dart2js: Constant fold num.round()

pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart

Index: pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart
diff --git a/pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart b/pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart
index 463c31cfcd2009aff40c5abe25a0efda59d616c4..8bcca400dc94960fa7d885c62b801651f2c6362b 100644
--- a/pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart
+++ b/pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart
@@ -34,6 +34,12 @@ class InvokeDynamicSpecializer {
     return null;
   }
 
+  void clearAllSideEffects(HInstruction instruction) {
+    instruction.sideEffects.clearAllSideEffects();
+    instruction.sideEffects.clearAllDependencies();
+    instruction.setUseGvn();
+  }
+
   Operation operation(ConstantSystem constantSystem) => null;
 
   static InvokeDynamicSpecializer lookupSpecializer(Selector selector) {
@@ -85,6 +91,11 @@ class InvokeDynamicSpecializer {
           return const CodeUnitAtSpecializer();
         }
       }
+      if (selector.argumentCount == 0 && selector.namedArguments.length == 0) {
+        if (selector.name == 'round') {
+          return const RoundSpecializer();
+        }
+      }
     }
     return const InvokeDynamicSpecializer();
   }
@@ -219,12 +230,6 @@ abstract class BinaryArithmeticSpecializer extends InvokeDynamicSpecializer {
     return null;
   }
 
-  void clearAllSideEffects(HInstruction instruction) {
-    instruction.sideEffects.clearAllSideEffects();
-    instruction.sideEffects.clearAllDependencies();
-    instruction.setUseGvn();
-  }
-
   bool inputsArePositiveIntegers(HInstruction instruction, Compiler compiler) {
     HInstruction left = instruction.inputs[1];
     HInstruction right = instruction.inputs[2];
@@ -759,3 +764,22 @@ class CodeUnitAtSpecializer extends InvokeDynamicSpecializer {
     return null;
   }
 }
+
+class RoundSpecializer extends InvokeDynamicSpecializer {
+  const RoundSpecializer();
+
+  UnaryOperation operation(ConstantSystem constantSystem) {
+    return constantSystem.round;
+  }
+
+  HInstruction tryConvertToBuiltin(
+      HInvokeDynamic instruction, Compiler compiler) {
+    HInstruction receiver = instruction.getDartReceiver(compiler);
+    if (receiver.isNumberOrNull(compiler)) {
+      // Even if there is no builtin equivalent instruction, we know the
+      // instruction does not have any side effect, and that it can be GVN'ed.
+      clearAllSideEffects(instruction);
+    }
+    return null;
+  }
+}