[turbofan] Only infer signedness for Float64->Word32 representation change from the input type.

test/mjsunit/compiler/regress-f64-w32-change.js

Index: test/mjsunit/compiler/regress-f64-w32-change.js
diff --git a/test/mjsunit/regress/regress-crbug-500824.js b/test/mjsunit/compiler/regress-f64-w32-change.js
similarity index 51%
copy from test/mjsunit/regress/regress-crbug-500824.js
copy to test/mjsunit/compiler/regress-f64-w32-change.js
index 08d0d107cad78c876d6f92e30c9159c3bb10d76a..834da290e09ff348cfebd3ffb27d6ba1a20a6c4d 100644
--- a/test/mjsunit/regress/regress-crbug-500824.js
+++ b/test/mjsunit/compiler/regress-f64-w32-change.js
@@ -4,20 +4,20 @@
 
 // Flags: --allow-natives-syntax
 
-function get_thrower() {
-  "use strict";
-  return Object.getOwnPropertyDescriptor(arguments, "callee").get;
-}
-
-var f = (function(v) {
+var f = (function () {
   "use asm";
-  function fun() {
-    switch (v) {}
+  var f64use = 0;
+  function f(x, b) {
+    x = x|0;
+    b = b >>> 0;
+    var f64 = x ? -1 : b;
+    f64use = f64 + 0.5;
+    var w32 = x ? 1 : f64;
+    return (w32 + 1)|0;
   }
-  return {
-    fun: fun
-  };
-})(get_thrower()).fun;
+
+  return f;
+})();
 
 %OptimizeFunctionOnNextCall(f);
-f();
+assertEquals(0, f(0, -1));