Allow for optimized code map to have zero entries.

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 587496fecd1ddf53a32a2a5564aa9cb43f086074..2168d1c3b105cebeb4385133eebae29b99f548c7 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -1965,71 +1965,59 @@ void CodeStubGraphBuilderBase::BuildInstallFromOptimizedCodeMap(
   is_optimized.Else();
   {
     AddIncrementCounter(counters->fast_new_closure_try_optimized());
-    // optimized_map points to fixed array of 3-element entries
-    // (native context, optimized code, literals).
-    // Map must never be empty, so check the first elements.
+    // The {optimized_map} points to fixed array of 4-element entries:
+    //   (native context, optimized code, literals, ast-id).
+    // Iterate through the {optimized_map} backwards. After the loop, if no
+    // matching optimized code was found, install unoptimized code.
+    //   for(i = map.length() - SharedFunctionInfo::kEntryLength;
+    //       i >= SharedFunctionInfo::kEntriesStart;
+    //       i -= SharedFunctionInfo::kEntryLength) { ... }
     HValue* first_entry_index =
         Add<HConstant>(SharedFunctionInfo::kEntriesStart);
-    IfBuilder already_in(this);
-    BuildCheckAndInstallOptimizedCode(js_function, native_context, &already_in,
-                                      optimized_map, first_entry_index);
-    already_in.Else();
+    HValue* shared_function_entry_length =
+        Add<HConstant>(SharedFunctionInfo::kEntryLength);
+    LoopBuilder loop_builder(this, context(), LoopBuilder::kPostDecrement,
+                             shared_function_entry_length);
+    HValue* array_length = Add<HLoadNamedField>(
+        optimized_map, nullptr, HObjectAccess::ForFixedArrayLength());
+    HValue* start_pos =
+        AddUncasted<HSub>(array_length, shared_function_entry_length);
+    HValue* slot_iterator =
+        loop_builder.BeginBody(start_pos, first_entry_index, Token::GTE);
     {
-      // Iterate through the rest of map backwards. Do not double check first
-      // entry. After the loop, if no matching optimized code was found,
-      // install unoptimized code.
-      // for(i = map.length() - SharedFunctionInfo::kEntryLength;
-      //     i > SharedFunctionInfo::kEntriesStart;
-      //     i -= SharedFunctionInfo::kEntryLength) { .. }
-      HValue* shared_function_entry_length =
-          Add<HConstant>(SharedFunctionInfo::kEntryLength);
-      LoopBuilder loop_builder(this,
-                               context(),
-                               LoopBuilder::kPostDecrement,
-                               shared_function_entry_length);
-      HValue* array_length = Add<HLoadNamedField>(
-          optimized_map, nullptr, HObjectAccess::ForFixedArrayLength());
-      HValue* start_pos = AddUncasted<HSub>(array_length,
-                                            shared_function_entry_length);
-      HValue* slot_iterator = loop_builder.BeginBody(start_pos,
-                                                     first_entry_index,
-                                                     Token::GT);
+      IfBuilder done_check(this);
+      BuildCheckAndInstallOptimizedCode(js_function, native_context,
+                                        &done_check, optimized_map,
+                                        slot_iterator);
+      // Fall out of the loop
+      loop_builder.Break();
+    }
+    loop_builder.EndBody();
+
+    // If {slot_iterator} is less than the first entry index, then we failed to
+    // find a context-dependent code and try context-independent code next.
+    IfBuilder no_optimized_code_check(this);
+    no_optimized_code_check.If<HCompareNumericAndBranch>(
+        slot_iterator, first_entry_index, Token::LT);
+    no_optimized_code_check.Then();
+    {
+      IfBuilder shared_code_check(this);
+      HValue* shared_code =
+          Add<HLoadNamedField>(optimized_map, nullptr,
+                               HObjectAccess::ForOptimizedCodeMapSharedCode());
+      shared_code_check.IfNot<HCompareObjectEqAndBranch>(
+          shared_code, graph()->GetConstantUndefined());
+      shared_code_check.Then();
       {
-        IfBuilder done_check(this);
-        BuildCheckAndInstallOptimizedCode(js_function, native_context,
-                                          &done_check,
-                                          optimized_map,
-                                          slot_iterator);
-        // Fall out of the loop
-        loop_builder.Break();
+        // Store the context-independent optimized code.
+        HValue* literals = Add<HConstant>(factory->empty_fixed_array());
+        BuildInstallOptimizedCode(js_function, native_context, shared_code,
+                                  literals);
       }
-      loop_builder.EndBody();
-
-      // If slot_iterator equals first entry index, then we failed to find a
-      // context-dependent code and try context-independent code next.
-      IfBuilder no_optimized_code_check(this);
-      no_optimized_code_check.If<HCompareNumericAndBranch>(
-          slot_iterator, first_entry_index, Token::EQ);
-      no_optimized_code_check.Then();
+      shared_code_check.Else();
       {
-        IfBuilder shared_code_check(this);
-        HValue* shared_code = Add<HLoadNamedField>(
-            optimized_map, nullptr,
-            HObjectAccess::ForOptimizedCodeMapSharedCode());
-        shared_code_check.IfNot<HCompareObjectEqAndBranch>(
-            shared_code, graph()->GetConstantUndefined());
-        shared_code_check.Then();
-        {
-          // Store the context-independent optimized code.
-          HValue* literals = Add<HConstant>(factory->empty_fixed_array());
-          BuildInstallOptimizedCode(js_function, native_context, shared_code,
-                                    literals);
-        }
-        shared_code_check.Else();
-        {
-          // Store the unoptimized code.
-          BuildInstallCode(js_function, shared_info);
-        }
+        // Store the unoptimized code.
+        BuildInstallCode(js_function, shared_info);
       }
     }
   }