Further robustify the keyed lookup cache against unlucky hash

src/x64/ic-x64.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 449 matching lines @@
   __ movl(rcx, rbx);
   __ shr(rcx, Immediate(KeyedLookupCache::kMapHashShift));
   __ movl(rdi, FieldOperand(rax, String::kHashFieldOffset));
   __ shr(rdi, Immediate(String::kHashShift));
   __ xor_(rcx, rdi);
   int mask = (KeyedLookupCache::kCapacityMask & KeyedLookupCache::kHashMask);
   __ and_(rcx, Immediate(mask));
 
   // 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());
-  __ movq(rdi, rcx);
-  __ shl(rdi, Immediate(kPointerSizeLog2 + 1));
-  __ LoadAddress(kScratchRegister, cache_keys);
-  __ cmpq(rbx, Operand(kScratchRegister, rdi, times_1, 0));
-  __ j(not_equal, &try_second_entry);
-  __ cmpq(rax, Operand(kScratchRegister, rdi, times_1, kPointerSize));
-  __ j(equal, &hit_on_first_entry);
 
-  __ bind(&try_second_entry);
-  __ cmpq(rbx, Operand(kScratchRegister, rdi, times_1, kPointerSize * 2));
+  for (int i = 0; i < kEntriesPerBucket - 1; i++) {
+    Label try_next_entry;
+    __ movq(rdi, rcx);
+    __ shl(rdi, Immediate(kPointerSizeLog2 + 1));
+    __ LoadAddress(kScratchRegister, cache_keys);
+    int off = kPointerSize * i * 2;
+    __ cmpq(rbx, Operand(kScratchRegister, rdi, times_1, off));
+    __ j(not_equal, &try_next_entry);
+    __ cmpq(rax, Operand(kScratchRegister, rdi, times_1, off + kPointerSize));
+    __ j(equal, &hit_on_nth_entry[i]);
+    __ bind(&try_next_entry);
+  }
+
+  int off = kPointerSize * (kEntriesPerBucket - 1) * 2;
+  __ cmpq(rbx, Operand(kScratchRegister, rdi, times_1, off));
   __ j(not_equal, &slow);
-  __ cmpq(rax, Operand(kScratchRegister, rdi, times_1, kPointerSize * 3));
+  __ cmpq(rax, Operand(kScratchRegister, rdi, times_1, off + kPointerSize));
   __ j(not_equal, &slow);
 
   // Get field offset, which is a 32-bit integer.
   ExternalReference cache_field_offsets
       = ExternalReference::keyed_lookup_cache_field_offsets(masm->isolate());
 
-  // Hit on second entry.
-  __ LoadAddress(kScratchRegister, cache_field_offsets);
-  __ addl(rcx, Immediate(1));
-  __ movl(rdi, Operand(kScratchRegister, rcx, times_4, 0));
-  __ movzxbq(rcx, FieldOperand(rbx, Map::kInObjectPropertiesOffset));
-  __ subq(rdi, rcx);
-  __ j(above_equal, &property_array_property);
-  __ jmp(&load_in_object_property);
-
-  // Hit on first entry.
-  __ bind(&hit_on_first_entry);
-  __ LoadAddress(kScratchRegister, cache_field_offsets);
-  __ movl(rdi, Operand(kScratchRegister, rcx, times_4, 0));
-  __ movzxbq(rcx, FieldOperand(rbx, Map::kInObjectPropertiesOffset));
-  __ subq(rdi, rcx);
-  __ 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) {
+      __ addl(rcx, Immediate(i));
+    }
+    __ LoadAddress(kScratchRegister, cache_field_offsets);
+    __ movl(rdi, Operand(kScratchRegister, rcx, times_4, 0));
+    __ movzxbq(rcx, FieldOperand(rbx, Map::kInObjectPropertiesOffset));
+    __ subq(rdi, rcx);
+    __ j(above_equal, &property_array_property);
+    if (i != 0) {
+      __ jmp(&load_in_object_property);
+    }
+  }
 
   // Load in-object property.
   __ bind(&load_in_object_property);
   __ movzxbq(rcx, FieldOperand(rbx, Map::kInstanceSizeOffset));
   __ addq(rcx, rdi);
   __ movq(rax, FieldOperand(rdx, rcx, times_pointer_size, 0));
   __ IncrementCounter(counters->keyed_load_generic_lookup_cache(), 1);
   __ ret(0);
 
   // Load property array property.
@@ skipping 1202 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_X64