dart2js cps: Add a pass for eliminating bounds checks.

pkg/compiler/lib/src/cps_ir/type_mask_system.dart

Index: pkg/compiler/lib/src/cps_ir/type_mask_system.dart
diff --git a/pkg/compiler/lib/src/cps_ir/type_mask_system.dart b/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
index e05db65625bc306a7a9b19114d4b0f488b4fa077..ab6b0944362e281a880ccfdbb01304f08b82bf55 100644
--- a/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
@@ -32,6 +32,7 @@ class TypeMaskSystem {
   TypeMask get functionType => inferrer.functionType;
   TypeMask get boolType => inferrer.boolType;
   TypeMask get intType => inferrer.intType;
+  TypeMask get uint32Type => inferrer.uint32Type;
   TypeMask get doubleType => inferrer.doubleType;
   TypeMask get numType => inferrer.numType;
   TypeMask get stringType => inferrer.stringType;
@@ -42,6 +43,7 @@ class TypeMaskSystem {
   TypeMask get extendableNativeListType => backend.extendableArrayType;
 
   TypeMask numStringBoolType;
+  TypeMask fixedLengthType;
 
   ClassElement get jsNullClass => backend.jsNullClass;
 
@@ -63,6 +65,10 @@ class TypeMaskSystem {
     numStringBoolType =
         new TypeMask.unionOf(<TypeMask>[anyNum, anyString, anyBool],
             classWorld);
+
+    fixedLengthType =
+        new TypeMask.unionOf(<TypeMask>[stringType, inferrer.fixedListType],

[sra1, 2015/09/30 21:54:20]

This needs to include the typed arrays.

[asgerf, 2015/10/01 09:49:34]

Done.

Also, there was a pretty serious bug here since 'fixedListType' actually
resolves to the core List class:

TypesTask.fixedListType -> 
JavaScriptBackend.fixedListImplementation -> 
Compiler.listClass -> 
CoreTypes.listClass

This seems like an issue with one of the above classes, since a bunch of List
variants actually return the same type mask.

[asgerf, 2015/10/01 10:35:25]

Oh nevermind, I was confused by IntelliJ. JavaScriptBackend's
fixedListImplementation actually returns the right class.

+            classWorld);
   }
 
   bool methodUsesReceiverArgument(FunctionElement function) {
@@ -183,6 +189,11 @@ class TypeMaskSystem {
     return areDisjoint(t, doubleType);
   }
 
+  bool isDefinitelyUInt32(TypeMask t, {bool allowNull: false}) {
+    if (!allowNull && t.isNullable) return false;
+    return t.satisfies(backend.jsUInt32Class, classWorld);
+  }
+
   bool isDefinitelyInt(TypeMask t, {bool allowNull: false}) {
     if (!allowNull && t.isNullable) return false;
     return t.satisfies(backend.jsIntClass, classWorld);
@@ -214,6 +225,16 @@ class TypeMaskSystem {
     return t.nonNullable().satisfies(backend.jsIndexableClass, classWorld);
   }
 
+  bool isDefinitelyMutableIndexable(TypeMask t, {bool allowNull: false}) {
+    if (!allowNull && t.isNullable) return false;
+    return t.nonNullable().satisfies(backend.jsMutableIndexableClass, classWorld);
+  }
+
+  bool isDefinitelyFixedLengthIndexable(TypeMask t, {bool allowNull: false}) {
+    if (!allowNull && t.isNullable) return false;
+    return fixedLengthType.containsMask(t.nonNullable(), classWorld);
+  }
+
   bool areDisjoint(TypeMask leftType, TypeMask rightType) {
     TypeMask intersection = leftType.intersection(rightType, classWorld);
     return intersection.isEmpty && !intersection.isNullable;