Fix misoptimization of 'is' test

runtime/vm/optimizer.cc

+// Copyright (c) 2017, 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.
+
+#include "vm/optimizer.h"
+
+#include "vm/intermediate_language.h"
+#include "vm/object.h"
+
+namespace dart {
+
+static bool CidTestResultsContains(const ZoneGrowableArray<intptr_t>& results,
+                                   intptr_t test_cid) {
+  for (intptr_t i = 0; i < results.length(); i += 2) {
+    if (results[i] == test_cid) return true;
+  }
+  return false;
+}
+
+
+static void TryAddTest(ZoneGrowableArray<intptr_t>* results,
+                       intptr_t test_cid,
+                       bool result) {
+  if (!CidTestResultsContains(*results, test_cid)) {
+    results->Add(test_cid);
+    results->Add(result);
+  }
+}
+
+
+// Used when we only need the positive result because we return false by
+// default.
+static void PurgeNegativeTestCidsEntries(ZoneGrowableArray<intptr_t>* results) {
+  // We can't purge the Smi entry at the beginning since it is used in the
+  // Smi check before the Cid is loaded.
+  int dest = 2;
+  for (intptr_t i = 2; i < results->length(); i += 2) {
+    if (results->At(i + 1) != 0) {
+      (*results)[dest++] = results->At(i);
+      (*results)[dest++] = results->At(i + 1);
+    }
+  }
+  results->SetLength(dest);
+}
+
+
+bool Optimizer::SpecializeTestCidsForNumericTypes(
+    ZoneGrowableArray<intptr_t>* results,
+    const AbstractType& type) {
+  ASSERT(results->length() >= 2);  // At least on entry.
+  const ClassTable& class_table = *Isolate::Current()->class_table();
+  if ((*results)[0] != kSmiCid) {
+    const Class& cls = Class::Handle(class_table.At(kSmiCid));
+    const Class& type_class = Class::Handle(type.type_class());
+    const bool smi_is_subtype =
+        cls.IsSubtypeOf(Object::null_type_arguments(), type_class,
+                        Object::null_type_arguments(), NULL, NULL, Heap::kOld);
+    results->Add((*results)[results->length() - 2]);
+    results->Add((*results)[results->length() - 2]);
+    for (intptr_t i = results->length() - 3; i > 1; --i) {
+      (*results)[i] = (*results)[i - 2];
+    }
+    (*results)[0] = kSmiCid;
+    (*results)[1] = smi_is_subtype;
+  }
+
+  ASSERT(type.IsInstantiated() && !type.IsMalformedOrMalbounded());
+  ASSERT(results->length() >= 2);
+  if (type.IsSmiType()) {
+    ASSERT((*results)[0] == kSmiCid);
+    PurgeNegativeTestCidsEntries(results);
+    return false;
+  } else if (type.IsIntType()) {
+    ASSERT((*results)[0] == kSmiCid);
+    TryAddTest(results, kMintCid, true);
+    TryAddTest(results, kBigintCid, true);
+    // Cannot deoptimize since all tests returning true have been added.
+    PurgeNegativeTestCidsEntries(results);
+    return false;
+  } else if (type.IsNumberType()) {
+    ASSERT((*results)[0] == kSmiCid);
+    TryAddTest(results, kMintCid, true);
+    TryAddTest(results, kBigintCid, true);
+    TryAddTest(results, kDoubleCid, true);
+    PurgeNegativeTestCidsEntries(results);
+    return false;
+  } else if (type.IsDoubleType()) {
+    ASSERT((*results)[0] == kSmiCid);
+    TryAddTest(results, kDoubleCid, true);
+    PurgeNegativeTestCidsEntries(results);
+    return false;
+  }
+  return true;  // May deoptimize since we have not identified all 'true' tests.
+}
+
+}  // namespace dart