track global accesses to constant types

src/code-stubs-hydrogen.cc

Index: src/code-stubs-hydrogen.cc
diff --git a/src/code-stubs-hydrogen.cc b/src/code-stubs-hydrogen.cc
index 3ca301ca6c3a6c215097d6f0afbfa575e5df08e7..1614af351331e4d5cff9bcbb6accee835437e4eb 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -1324,10 +1324,10 @@ HValue* CodeStubGraphBuilder<StoreGlobalStub>::BuildCodeInitializedStub() {
         Add<HLoadNamedField>(proxy, nullptr, HObjectAccess::ForMap());
     HValue* global =
         Add<HLoadNamedField>(proxy_map, nullptr, HObjectAccess::ForPrototype());
-    Handle<Map> placeholder_map = isolate()->factory()->meta_map();
-    HValue* cell = Add<HConstant>(Map::WeakCellForMap(placeholder_map));
-    HValue* expected_map =
-        Add<HLoadNamedField>(cell, nullptr, HObjectAccess::ForWeakCellValue());
+    HValue* map_cell = Add<HConstant>(isolate()->factory()->NewWeakCell(
+        StoreGlobalStub::global_map_placeholder(isolate())));
+    HValue* expected_map = Add<HLoadNamedField>(
+        map_cell, nullptr, HObjectAccess::ForWeakCellValue());
     HValue* map =
         Add<HLoadNamedField>(global, nullptr, HObjectAccess::ForMap());
     IfBuilder map_check(this);
@@ -1342,9 +1342,15 @@ HValue* CodeStubGraphBuilder<StoreGlobalStub>::BuildCodeInitializedStub() {
                                       HObjectAccess::ForWeakCellValue());
   Add<HCheckHeapObject>(cell);
   HObjectAccess access = HObjectAccess::ForPropertyCellValue();
+  // Load the payload of the global parameter cell. A hole indicates that the
+  // cell has been invalidated and that the store must be handled by the
+  // runtime.
   HValue* cell_contents = Add<HLoadNamedField>(cell, nullptr, access);
 
-  if (stub->is_constant()) {
+  auto cell_type = stub->cell_type();
+  if (cell_type == PropertyCellType::kConstant ||
+      cell_type == PropertyCellType::kUndefined) {
+    // This is always valid for all states a cell can be in.
     IfBuilder builder(this);
     builder.If<HCompareObjectEqAndBranch>(cell_contents, value);
     builder.Then();
@@ -1352,16 +1358,44 @@ HValue* CodeStubGraphBuilder<StoreGlobalStub>::BuildCodeInitializedStub() {
         Deoptimizer::kUnexpectedCellContentsInConstantGlobalStore);
     builder.End();
   } else {
-    // Load the payload of the global parameter cell. A hole indicates that the
-    // property has been deleted and that the store must be handled by the
-    // runtime.
     IfBuilder builder(this);
     HValue* hole_value = graph()->GetConstantHole();
     builder.If<HCompareObjectEqAndBranch>(cell_contents, hole_value);
     builder.Then();
     builder.Deopt(Deoptimizer::kUnexpectedCellContentsInGlobalStore);
     builder.Else();
-    Add<HStoreNamedField>(cell, access, value);
+    // When dealing with constant types, the type may be allowed to change, as
+    // long as optimized code remains valid.
+    StoreFieldOrKeyedMode store_mode = INITIALIZING_STORE;
+    if (cell_type == PropertyCellType::kConstantType) {
+      // store_mode = STORE_TO_INITIALIZED_ENTRY;

[dcarney, 2015/04/21 07:20:07]

i had to comment these out because there was some issues with smi not doing what
i expected them to do. is there something else i need to do?

+      switch (stub->constant_type()) {
+        case PropertyCellConstantType::kSmi:
+          Add<HCheckSmi>(value);

[Toon Verwaest, 2015/04/21 08:06:23]

This shouldn't be necessary; there'll be (should be) a t->s change due to
access.WithRepresentation(Smi) which will check.

+          access = access.WithRepresentation(Representation::Smi());

[dcarney, 2015/04/21 07:20:07]

here i have a smi check and a withrepresentation. do we want to convert doubles
into smis in this code path or just deopt?

+          break;
+        case PropertyCellConstantType::kStableMap: {
+          // It is sufficient here to check that the value and cell contents
+          // have identical maps, no matter if they are stable or not or if they
+          // are the maps that were originally in the cell or not. If optimized
+          // code will deopt when a cell has a unstable map and if it has a
+          // dependency on a stable map, it will deopt if the map destabilizes.
+          Add<HCheckHeapObject>(value);

[Toon Verwaest, 2015/04/21 08:06:23]

This OTOH is necessary since there's no such thing as t->heapobject.

+          Add<HCheckHeapObject>(cell_contents);
+          HValue* expected_map = Add<HLoadNamedField>(cell_contents, nullptr,
+                                                      HObjectAccess::ForMap());
+          HValue* map =
+              Add<HLoadNamedField>(value, nullptr, HObjectAccess::ForMap());
+          IfBuilder map_check(this);
+          map_check.IfNot<HCompareObjectEqAndBranch>(expected_map, map);
+          map_check.ThenDeopt(Deoptimizer::kUnknownMap);
+          map_check.End();
+          access = access.WithRepresentation(Representation::HeapObject());
+          break;
+        }
+      }
+    }
+    Add<HStoreNamedField>(cell, access, value, store_mode);
     builder.End();
   }