Redo "dart2js: Redo known-type analysis after load-elimination"

pkg/compiler/lib/src/ssa/codegen.dart

Index: pkg/compiler/lib/src/ssa/codegen.dart
diff --git a/pkg/compiler/lib/src/ssa/codegen.dart b/pkg/compiler/lib/src/ssa/codegen.dart
index f4223405bb4df74c5eb43bc6a0f00150a6d29bea..27fc2e879e9cda61e0f55d0e6d80615f142c566d 100644
--- a/pkg/compiler/lib/src/ssa/codegen.dart
+++ b/pkg/compiler/lib/src/ssa/codegen.dart
@@ -2849,11 +2849,6 @@ class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
 
   void visitTypeConversion(HTypeConversion node) {
     if (node.isArgumentTypeCheck || node.isReceiverTypeCheck) {
-      // An int check if the input is not int or null, is not
-      // sufficient for doing an argument or receiver check.

[sra1, 2017/02/01 00:59:15]

I think this is incorrect. The check is Math.floor(x) !== x, which will not
accidentally accept numeric strings.

[Siggi Cherem (dart-lang), 2017/02/01 01:31:48]

Could we end up hitting the Math.floor case when the input is `null`? which will
say true instead of false? for example if input.isPrimitiveOrNull? 

I'm not as familiar with this as you are, so feel free to ignore and I'll ask
you in person later in the week.

[sra1, 2017/02/01 02:15:46]

It works as intended:

  Math.floor(null) --> 0,           0 !== null
  Math.floor(undefined) --> NaN,  NaN !== undefined

These cases might be a slow path, but only when the program is going to throw an
exception.
`x is int` sometimes generates an additional `typeof x === "number"` to avoid
this potential slowness.

-      assert(compiler.options.trustTypeAnnotations ||
-          !node.checkedType.containsOnlyInt(closedWorld) ||
-          node.checkedInput.isIntegerOrNull(closedWorld));
       js.Expression test = generateReceiverOrArgumentTypeTest(
           node.checkedInput, node.checkedType);
       js.Block oldContainer = currentContainer;