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

lib/compiler/implementation/ssa/codegen.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class SsaCodeGeneratorTask extends CompilerTask {
   final JavaScriptBackend backend;
   SsaCodeGeneratorTask(JavaScriptBackend backend)
       : this.backend = backend,
         super(backend.compiler);
   String get name() => 'SSA code generator';
@@ skipping 1213 matching lines @@
       visitInvokeUnary(node, op);
       buffer.add(' >>> 0');
       this.expectedPrecedence = oldPrecedence;
       endExpression(unsignedShiftPrecedences.precedence);
     } else {
       visitInvokeUnary(node, op);
     }
   }
 
   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(right, JSPrecedence.EQUALITY_PRECEDENCE);
+          buffer.add(' == null');
+          endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
+          buffer.add(" : ");
           beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
           use(left, JSPrecedence.EQUALITY_PRECEDENCE);
-          buffer.add(' == null');
+          buffer.add(' === ');
+          use(right, JSPrecedence.EQUALITY_PRECEDENCE);
           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);
-          });
         });
-      }
-    } else {
-      beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
-      use(left, JSPrecedence.EQUALITY_PRECEDENCE);
-      buffer.add(' === ');
-      use(right, JSPrecedence.RELATIONAL_PRECEDENCE);
-      endExpression(JSPrecedence.EQUALITY_PRECEDENCE);
+      });
     }
   }
 
   visitEquals(HEquals node) {
     if (node.builtin) {
       emitIdentityComparison(node.left, node.right);
     } else {
       visitInvokeStatic(node);
     }
   }
@@ skipping 1825 matching lines @@
       startBailoutSwitch();
     }
   }
 
   void endLabeledBlock(HLabeledBlockInformation labeledBlockInfo) {
     if (labeledBlockInfo.body.start.hasGuards()) {
       endBailoutSwitch();
     }
   }
 }
+
+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 '===';
+  }
+}