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

lib/compiler/implementation/ssa/codegen_helpers.dart

Index: lib/compiler/implementation/ssa/codegen_helpers.dart
diff --git a/lib/compiler/implementation/ssa/codegen_helpers.dart b/lib/compiler/implementation/ssa/codegen_helpers.dart
index 4344721da0b14d7f8ad8f767a296dbf9ed10fc3e..0659f46db9ef31cee7fc2aeb8853d25326a1a1a2 100644
--- a/lib/compiler/implementation/ssa/codegen_helpers.dart
+++ b/lib/compiler/implementation/ssa/codegen_helpers.dart
@@ -52,16 +52,26 @@ class SsaInstructionMerger extends HBaseVisitor {
   // 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).
+  // If an equality operation is builtin it must only have its inputs generated
+  // at use site if it does not require an expression with repeated uses
+  // (because of null / undefined).
   void visitEquals(HEquals instruction) {
     if (!instruction.builtin) super.visitEquals(instruction);
-    // Otherwise do nothing.
+    if (singleIdentityComparison(instruction.left, instruction.right) != null) {
+      super.visitEquals(instruction);
+    }
+    // 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) {}
+  // An identity operation must only have its inputs generated at use site if
+  // does not require an expression with multiple uses (because of null /
+  // undefined).
+  void visitIdentity(HIdentity instruction) {
+    if (singleIdentityComparison(instruction.left, instruction.right) != null) {
+      super.visitIdentity(instruction);
+    }
+    // Do nothing.
+  }
 
   void visitTypeConversion(HTypeConversion instruction) {
     if (!instruction.isChecked) {