Start work on a non-complete type inferrer. Currently only analyzes return types.

sdk/lib/_internal/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.
 
 part of ssa;
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
@@ skipping 1351 matching lines @@
         && element == other.element;
   }
 
   HType computeDesiredTypeForInput(HInstruction input,
                                    HTypeMap types,
                                    Compiler compiler) {
     return specializer.computeDesiredTypeForInput(this, input, types, compiler);
   }
 
   HType computeTypeFromInputTypes(HTypeMap types, Compiler compiler) {
-    return specializer.computeTypeFromInputTypes(this, types, compiler);
+    HType type = specializer.computeTypeFromInputTypes(this, types, compiler);
+    return type.isUnknown() ? guaranteedType : type;
   }
 }
 
 class HInvokeClosure extends HInvokeDynamic {
   HInvokeClosure(Selector selector, List<HInstruction> inputs)
     : super(selector, null, inputs) {
     assert(selector.isClosureCall());
   }
   accept(HVisitor visitor) => visitor.visitInvokeClosure(this);
 }
@@ skipping 281 matching lines @@
   accept(HVisitor visitor) => visitor.visitSwitch(this);
 
   String toString() => "HSwitch cases = $inputs";
 }
 
 // TODO(floitsch): Should HBinaryArithmetic really be the super class of
 // HBinaryBitOp?
 abstract class HBinaryBitOp extends HBinaryArithmetic {
   HBinaryBitOp(HInstruction left, HInstruction right) : super(left, right);
   HType get guaranteedType => HType.INTEGER;
+  HType computeTypeFromInputTypes(HTypeMap types, Compiler compiler) {
+    return guaranteedType;
+  }
 }
 
 class HShiftLeft extends HBinaryBitOp {
   HShiftLeft(HInstruction left, HInstruction right) : super(left, right);
   accept(HVisitor visitor) => visitor.visitShiftLeft(this);
 
   BinaryOperation operation(ConstantSystem constantSystem)
       => constantSystem.shiftLeft;
   int typeCode() => HInstruction.SHIFT_LEFT_TYPECODE;
   bool typeEquals(other) => other is HShiftLeft;
@@ skipping 1017 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);
 }