Crankshaft: Recognize (i >>> 0) === i for integer32 inputs and replace

src/hydrogen.cc

Index: src/hydrogen.cc
===================================================================
--- src/hydrogen.cc	(revision 14364)
+++ src/hydrogen.cc	(working copy)
@@ -10041,6 +10041,21 @@
 }
 
 
+void HOptimizedGraphBuilder::HandleTripleShiftZeroCompare(
+    CompareOperation* expr,
+    HValue* input) {
+  // (i >>> 0) === i is transformed to i >= 0.
+  // (i >>> 0) !== i is transformed to i < 0.
+  Token::Value op = (expr->op() == Token::EQ_STRICT) ? Token::GTE : Token::LT;
+  HCompareIDAndBranch* compare =
+      new(zone()) HCompareIDAndBranch(input, graph()->GetConstant0(), op);
+  compare->set_observed_input_representation(Representation::Integer32(),
+                                             Representation::Integer32());
+  compare->set_position(expr->position());
+  return ast_context()->ReturnControl(compare, expr->id());
+}
+
+
 void HOptimizedGraphBuilder::HandleLiteralCompareTypeof(CompareOperation* expr,
                                                         HTypeof* typeof_expr,
                                                         Handle<String> check) {