diff --git a/compiler-rt/lib/lsan/lsan_allocator.h b/compiler-rt/lib/lsan/lsan_allocator.h
--- a/compiler-rt/lib/lsan/lsan_allocator.h
+++ b/compiler-rt/lib/lsan/lsan_allocator.h
@@ -49,8 +49,35 @@
   u32 stack_trace_id;
 };
 
-#if defined(__mips64) || defined(__aarch64__) || defined(__i386__) || \
-    defined(__arm__)
+#if defined(__aarch64__)
+template <typename AddressSpaceViewTy>
+struct AP32 {
+  static const uptr kSpaceBeg = 0;
+  static const u64 kSpaceSize = SANITIZER_MMAP_RANGE_SIZE;
+  static const uptr kMetadataSize = sizeof(ChunkMetadata);
+  typedef __sanitizer::CompactSizeClassMap SizeClassMap;
+  static const uptr kRegionSizeLog = 20;
+  using AddressSpaceView = AddressSpaceViewTy;
+  typedef NoOpMapUnmapCallback MapUnmapCallback;
+  static const uptr kFlags = 0;
+};
+
+template <typename AddressSpaceViewTy>
+struct AP64 {  // Allocator64 parameters. Deliberately using a short name.
+  static const uptr kSpaceBeg = 0x600000000000ULL;
+  static const uptr kSpaceSize = 0x40000000000ULL;  // 4T.
+  static const uptr kMetadataSize = sizeof(ChunkMetadata);
+  typedef DefaultSizeClassMap SizeClassMap;
+  typedef NoOpMapUnmapCallback MapUnmapCallback;
+  static const uptr kFlags = 0;
+  using AddressSpaceView = AddressSpaceViewTy;
+};
+
+template <typename AddressSpaceView>
+using PrimaryAllocatorASVT =
+    SizeClassAllocatorPair<AP64<AddressSpaceView>, AP32<AddressSpaceView>>;
+using PrimaryAllocator = PrimaryAllocatorASVT<LocalAddressSpaceView>;
+#elif defined(__mips64) || defined(__i386__) || defined(__arm__)
 template <typename AddressSpaceViewTy>
 struct AP32 {
   static const uptr kSpaceBeg = 0;
diff --git a/compiler-rt/lib/lsan/lsan_allocator.cc b/compiler-rt/lib/lsan/lsan_allocator.cc
--- a/compiler-rt/lib/lsan/lsan_allocator.cc
+++ b/compiler-rt/lib/lsan/lsan_allocator.cc
@@ -38,6 +38,13 @@
 
 void InitializeAllocator() {
   SetAllocatorMayReturnNull(common_flags()->allocator_may_return_null);
+#if defined(__aarch64__)
+  // 47+ bit Aarch64 address space needs a 64-bit allocator.
+  if (GetMaxVirtualAddress() < (((uptr)1 << 48) - 1))
+    allocator.Use2(); // 32-bit.
+  else
+    allocator.Use1(); // 64-bit.
+#endif
   allocator.InitLinkerInitialized(
       common_flags()->allocator_release_to_os_interval_ms);
 }
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_allocator.h b/compiler-rt/lib/sanitizer_common/sanitizer_allocator.h
--- a/compiler-rt/lib/sanitizer_common/sanitizer_allocator.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_allocator.h
@@ -75,6 +75,7 @@
 #include "sanitizer_allocator_local_cache.h"
 #include "sanitizer_allocator_secondary.h"
 #include "sanitizer_allocator_combined.h"
+#include "sanitizer_allocator_primary_pair.h"
 
 } // namespace __sanitizer
 
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary_pair.h b/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary_pair.h
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary_pair.h
@@ -0,0 +1,109 @@
+//===-- sanitizer_allocator_secondary.h -------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Part of the Sanitizer Allocator.
+//
+//===----------------------------------------------------------------------===//
+#ifndef SANITIZER_ALLOCATOR_H
+#error This file must be included inside sanitizer_allocator.h
+#endif
+
+static bool use1 = false;
+
+template <class A1, class A2>
+class SizeClassAllocatorPair {
+  A1 a1;
+  A2 a2;
+
+ public:
+  class AllocatorCache {
+    typename A1::AllocatorCache a1;
+    typename A2::AllocatorCache a2;
+
+   public:
+    void Init(AllocatorGlobalStats *s) {
+      if (use1)
+        return a1.Init(s);
+      return a2.Init(s);
+    }
+    void *Allocate(SizeClassAllocatorPair *allocator, uptr class_id) {
+      if (use1)
+        return a1.Allocate(&allocator->a1, class_id);
+      return a2.Allocate(&allocator->a2, class_id);
+    }
+
+    void Deallocate(SizeClassAllocatorPair *allocator, uptr class_id, void *p) {
+      if (use1)
+        return a1.Deallocate(&allocator->a1, class_id, p);
+      return a2.Deallocate(&allocator->a2, class_id, p);
+    }
+
+    void Drain(SizeClassAllocatorPair *allocator) {
+      if (use1)
+        return a1.Drain(&allocator->a1);
+      return a2.Drain(&allocator->a2);
+    }
+
+    void Destroy(SizeClassAllocatorPair *allocator, AllocatorGlobalStats *s) {
+      if (use1)
+        return a1.Destroy(&allocator->a1, s);
+      return a2.Destroy(&allocator->a2, s);
+    }
+  };
+
+  void Init(s32 release_to_os_interval_ms) {
+    if (use1)
+      return a1.Init(release_to_os_interval_ms);
+    return a2.Init(release_to_os_interval_ms);
+  }
+
+  void Use1() { use1 = true; }
+  void Use2() { use1 = false; }
+
+  static bool CanAllocate(uptr size, uptr alignment) {
+    if (use1)
+      return A1::CanAllocate(size, alignment);
+    return A2::CanAllocate(size, alignment);
+  }
+
+  static uptr ClassID(uptr size) {
+    if (use1)
+      return A1::ClassID(size);
+    return A2::ClassID(size);
+  }
+
+  bool PointerIsMine(const void *p) {
+    if (use1)
+      return a1.PointerIsMine(p);
+    return a2.PointerIsMine(p);
+  }
+
+  void *GetMetaData(const void *p) {
+    if (use1)
+      return a1.GetMetaData(p);
+    return a2.GetMetaData(p);
+  }
+
+  uptr GetSizeClass(const void *p) {
+    if (use1)
+      return a1.GetSizeClass(p);
+    return a2.GetSizeClass(p);
+  }
+
+  void ForEachChunk(ForEachChunkCallback callback, void *arg) {
+    if (use1)
+      return a1.ForEachChunk(callback, arg);
+    return a2.ForEachChunk(callback, arg);
+  }
+
+  void TestOnlyUnmap() {
+    if (use1)
+      return a1.TestOnlyUnmap();
+    return a2.TestOnlyUnmap();
+  }
+};