diff --git a/Source/JavaScriptCore/ChangeLog b/Source/JavaScriptCore/ChangeLog
index 54e88de61f00..f8452c0b0e38 100644
--- a/Source/JavaScriptCore/ChangeLog
+++ b/Source/JavaScriptCore/ChangeLog
@@ -1,3 +1,21 @@
+2017-08-09  Caio Lima  <ticaiolima@gmail.com>
+
+        [JSC] Create JSSet constructor that accepts it's size as parameter
+        https://bugs.webkit.org/show_bug.cgi?id=173297
+
+        Reviewed by Saam Barati.
+
+        This patch is adding a new constructor to JSSet that gives its
+        expected initial size. It is important to avoid re-hashing and mutiple
+        allocations when we know the final size of JSSet, such as in
+        CodeBlock::setConstantIdentifierSetRegisters.
+
+        * bytecode/CodeBlock.cpp:
+        (JSC::CodeBlock::setConstantIdentifierSetRegisters):
+        * runtime/HashMapImpl.h:
+        (JSC::HashMapImpl::HashMapImpl):
+        * runtime/JSSet.h:
+
 2017-08-09  Caitlin Potter  <caitp@igalia.com>
 
         Early error on ANY operator before new.target
diff --git a/Source/JavaScriptCore/bytecode/CodeBlock.cpp b/Source/JavaScriptCore/bytecode/CodeBlock.cpp
index 28ee727d6c8c..e123ff8f09f8 100644
--- a/Source/JavaScriptCore/bytecode/CodeBlock.cpp
+++ b/Source/JavaScriptCore/bytecode/CodeBlock.cpp
@@ -877,12 +877,13 @@ void CodeBlock::setConstantIdentifierSetRegisters(VM& vm, const Vector<ConstantI
     ExecState* exec = globalObject->globalExec();
 
     for (const auto& entry : constants) {
+        const IdentifierSet& set = entry.first;
+
         Structure* setStructure = globalObject->setStructure();
         RETURN_IF_EXCEPTION(scope, void());
-        JSSet* jsSet = JSSet::create(exec, vm, setStructure);
+        JSSet* jsSet = JSSet::create(exec, vm, setStructure, set.size());
         RETURN_IF_EXCEPTION(scope, void());
 
-        const IdentifierSet& set = entry.first;
         for (auto setEntry : set) {
             JSString* jsString = jsOwnedString(&vm, setEntry.get()); 
             jsSet->add(exec, jsString);
diff --git a/Source/JavaScriptCore/runtime/HashMapImpl.h b/Source/JavaScriptCore/runtime/HashMapImpl.h
index d18717671335..2908a10bc81a 100644
--- a/Source/JavaScriptCore/runtime/HashMapImpl.h
+++ b/Source/JavaScriptCore/runtime/HashMapImpl.h
@@ -300,6 +300,16 @@ class HashMapImpl : public JSNonFinalObject {
     {
     }
 
+    HashMapImpl(VM& vm, Structure* structure, uint32_t sizeHint)
+        : Base(vm, structure)
+        , m_keyCount(0)
+        , m_deleteCount(0)
+    {
+        uint32_t capacity = ((Checked<uint32_t>(sizeHint) * 2) + 1).unsafeGet();
+        capacity = std::max<uint32_t>(WTF::roundUpToPowerOfTwo(capacity), 4U);
+        m_capacity = capacity;
+    }
+
     ALWAYS_INLINE HashMapBucketType** buffer() const
     {
         return m_buffer->buffer();
diff --git a/Source/JavaScriptCore/runtime/JSSet.h b/Source/JavaScriptCore/runtime/JSSet.h
index e6764079e28f..4283293ea529 100644
--- a/Source/JavaScriptCore/runtime/JSSet.h
+++ b/Source/JavaScriptCore/runtime/JSSet.h
@@ -47,7 +47,12 @@ class JSSet final : public HashMapImpl<HashMapBucket<HashMapBucketDataKey>> {
 
     static JSSet* create(ExecState* exec, VM& vm, Structure* structure)
     {
-        JSSet* instance = new (NotNull, allocateCell<JSSet>(vm.heap)) JSSet(vm, structure);
+        return create(exec, vm, structure, 0);
+    }
+
+    static JSSet* create(ExecState* exec, VM& vm, Structure* structure, uint32_t size)
+    {
+        JSSet* instance = new (NotNull, allocateCell<JSSet>(vm.heap)) JSSet(vm, structure, size);
         instance->finishCreation(exec, vm);
         return instance;
     }
@@ -62,6 +67,11 @@ class JSSet final : public HashMapImpl<HashMapBucket<HashMapBucketDataKey>> {
     {
     }
 
+    JSSet(VM& vm, Structure* structure, uint32_t sizeHint)
+        : Base(vm, structure, sizeHint)
+    {
+    }
+
     static String toStringName(const JSObject*, ExecState*);
 };