[turbofan] Optimize certain chains of Branch into a Switch.

test/mjsunit/asm/switch.js

+// Copyright 2015 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.
+
+var stdlib = this;
+var foreign = {};
+var heap = new ArrayBuffer(64 * 1024);
+
+
+var switch1 = (function(stdlib, foreign, heap) {
+  "use asm";
+  function switch1(i) {
+    i = i|0;
+    switch (i) {
+      case 0: return 1;
+      case 1: return 2;
+      default: return i|0;
+    }
+  }
+  return { switch1: switch1 };
+})(stdlib, foreign, heap).switch1;
+
+assertEquals(1, switch1(0));
+assertEquals(2, switch1(1));
+for (var i = -2147483648; i < 2147483648; i += 3999773) {
+  assertEquals(i, switch1(i));
+}
+
+
+var switch2 = (function(stdlib, foreign, heap) {
+  "use asm";
+  function switch2(i) {
+    i = i|0;
+    var j = 0;
+    switch (i) {
+      case 0: j = 1; break;
+      case 1: j = 2; break;
+      case 2: j = 3; break;
+      default: j = i|0; break;
+    }
+    return j|0;
+  }
+  return { switch2: switch2 };
+})(stdlib, foreign, heap).switch2;
+
+assertEquals(1, switch2(0));
+assertEquals(2, switch2(1));
+assertEquals(3, switch2(2));
+for (var i = -2147483648; i < 2147483648; i += 3999773) {
+  assertEquals(i, switch2(i));
+}
+
+
+var switch3 = (function(stdlib, foreign, heap) {
+  "use asm";
+  function switch3(i) {
+    i = i|0;
+    var j = 0;
+    switch (i) {
+      case 0:
+      case 1: j = 1; break;
+      case 2:
+      case 3: j = 2; break;
+      case 4:
+      case 5: j = 3; break;
+      default: j = 0; break;
+    }
+    return j|0;
+  }
+  return { switch3: switch3 };
+})(stdlib, foreign, heap).switch3;
+
+assertEquals(1, switch3(0));
+assertEquals(1, switch3(1));
+assertEquals(2, switch3(2));
+assertEquals(2, switch3(3));
+assertEquals(3, switch3(4));
+assertEquals(3, switch3(5));
+for (var i = -2147483648; i < 2147483648; i += 3999773) {
+  assertEquals(0, switch3(i));
+}
+
+
+var switch4 = (function(stdlib, foreign, heap) {
+  "use asm";
+  function switch4(i) {
+    i = i|0;
+    switch (i) {
+      case -1:
+      case 1:
+        return 0;
+
+      case -2:
+      case 2:
+        return 1;
+
+      case -3:
+      case 3:
+        return 2;
+
+      case -8:
+      case 8:
+        return 3;
+
+      default:
+        return 4;
+    }
+  }
+  return { switch4: switch4 };
+})(stdlib, foreign, heap).switch4;
+
+assertEquals(4, switch4(0));
+assertEquals(0, switch4(-1));
+assertEquals(0, switch4(1));
+assertEquals(1, switch4(-2));
+assertEquals(1, switch4(2));
+assertEquals(3, switch4(-8));
+assertEquals(3, switch4(8));
+assertEquals(4, switch4(-123456789));
+assertEquals(4, switch4(123456789));