Fix bug in SsaConstructionFieldTypes: handle mulitple assignments to the same field.

sdk/lib/_internal/compiler/implementation/ssa/optimize.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/optimize.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/optimize.dart	(revision 23664)
+++ sdk/lib/_internal/compiler/implementation/ssa/optimize.dart	(working copy)
@@ -1465,13 +1465,25 @@
     HInstruction value = node.value;
     HType type = value.instructionType;
     // [HFieldSet] is also used for variables in try/catch.
-    if (field.isField()) allSetters.add(field);
+    if (!field.isField()) return;
+    allSetters.add(field);
     // Don't handle fields defined in superclasses. Given that the field is
     // always added to the [allSetters] set, setting a field defined in a
     // superclass will get an inferred type of UNKNOWN.
-    if (identical(work.element.getEnclosingClass(), field.getEnclosingClass()) &&
-        !value.instructionType.isUnknown()) {
-      currentFieldSetters[field] = type;
+    if (work.element.getEnclosingClass() == field.getEnclosingClass()) {
+      HType existing = currentFieldSetters[field];
+      // If we have seen an assignment already, we check if
+      // it's of the same type. If it's not, we remove the current
+      // field type information.
+      if (existing != null) {
+        if (existing == type) {
+          return;
+        } else {
+          currentFieldSetters.remove(field);

[kasperl, 2013/06/06 08:15:12]

Can we then get another field type added after this? Should we add a marker
instead of removing it? Need a test with three field sets?

[ngeoffray, 2013/06/06 08:44:00]

Good catch. Done.

+        }
+      } else if (!type.isUnknown()) {
+        currentFieldSetters[field] = type;
+      }
     }
   }