diff --git a/implementation-contributed/v8/mjsunit/compiler/int64.js b/implementation-contributed/v8/mjsunit/compiler/int64.js
new file mode 100644
index 0000000000..0a88a95895
--- /dev/null
+++ b/implementation-contributed/v8/mjsunit/compiler/int64.js
@@ -0,0 +1,91 @@
+// 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.
+
+// Flags: --allow-natives-syntax
+
+// Test NumberAdd with PositiveSafeInteger -> PositiveSafeInteger (as Tagged).
+(function() {
+  function foo(x) {
+    const i = x ? 0xFFFFFFFF : 0;
+    return i + 1;
+  }
+
+  assertEquals(0x000000001, foo(false));
+  assertEquals(0x000000001, foo(false));
+  assertEquals(0x100000000, foo(true));
+  assertEquals(0x100000000, foo(true));
+  %OptimizeFunctionOnNextCall(foo);
+  assertEquals(0x000000001, foo(false));
+  assertEquals(0x100000000, foo(true));
+})();
+
+// Test NumberAdd with SafeInteger -> SafeInteger (as Tagged).
+(function() {
+  function foo(x) {
+    const i = x ? 0xFFFFFFFF : -1;
+    return i + 1;
+  }
+
+  assertEquals(0x000000000, foo(false));
+  assertEquals(0x000000000, foo(false));
+  assertEquals(0x100000000, foo(true));
+  assertEquals(0x100000000, foo(true));
+  %OptimizeFunctionOnNextCall(foo);
+  assertEquals(0x000000000, foo(false));
+  assertEquals(0x100000000, foo(true));
+})();
+
+// NumberAdd: Smi x Unsigned32 -> SafeInteger (as Float64).
+(function() {
+  const a = new Float64Array(1);
+
+  function foo(o) {
+    a[0] = o.x + 0xFFFFFFFF;
+    return a[0];
+  }
+
+  assertEquals(0x0FFFFFFFF, foo({x:0}));
+  assertEquals(0x100000000, foo({x:1}));
+  %OptimizeFunctionOnNextCall(foo);
+  assertEquals(0x100000000, foo({x:1}));
+})();
+
+// NumberAdd: Smi x Unsigned32 -> SafeInteger (as TaggedSigned).
+(function() {
+  function foo(o) {
+    return {x: Math.floor((o.x + 11123456789) + -11123456788)}.x;
+  }
+
+  assertEquals(1, foo({x:0}));
+  assertEquals(2, foo({x:1}));
+  %OptimizeFunctionOnNextCall(foo);
+  assertEquals(2, foo({x:1}));
+})();
+
+// NumberSubtract: Unsigned32 x Unsigned32 -> SafeInteger (as Word32).
+(function() {
+  function foo(a, i) {
+    i = ((i >>> 0)) - 0xFFFFFFFF;
+    return a[i];
+  }
+
+  assertEquals(1, foo([1], 0xFFFFFFFF));
+  assertEquals(2, foo([2], 0xFFFFFFFF));
+  %OptimizeFunctionOnNextCall(foo);
+  assertEquals(3, foo([3], 0xFFFFFFFF));
+})();
+
+// Test that the Deoptimizer can handle Word64 properly.
+(function() {
+  function foo(b) {
+    const i = ((b >>> 0)) - 0xFFFFFFFF;
+    %DeoptimizeFunction(foo);
+    return i;
+  }
+
+  assertEquals(0, foo(0xFFFFFFFF));
+  assertEquals(0, foo(0xFFFFFFFF));
+  %OptimizeFunctionOnNextCall(foo);
+  assertEquals(0, foo(0xFFFFFFFF));
+})();
diff --git a/implementation-contributed/v8/mjsunit/compiler/number-add.js b/implementation-contributed/v8/mjsunit/compiler/number-add.js
new file mode 100644
index 0000000000..d0f2c63194
--- /dev/null
+++ b/implementation-contributed/v8/mjsunit/compiler/number-add.js
@@ -0,0 +1,33 @@
+// 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.
+
+// Flags: --allow-natives-syntax
+
+// This tests that NumberAdd passes on the right truncations
+// even if it figures out during SimplifiedLowering that it
+// can indeed do a Word32 operation (based on the feedback
+// baked in for its inputs by other operators).
+(function() {
+  // We need a + with Number feedback to get to a NumberAdd
+  // during the typed lowering pass of TurboFan's frontend.
+  function foo(x, y) { return x + y; }
+  foo(0.1, 0.2);
+  foo(0.1, 0.2);
+
+  // Now we need to fool TurboFan to think that it has to
+  // perform the `foo(x,-1)` on Float64 values until the
+  // very last moment (after the RETYPE phase of the
+  // SimplifiedLowering) where it realizes that the inputs
+  // and outputs of the NumberAdd allow it perform the
+  // operation on Word32.
+  function bar(x) {
+    x = Math.trunc(foo(x - 1, 1));
+    return foo(x, -1);
+  }
+
+  assertEquals(0, bar(1));
+  assertEquals(1, bar(2));
+  %OptimizeFunctionOnNextCall(bar);
+  assertEquals(2, bar(3));
+})();