Allow === and == to generate inputs at the use site when compiling to a single comparison

lib/compiler/implementation/ssa/codegen.dart

Index: lib/compiler/implementation/ssa/codegen.dart
diff --git a/lib/compiler/implementation/ssa/codegen.dart b/lib/compiler/implementation/ssa/codegen.dart
index 3b798e90166f124ae332d6251f5e0601ceea7300..2ad7d60177420fa375dcc6a9a87284d486efcba4 100644
--- a/lib/compiler/implementation/ssa/codegen.dart
+++ b/lib/compiler/implementation/ssa/codegen.dart
@@ -1231,45 +1231,35 @@ class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
   }
 
   void emitIdentityComparison(HInstruction left, HInstruction right) {
-    HType leftType = left.propagatedType;
-    HType rightType = right.propagatedType;
-    if (leftType.canBeNull() && rightType.canBeNull()) {
-      if (left.isConstantNull() || right.isConstantNull() ||
-          (leftType.isPrimitive() && leftType == rightType)) {
+    String op = singleIdentityComparison(left, right);
+    if (op != null) {
+      beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
+      use(left, JSPrecedence.EQUALITY_PRECEDENCE);
+      buffer.add(' $op ');
+      use(right, JSPrecedence.RELATIONAL_PRECEDENCE);
+      endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
+    } else {
+      assert(NullConstant.JsNull == 'null');
+      withPrecedence(JSPrecedence.CONDITIONAL_PRECEDENCE, () {
         beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
         use(left, JSPrecedence.EQUALITY_PRECEDENCE);
-        buffer.add(' == ');
-        use(right, JSPrecedence.RELATIONAL_PRECEDENCE);
+        buffer.add(' == null');
         endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-      } else {
-        assert(NullConstant.JsNull == 'null');
-        withPrecedence(JSPrecedence.CONDITIONAL_PRECEDENCE, () {
+        buffer.add(' ? ');
+        this.expectedPrecedence = JSPrecedence.ASSIGNMENT_PRECEDENCE;
+        withPrecedence(JSPrecedence.LOGICAL_AND_PRECEDENCE, () {
           beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-          use(left, JSPrecedence.EQUALITY_PRECEDENCE);
+          use(right, JSPrecedence.EQUALITY_PRECEDENCE);
           buffer.add(' == null');
           endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-          buffer.add(' ? ');
-          this.expectedPrecedence = JSPrecedence.ASSIGNMENT_PRECEDENCE;
-          withPrecedence(JSPrecedence.LOGICAL_AND_PRECEDENCE, () {
-            beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-            use(right, JSPrecedence.EQUALITY_PRECEDENCE);
-            buffer.add(' == null');
-            endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-            buffer.add(" : ");
-            beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-            use(left, JSPrecedence.EQUALITY_PRECEDENCE);
-            buffer.add(' === ');
-            use(right, JSPrecedence.EQUALITY_PRECEDENCE);
-            endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-          });
+          buffer.add(" : ");
+          beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
+          use(left, JSPrecedence.EQUALITY_PRECEDENCE);
+          buffer.add(' === ');
+          use(right, JSPrecedence.EQUALITY_PRECEDENCE);
+          endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
         });
-      }
-    } else {
-      beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-      use(left, JSPrecedence.EQUALITY_PRECEDENCE);
-      buffer.add(' === ');
-      use(right, JSPrecedence.RELATIONAL_PRECEDENCE);
-      endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
+      });
     }
   }
 
@@ -3115,3 +3105,19 @@ class SsaUnoptimizedCodeGenerator extends SsaCodeGenerator {
     }
   }
 }
+
+String singleIdentityComparison(HInstruction left, HInstruction right) {
+  // Returns the single identity comparison (== or ===) or null if a more
+  // complex expression is required.
+  HType leftType = left.propagatedType;
+  HType rightType = right.propagatedType;
+  if (leftType.canBeNull() && rightType.canBeNull()) {
+    if (left.isConstantNull() || right.isConstantNull() ||
+        (leftType.isPrimitive() && leftType == rightType)) {
+      return '==';
+    }
+    return null;
+  } else {
+    return '===';
+  }
+}