[turbofan] add regression test for chromium:796041

The missing regression test for
https://chromium-review.googlesource.com/c/v8/v8/+/847011

Bug: chromium:796041
Change-Id: I3d791d6485221d2fa68def2c7be96c48822aa651
Reviewed-on: https://chromium-review.googlesource.com/848995
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50349}

test/mjsunit/compiler/regress-796041.js

@@ -0,0 +1,35 @@
+// 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
+
+'use strict';
+
+function f(abort, n, a, b) {
+  if (abort) return;
+  var x = a ? true : "" + a;
+  if (!a) {
+    var dead = n + 1 + 1;
+    if(!b) {
+      x = dead;
+    }
+    if (x) {
+      x = false;
+    }
+    if (b) {
+      x = false;
+    }
+  }
+  return x + 1;
+}
+f(false, 5); f(false, 6); f(false, 7); f(false, 8);
+
+function g(abort, a, b) {
+  return f(abort, "abc", a, b);
+}
+
+g(true); g(true); g(true); g(true);
+
+%OptimizeFunctionOnNextCall(g);
+g(false);