Use GVN for length loads from arrays and strings.

lib/compiler/implementation/ssa/nodes.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.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
@@ skipping 974 matching lines @@
  * A [HCheck] instruction is an instruction that might do a dynamic
  * check at runtime on another instruction. To have proper instruction
  * dependencies in the graph, instructions that depend on the check
  * being done reference the [HCheck] instruction instead of the
  * instruction itself.
  */
 abstract class HCheck extends HInstruction {
   HCheck(inputs) : super(inputs);
   HInstruction get checkedInput() => inputs[0];
   bool isStatement() => true;
+  void prepareGvn() {
+    assert(!hasSideEffects());
+    setUseGvn();
+  }
 }
 
 class HTypeGuard extends HCheck {
   final int state;
   final HType guardedType;
   bool isOn = false;
   int checkedInputIndex = 0;
 
   HTypeGuard(this.guardedType, this.state, List<HInstruction> env) : super(env);
 
-  void prepareGvn() {
-    assert(!hasSideEffects());
-    setUseGvn();
-  }
-
   HInstruction get guarded() => inputs[checkedInputIndex];
   HInstruction get checkedInput() => guarded;
 
   HType computeTypeFromInputTypes() {
     return isOn ? guardedType : guarded.propagatedType;
   }
 
   HType get guaranteedType() => isOn ? guardedType : HType.UNKNOWN;
 
   bool isControlFlow() => true;
@@ skipping 16 matching lines @@
    * Default is that all checks must be performed dynamically.
    */
   int staticChecks = FULL_CHECK;
 
   HBoundsCheck(length, index) : super(<HInstruction>[length, index]);
 
   HInstruction get length() => inputs[1];
   HInstruction get index() => inputs[0];
   bool isControlFlow() => true;
 
-  void prepareGvn() {
-    assert(!hasSideEffects());
-    setUseGvn();
-  }
-
   HType get guaranteedType() => HType.INTEGER;
 
   accept(HVisitor visitor) => visitor.visitBoundsCheck(this);
   int typeCode() => 2;
   bool typeEquals(other) => other is HBoundsCheck;
   bool dataEquals(HInstruction other) => true;
 }
 
 class HIntegerCheck extends HCheck {
   bool alwaysFalse = false;
 
   HIntegerCheck(value) : super(<HInstruction>[value]);
 
   HInstruction get value() => inputs[0];
   bool isControlFlow() => true;
 
-  void prepareGvn() {
-    assert(!hasSideEffects());
-    setUseGvn();
-  }
-
   HType get guaranteedType() => HType.INTEGER;
 
   accept(HVisitor visitor) => visitor.visitIntegerCheck(this);
   int typeCode() => 3;
   bool typeEquals(other) => other is HIntegerCheck;
   bool dataEquals(HInstruction other) => true;
 }
 
 class HConditionalBranch extends HControlFlow {
   HConditionalBranch(inputs) : super(inputs);
@@ skipping 153 matching lines @@
       if (name == const SourceString('add')
           || name == const SourceString('removeLast')) {
         return HType.MUTABLE_ARRAY;
       }
     }
     return HType.UNKNOWN;
   }
 
   void prepareGvn() {
     if (isLengthGetterOnStringOrArray()) {
-      clearAllSideEffects();
+      setUseGvn();
+      setDependsOnSomething();
     } else {
       setAllSideEffects();
     }
   }
 
   int typeCode() => 4;
   bool typeEquals(other) => other is HInvokeInterceptor;
   bool dataEquals(HInvokeInterceptor other) {
     return getter == other.getter && name == other.name;
   }
@@ skipping 1028 matching lines @@
   }
 
   bool isChecked() => kind != NO_CHECK;
   bool isCheckedModeCheck() => kind == CHECKED_MODE_CHECK;
   bool isArgumentTypeCheck() => kind == ARGUMENT_TYPE_CHECK;
 
   HType get guaranteedType() => type;
 
   accept(HVisitor visitor) => visitor.visitTypeConversion(this);
 
-  bool hasSideEffects() => kind != NO_CHECK;
   bool isStatement() => kind == ARGUMENT_TYPE_CHECK;
   bool isControlFlow() => kind == ARGUMENT_TYPE_CHECK;
 }
 
 class HStringConcat extends HInstruction {
   final Node node;
   HStringConcat(HInstruction left, HInstruction right, this.node)
       : super(<HInstruction>[left, right]);
   HType get guaranteedType() => HType.STRING;
 
@@ skipping 325 matching lines @@
   HBasicBlock get start() => expression.start;
   HBasicBlock get end() {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty());
     return statements.last().end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }