Optimize out checkInt, checkNum and checkString

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

Index: pkg/compiler/lib/src/ssa/optimize.dart
diff --git a/pkg/compiler/lib/src/ssa/optimize.dart b/pkg/compiler/lib/src/ssa/optimize.dart
index 6ff4e783c2628f33e7a24e2fe26721b75945ba10..e8c546a42b03ff4ec80de283618a7b05b856c8df 100644
--- a/pkg/compiler/lib/src/ssa/optimize.dart
+++ b/pkg/compiler/lib/src/ssa/optimize.dart
@@ -952,7 +952,9 @@ class SsaInstructionSimplifier extends HBaseVisitor
 
   HInstruction visitInvokeStatic(HInvokeStatic node) {
     propagateConstantValueToUses(node);
-    if (node.element == backend.helpers.checkConcurrentModificationError) {
+    Element element = node.element;
+
+    if (element == backend.helpers.checkConcurrentModificationError) {
       if (node.inputs.length == 2) {
         HInstruction firstArgument = node.inputs[0];
         if (firstArgument is HConstant) {
@@ -960,6 +962,21 @@ class SsaInstructionSimplifier extends HBaseVisitor
           if (constant.constant.isTrue) return constant;
         }
       }
+    } else if (element == backend.helpers.checkInt) {
+      if (node.inputs.length == 1) {
+        HInstruction argument = node.inputs[0];
+        if (argument.isInteger(compiler)) return argument;
+      }
+    } else if (element == backend.helpers.checkNum) {
+      if (node.inputs.length == 1) {
+        HInstruction argument = node.inputs[0];
+        if (argument.isNumber(compiler)) return argument;
+      }
+    } else if (element == backend.helpers.checkString) {
+      if (node.inputs.length == 1) {
+        HInstruction argument = node.inputs[0];
+        if (argument.isString(compiler)) return argument;
+      }
     }
     return node;
   }