexpr size_t kPtrComprIsolateRootAlignment = size_t{4} * GB;
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_TARGET_ARCH_64_BIT
+
+#endif  // V8_PTR_COMPR_H_