Further robustify the keyed lookup cache against unlucky hash

src/ia32/ic-ia32.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 520 matching lines @@
   __ mov(ebx, FieldOperand(edx, HeapObject::kMapOffset));
   __ mov(ecx, ebx);
   __ shr(ecx, KeyedLookupCache::kMapHashShift);
   __ mov(edi, FieldOperand(eax, String::kHashFieldOffset));
   __ shr(edi, String::kHashShift);
   __ xor_(ecx, edi);
   __ and_(ecx, KeyedLookupCache::kCapacityMask & KeyedLookupCache::kHashMask);
 
   // Load the key (consisting of map and symbol) from the cache and
   // check for match.
-  Label try_second_entry, hit_on_first_entry, load_in_object_property;
+  Label load_in_object_property;
+  static const int kEntriesPerBucket = KeyedLookupCache::kEntriesPerBucket;
+  Label hit_on_nth_entry[kEntriesPerBucket];
   ExternalReference cache_keys =
       ExternalReference::keyed_lookup_cache_keys(masm->isolate());
-  __ mov(edi, ecx);
-  __ shl(edi, kPointerSizeLog2 + 1);
-  __ cmp(ebx, Operand::StaticArray(edi, times_1, cache_keys));
-  __ j(not_equal, &try_second_entry);
-  __ add(edi, Immediate(kPointerSize));
-  __ cmp(eax, Operand::StaticArray(edi, times_1, cache_keys));
-  __ j(equal, &hit_on_first_entry);
 
-  __ bind(&try_second_entry);
+  for (int i = 0; i < kEntriesPerBucket - 1; i++) {
+    Label try_next_entry;
+    __ mov(edi, ecx);
+    __ shl(edi, kPointerSizeLog2 + 1);
+    if (i != 0) {
+      __ add(edi, Immediate(kPointerSize * i * 2));
+    }
+    __ cmp(ebx, Operand::StaticArray(edi, times_1, cache_keys));
+    __ j(not_equal, &try_next_entry);
+    __ add(edi, Immediate(kPointerSize));
+    __ cmp(eax, Operand::StaticArray(edi, times_1, cache_keys));
+    __ j(equal, &hit_on_nth_entry[i]);
+    __ bind(&try_next_entry);
+  }
+
   __ lea(edi, Operand(ecx, 1));
   __ shl(edi, kPointerSizeLog2 + 1);
+  __ add(edi, Immediate(kPointerSize * (kEntriesPerBucket - 1) * 2));
   __ cmp(ebx, Operand::StaticArray(edi, times_1, cache_keys));
   __ j(not_equal, &slow);
   __ add(edi, Immediate(kPointerSize));
   __ cmp(eax, Operand::StaticArray(edi, times_1, cache_keys));
   __ j(not_equal, &slow);
 
   // Get field offset.
   // edx     : receiver
   // ebx     : receiver's map
   // eax     : key
   // ecx     : lookup cache index
   ExternalReference cache_field_offsets =
       ExternalReference::keyed_lookup_cache_field_offsets(masm->isolate());
 
-  // Hit on second entry.
-  __ add(ecx, Immediate(1));
-  __ mov(edi,
-         Operand::StaticArray(ecx, times_pointer_size, cache_field_offsets));
-  __ movzx_b(ecx, FieldOperand(ebx, Map::kInObjectPropertiesOffset));
-  __ sub(edi, ecx);
-  __ j(above_equal, &property_array_property);
-  __ jmp(&load_in_object_property);
-
-  // Hit on first entry.
-  __ bind(&hit_on_first_entry);
-  __ mov(edi,
-         Operand::StaticArray(ecx, times_pointer_size, cache_field_offsets));
-  __ movzx_b(ecx, FieldOperand(ebx, Map::kInObjectPropertiesOffset));
-  __ sub(edi, ecx);
-  __ j(above_equal, &property_array_property);
+  // Hit on nth entry.
+  for (int i = kEntriesPerBucket - 1; i >= 0; i--) {
+    __ bind(&hit_on_nth_entry[i]);
+    if (i != 0) {
+      __ add(ecx, Immediate(i));
+    }
+    __ mov(edi,
+           Operand::StaticArray(ecx, times_pointer_size, cache_field_offsets));
+    __ movzx_b(ecx, FieldOperand(ebx, Map::kInObjectPropertiesOffset));
+    __ sub(edi, ecx);
+    __ j(above_equal, &property_array_property);
+    if (i != 0) {
+      __ jmp(&load_in_object_property);
+    }
+  }
 
   // Load in-object property.
   __ bind(&load_in_object_property);
   __ movzx_b(ecx, FieldOperand(ebx, Map::kInstanceSizeOffset));
   __ add(ecx, edi);
   __ mov(eax, FieldOperand(edx, ecx, times_pointer_size, 0));
   __ IncrementCounter(counters->keyed_load_generic_lookup_cache(), 1);
   __ ret(0);
 
   // Load property array property.
@@ skipping 1111 matching lines @@
   Condition cc = *jmp_address == Assembler::kJncShortOpcode
       ? not_zero
       : zero;
   *jmp_address = static_cast<byte>(Assembler::kJccShortPrefix | cc);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32