Support fast-path allocation for subclass constructors with correctly initialized initial maps.

src/arm/builtins-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_ARM
 
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 370 matching lines @@
     // the preconditions is not met, the code bails out to the runtime call.
     Label rt_call, allocated;
     if (FLAG_inline_new) {
       ExternalReference debug_step_in_fp =
           ExternalReference::debug_step_in_fp_address(isolate);
       __ mov(r2, Operand(debug_step_in_fp));
       __ ldr(r2, MemOperand(r2));
       __ tst(r2, r2);
       __ b(ne, &rt_call);
 
-      // Fall back to runtime if the original constructor and function differ.
-      __ cmp(r1, r3);
+      // Verify that the original constructor is a JSFunction.
+      __ CompareObjectType(r3, r5, r4, JS_FUNCTION_TYPE);
       __ b(ne, &rt_call);
 
       // Load the initial map and verify that it is in fact a map.
-      // r1: constructor function
-      __ ldr(r2, FieldMemOperand(r1, JSFunction::kPrototypeOrInitialMapOffset));
+      // r3: original constructor
+      __ ldr(r2, FieldMemOperand(r3, JSFunction::kPrototypeOrInitialMapOffset));
       __ JumpIfSmi(r2, &rt_call);
       __ CompareObjectType(r2, r5, r4, MAP_TYPE);
       __ b(ne, &rt_call);
 
+      // Fall back to runtime if the expected base constructor and base
+      // constructor differ.
+      __ ldr(r5, FieldMemOperand(r2, Map::kConstructorOrBackPointerOffset));
+      __ cmp(r1, r5);
+      __ b(ne, &rt_call);
+
       // Check that the constructor is not constructing a JSFunction (see
       // comments in Runtime_NewObject in runtime.cc). In which case the
       // initial map's instance type would be JS_FUNCTION_TYPE.
       // r1: constructor function
       // r2: initial map
       __ CompareInstanceType(r2, r5, JS_FUNCTION_TYPE);
       __ b(eq, &rt_call);
 
       if (!is_api_function) {
         Label allocate;
         MemOperand bit_field3 = FieldMemOperand(r2, Map::kBitField3Offset);
         // Check if slack tracking is enabled.
         __ ldr(r4, bit_field3);
         __ DecodeField<Map::Counter>(r3, r4);
         __ cmp(r3, Operand(Map::kSlackTrackingCounterEnd));
         __ b(lt, &allocate);
         // Decrease generous allocation count.
         __ sub(r4, r4, Operand(1 << Map::Counter::kShift));
         __ str(r4, bit_field3);
         __ cmp(r3, Operand(Map::kSlackTrackingCounterEnd));
         __ b(ne, &allocate);
 
-        __ push(r1);
+        __ Push(r1, r2);
 
-        __ Push(r2, r1);  // r1 = constructor
+        __ push(r2);  // r2 = intial map
         __ CallRuntime(Runtime::kFinalizeInstanceSize, 1);
 
         __ pop(r2);
         __ pop(r1);
 
         __ bind(&allocate);
       }
 
       // Now allocate the JSObject on the heap.
       // r1: constructor function
@@ skipping 1499 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM