Implement TDZ in StoreIC for top-level lexicals.

StoreIC::Store was missing a check present in LoadIC::Load.

R=rossberg@chromium.org
BUG=v8:3941
LOG=Y

Review URL: https://codereview.chromium.org/1001323002

Cr-Commit-Position: refs/heads/master@{#27182}

src/hydrogen.cc

@@ -5327,7 +5327,7 @@ void HOptimizedGraphBuilder::VisitVariableProxy(VariableProxy* expr) {
           Handle<Context> script_context = ScriptContextTable::GetContext(
               script_contexts, lookup.context_index);
           Handle<Object> current_value =
-              FixedArray::get(script_context, lookup.context_index);
+              FixedArray::get(script_context, lookup.slot_index);
 
           // If the values is not the hole, it will stay initialized,
           // so no need to generate a check.
@@ -6488,6 +6488,16 @@ void HOptimizedGraphBuilder::HandleGlobalVariableAssignment(
       }
       Handle<Context> script_context =
           ScriptContextTable::GetContext(script_contexts, lookup.context_index);
+
+      Handle<Object> current_value =
+          FixedArray::get(script_context, lookup.slot_index);
+
+      // If the values is not the hole, it will stay initialized,
+      // so no need to generate a check.
+      if (*current_value == *isolate()->factory()->the_hole_value()) {
+        return Bailout(kReferenceToUninitializedVariable);
+      }
+
       HStoreNamedField* instr = Add<HStoreNamedField>(
           Add<HConstant>(script_context),
           HObjectAccess::ForContextSlot(lookup.slot_index), value);

src/ic/ic.cc

@@ -1558,6 +1558,15 @@ MaybeHandle<Object> StoreIC::Store(Handle<Object> object, Handle<Name> name,
         return TypeError("const_assign", object, name);
       }
 
+      Handle<Object> previous_value =
+          FixedArray::get(script_context, lookup_result.slot_index);
+
+      if (*previous_value == *isolate()->factory()->the_hole_value()) {
+        // Do not install stubs and stay pre-monomorphic for
+        // uninitialized accesses.
+        return ReferenceError("not_defined", name);
+      }
+
       if (FLAG_use_ic &&
           StoreScriptContextFieldStub::Accepted(&lookup_result)) {
         StoreScriptContextFieldStub stub(isolate(), &lookup_result);

test/cctest/test-decls.cc

@@ -1183,3 +1183,87 @@ TEST(Regress425510) {
     }
   }
 }
+
+
+TEST(Regress3941) {
+  i::FLAG_harmony_scoping = true;
+  i::FLAG_allow_natives_syntax = true;
+
+  HandleScope handle_scope(CcTest::isolate());
+
+  {
+    SimpleContext context;
+    context.Check("function f() { x = 1; }", EXPECT_RESULT,
+                  Undefined(CcTest::isolate()));
+    context.Check("'use strict'; f(); let x = 2; x", EXPECT_EXCEPTION);
+  }
+
+
+  {
+    // Train ICs.
+    SimpleContext context;
+    context.Check("function f() { x = 1; }", EXPECT_RESULT,
+                  Undefined(CcTest::isolate()));
+    for (int i = 0; i < 4; i++) {
+      context.Check("f(); x", EXPECT_RESULT, Number::New(CcTest::isolate(), 1));
+    }
+    context.Check("'use strict'; f(); let x = 2; x", EXPECT_EXCEPTION);
+  }
+
+
+  {
+    // Optimize.
+    SimpleContext context;
+    context.Check("function f() { x = 1; }", EXPECT_RESULT,
+                  Undefined(CcTest::isolate()));
+    for (int i = 0; i < 4; i++) {
+      context.Check("f(); x", EXPECT_RESULT, Number::New(CcTest::isolate(), 1));
+    }
+    context.Check("%OptimizeFunctionOnNextCall(f); f(); x", EXPECT_RESULT,
+                  Number::New(CcTest::isolate(), 1));
+
+    context.Check("'use strict'; f(); let x = 2; x", EXPECT_EXCEPTION);
+  }
+}
+
+
+TEST(Regress3941_Reads) {
+  i::FLAG_harmony_scoping = true;
+  i::FLAG_allow_natives_syntax = true;
+
+  HandleScope handle_scope(CcTest::isolate());
+
+  {
+    SimpleContext context;
+    context.Check("function f() { return x; }", EXPECT_RESULT,
+                  Undefined(CcTest::isolate()));
+    context.Check("'use strict'; f(); let x = 2; x", EXPECT_EXCEPTION);
+  }
+
+
+  {
+    // Train ICs.
+    SimpleContext context;
+    context.Check("function f() { return x; }", EXPECT_RESULT,
+                  Undefined(CcTest::isolate()));
+    for (int i = 0; i < 4; i++) {
+      context.Check("f()", EXPECT_EXCEPTION);
+    }
+    context.Check("'use strict'; f(); let x = 2; x", EXPECT_EXCEPTION);
+  }
+
+
+  {
+    // Optimize.
+    SimpleContext context;
+    context.Check("function f() { return x; }", EXPECT_RESULT,
+                  Undefined(CcTest::isolate()));
+    for (int i = 0; i < 4; i++) {
+      context.Check("f()", EXPECT_EXCEPTION);
+    }
+    context.Check("%OptimizeFunctionOnNextCall(f);", EXPECT_RESULT,
+                  Undefined(CcTest::isolate()));
+
+    context.Check("'use strict'; f(); let x = 2; x", EXPECT_EXCEPTION);
+  }
+}