Make undefined and null equivalent.

lib/compiler/implementation/ssa/codegen_helpers.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.
 
 /**
  * Instead of emitting each SSA instruction with a temporary variable
  * mark instructions that can be emitted at their use-site.
  * For example, in:
  *   t0 = 4;
  *   t1 = 3;
@@ skipping 21 matching lines @@
           && input is !HPhi) {
         expectedInputs.add(input);
       }
     }
   }
 
   // The codegen might use the input multiple times, so it must not be
   // set generate at use site.
   void visitIs(HIs instruction) {}
 
-  // A check method must not have its input generate at use site,
+  // A check method must not have its input generated at use site,
   // because it's using it multiple times.
   void visitCheck(HCheck instruction) {}
 
   // A type guard should not generate its input at use site, otherwise
   // they would not be alive.
   void visitTypeGuard(HTypeGuard instruction) {}
 
+  // If an equality operation is builtin it must not have its input generated at
+  // use site, because it's using it multiple times (because of null/undefined).
+  void visitEquals(HEquals instruction) {
+    if (!instruction.builtin) super.visitEquals(instruction);
+    // Otherwise do nothing.
+  }
+
+  // Identity operations must not have its input generated at use site, because
+  // it's using it multiple times (because of null/undefined).
+  void visitIdentity(HIdentity instruction) {}
+
   void visitTypeConversion(HTypeConversion instruction) {
     if (!instruction.isChecked()) {
       generateAtUseSite.add(instruction);
     } else if (instruction.isCheckedModeCheck()) {
       // Checked mode checks compile to code that only use their input
       // once, so we can safely visit them and try to merge the input.
       visitInstruction(instruction);
     }
   }
 
@@ skipping 154 matching lines @@
 
     if (hasAnyStatement(elseBlock, elseInput)) return;
     assert(elseBlock.successors.length == 1);
     assert(end.predecessors.length == 2);
 
     HBasicBlock thenBlock = startIf.thenBlock;
     // Skip trivial goto blocks.
     while (thenBlock.successors[0] != end && thenBlock.first is HGoto) {
       thenBlock = thenBlock.successors[0];
     }
-    
+
     // If the [thenBlock] is already a control flow operation, and does not
     // have any statement and its join block is [end], we can emit a
     // sequence of control flow operation.
     if (controlFlowOperators.contains(thenBlock.last)) {
       HIf otherIf = thenBlock.last;
       if (otherIf.joinBlock !== end) return;
       if (hasAnyStatement(thenBlock, otherIf)) return;
     } else {
       if (end.predecessors[0] !== thenBlock) return;
       if (hasAnyStatement(thenBlock, thenInput)) return;
       assert(thenBlock.successors.length == 1);
     }
-     
+
     // From now on, we have recognized a control flow operation built from
     // the builder. Mark the if instruction as such.
     controlFlowOperators.add(startIf);
 
     // If the operation is only used by the first instruction
     // of its block and is safe to be generated at use sute, mark it
     // so.
     if (phi.usedBy.length == 1
         && phi.usedBy[0] === phi.block.first
         && isSafeToGenerateAtUseSite(phi.usedBy[0], phi)) {
@@ skipping 87 matching lines @@
   };
 }
 
 class JSBinaryOperatorPrecedence {
   final int left;
   final int right;
   const JSBinaryOperatorPrecedence(this.left, this.right);
   // All binary operators (excluding assignment) are left associative.
   int get precedence() => left;
 }