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diff --git a/js/src/jit/arm64/vixl/MozCachingDecoder.h b/js/src/jit/arm64/vixl/MozCachingDecoder.h
new file mode 100644
index 0000000000..5b4cfc17d5
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+++ b/js/src/jit/arm64/vixl/MozCachingDecoder.h
@@ -0,0 +1,179 @@
+#ifndef VIXL_A64_MOZ_CACHING_DECODER_A64_H_
+#define VIXL_A64_MOZ_CACHING_DECODER_A64_H_
+
+#include "mozilla/HashTable.h"
+
+#include "jit/arm64/vixl/Decoder-vixl.h"
+#include "js/AllocPolicy.h"
+
+#ifdef DEBUG
+#define JS_CACHE_SIMULATOR_ARM64 1
+#endif
+
+#ifdef JS_CACHE_SIMULATOR_ARM64
+namespace vixl {
+
+// This enumeration list the different kind of instructions which can be
+// decoded. These kind correspond to the set of visitor defined by the default
+// Decoder.
+enum class InstDecodedKind : uint8_t {
+  NotDecodedYet,
+#define DECLARE(E) E,
+  VISITOR_LIST(DECLARE)
+#undef DECLARE
+};
+
+// A SinglePageDecodeCache is used to store the decoded kind of all instructions
+// in an executable page of code. Each time an instruction is decoded, its
+// decoded kind is recorded in this structure. The previous instruction value is
+// also recorded in this structure when using a debug build.
+//
+// The next time the same offset is visited, the instruction would be decoded
+// using the previously recorded decode kind. It is also compared against the
+// previously recorded bits of the instruction to check for potential missing
+// cache invalidations, in debug builds.
+//
+// This structure stores the equivalent of a single page of code to have better
+// memory locality when using the simulator. As opposed to having a hash-table
+// for all instructions. However a hash-table is used by the CachingDecoder to
+// map the prefixes of page addresses to these SinglePageDecodeCaches.
+class SinglePageDecodeCache {
+ public:
+  static const uintptr_t PageSize = 1 << 12;
+  static const uintptr_t PageMask = PageSize - 1;
+  static const uintptr_t InstSize = vixl::kInstructionSize;
+  static const uintptr_t InstMask = InstSize - 1;
+  static const uintptr_t InstPerPage = PageSize / InstSize;
+
+  SinglePageDecodeCache(const Instruction* inst)
+    : pageStart_(PageStart(inst))
+  {
+    memset(&decodeCache_, int(InstDecodedKind::NotDecodedYet), sizeof(decodeCache_));
+  }
+  // Compute the start address of the page which contains this instruction.
+  static uintptr_t PageStart(const Instruction* inst) {
+    return uintptr_t(inst) & ~PageMask;
+  }
+  // Returns whether the instruction decoded kind is stored in this
+  // SinglePageDecodeCache.
+  bool contains(const Instruction* inst) {
+    return pageStart_ == PageStart(inst);
+  }
+  void clearDecode(const Instruction* inst) {
+    uintptr_t offset = (uintptr_t(inst) & PageMask) / InstSize;
+    decodeCache_[offset] = InstDecodedKind::NotDecodedYet;
+  }
+  InstDecodedKind* decodePtr(const Instruction* inst) {
+    uintptr_t offset = (uintptr_t(inst) & PageMask) / InstSize;
+    uint32_t instValue = *reinterpret_cast<const uint32_t*>(inst);
+    instCache_[offset] = instValue;
+    return &decodeCache_[offset];
+  }
+  InstDecodedKind decode(const Instruction* inst) const {
+    uintptr_t offset = (uintptr_t(inst) & PageMask) / InstSize;
+    InstDecodedKind val = decodeCache_[offset];
+    uint32_t instValue = *reinterpret_cast<const uint32_t*>(inst);
+    MOZ_ASSERT_IF(val != InstDecodedKind::NotDecodedYet,
+                  instCache_[offset] == instValue);
+    return val;
+  }
+
+ private:
+  // Record the address at which the corresponding code page starts.
+  const uintptr_t pageStart_;
+
+  // Cache what instruction got decoded previously, in order to assert if we see
+  // any stale instructions after.
+  uint32_t instCache_[InstPerPage];
+
+  // Cache the decoding of the instruction such that we can skip the decoding
+  // part.
+  InstDecodedKind decodeCache_[InstPerPage];
+};
+
+// A DecoderVisitor which will record which visitor function should be called
+// the next time we want to decode the same instruction.
+class CachingDecoderVisitor : public DecoderVisitor {
+ public:
+  CachingDecoderVisitor() = default;
+  virtual ~CachingDecoderVisitor() {}
+
+#define DECLARE(A) virtual void Visit##A(const Instruction* instr) { \
+    if (last_) { \
+      MOZ_ASSERT(*last_ == InstDecodedKind::NotDecodedYet); \
+      *last_ = InstDecodedKind::A; \
+      last_ = nullptr; \
+    } \
+  };
+
+  VISITOR_LIST(DECLARE)
+#undef DECLARE
+
+  void setDecodePtr(InstDecodedKind* ptr) {
+    last_ = ptr;
+  }
+
+ private:
+  InstDecodedKind* last_;
+};
+
+// The Caching decoder works by extending the default vixl Decoder class. It
+// extends it by overloading the Decode function.
+//
+// The overloaded Decode function checks whether the instruction given as
+// argument got decoded before or since it got invalidated. If it was not
+// previously decoded, the value of the instruction is recorded as well as the
+// kind of instruction. Otherwise, the value of the instruction is checked
+// against the previously recorded value and the instruction kind is used to
+// skip the decoding visitor and resume the execution of instruction.
+//
+// The caching decoder stores the equivalent of a page of executable code in a
+// hash-table. Each SinglePageDecodeCache stores an array of decoded kind as
+// well as the value of the previously decoded instruction.
+//
+// When testing if an instruction was decoded before, we check if the address of
+// the instruction is contained in the last SinglePageDecodeCache. If it is not,
+// then the hash-table entry is queried and created if necessary, and the last
+// SinglePageDecodeCache is updated. Then, the last SinglePageDecodeCache
+// necessary contains the decoded kind of the instruction given as argument.
+//
+// The caching decoder add an extra function for flushing the cache, which is in
+// charge of clearing the decoded kind of instruction in the range of addresses
+// given as argument. This is indirectly called by
+// CPU::EnsureIAndDCacheCoherency.
+class CachingDecoder : public Decoder {
+  using ICacheMap = mozilla::HashMap<uintptr_t, SinglePageDecodeCache*>;
+ public:
+  CachingDecoder()
+      : lastPage_(nullptr)
+  {
+    PrependVisitor(&cachingDecoder_);
+  }
+  ~CachingDecoder() {
+    RemoveVisitor(&cachingDecoder_);
+  }
+
+  void Decode(const Instruction* instr);
+  void Decode(Instruction* instr) {
+    Decode(const_cast<const Instruction*>(instr));
+  }
+
+  void FlushICache(void* start, size_t size);
+
+ private:
+  // Record the type of the decoded instruction, to avoid decoding it a second
+  // time the next time we execute it.
+  CachingDecoderVisitor cachingDecoder_;
+
+  // Store the mapping of Instruction pointer to the corresponding
+  // SinglePageDecodeCache.
+  ICacheMap iCache_;
+
+  // Record the last SinglePageDecodeCache seen, such that we can quickly access
+  // it for the next instruction.
+  SinglePageDecodeCache* lastPage_;
+};
+
+}
+#endif // !JS_CACHE_SIMULATOR_ARM64
+#endif // !VIXL_A64_MOZ_CACHING_DECODER_A64_H_