Recognize simple numeric computations for field type recording.

lib/compiler/implementation/ssa/codegen.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.
 
 class SsaCodeGeneratorTask extends CompilerTask {
   final JavaScriptBackend backend;
   SsaCodeGeneratorTask(JavaScriptBackend backend)
       : this.backend = backend,
         super(backend.compiler);
   String get name() => 'SSA code generator';
@@ skipping 1815 matching lines @@
     use(node.receiver, JSPrecedence.MEMBER_PRECEDENCE);
     buffer.add('.');
     buffer.add(name);
     beginExpression(JSPrecedence.MEMBER_PRECEDENCE);
     Type type = node.receiver.propagatedType.computeType(compiler);
     if (type != null) {
       world.registerFieldGetter(node.element.name, type);
     }
   }
 
+  // Determine if an instruction is a simple number computation
+  // involving only things with guaranteed number types and a given
+  // field.
+  bool isSimpleFieldNumberComputation(HInstruction value, HFieldSet node) {
+    if (value.guaranteedType.union(HType.NUMBER) == HType.NUMBER) return true;
+    if (value is HBinaryArithmetic) {
+      return (isSimpleFieldNumberComputation(value.left, node) &&
+              isSimpleFieldNumberComputation(value.right, node));
+    }
+    if (value is HFieldGet) return value.element == node.element;
+    return false;
+  }
+
   visitFieldSet(HFieldSet node) {
     if (work.element.isGenerativeConstructorBody() &&
         node.element.enclosingElement.isClass() &&
         node.value.hasGuaranteedType() &&
         node.block.dominates(currentGraph.exit)) {
       backend.updateFieldConstructorSetters(node.element,
                                             node.value.guaranteedType);
     }
     String name = compiler.namer.getName(node.element);
     beginExpression(JSPrecedence.ASSIGNMENT_PRECEDENCE);
     use(node.receiver, JSPrecedence.MEMBER_PRECEDENCE);
     buffer.add('.');
     buffer.add(name);
     Type type = node.receiver.propagatedType.computeType(compiler);
     if (type != null) {
       if (!work.element.isGenerativeConstructorBody()) {
         world.registerFieldSetter(node.element.name, type);
       }
-      backend.updateFieldSetters(node.element,
-                                 node.value.propagatedType);
+      // Determine the types seen so far for the field. If only number
+      // types have been seen and the value of the field set is a
+      // simple number computation only depending on that field, we
+      // can safely keep the number type for the field.
+      HType fieldSettersType = backend.fieldSettersTypeSoFar(node.element);
+      HType initializersType = backend.typeFromInitializersSoFar(node.element);
+      HType fieldType = fieldSettersType.union(initializersType);
+      if (HType.NUMBER.union(fieldType) == HType.NUMBER &&
+          isSimpleFieldNumberComputation(node.value, node)) {
+        backend.updateFieldSetters(node.element, HType.NUMBER);
+      } else {
+        backend.updateFieldSetters(node.element,
+                                   node.value.propagatedType);
+      }
     }
     buffer.add(' = ');
     use(node.value, JSPrecedence.ASSIGNMENT_PRECEDENCE);
     endExpression(JSPrecedence.ASSIGNMENT_PRECEDENCE);
   }
 
   visitLocalGet(HLocalGet node) {
     use(node.receiver, JSPrecedence.EXPRESSION_PRECEDENCE);
   }
 
@@ skipping 1245 matching lines @@
   if (leftType.canBeNull() && rightType.canBeNull()) {
     if (left.isConstantNull() || right.isConstantNull() ||
         (leftType.isPrimitive() && leftType == rightType)) {
       return '==';
     }
     return null;
   } else {
     return '===';
   }
 }