Further robustify the keyed lookup cache against unlucky hash

src/mips/ic-mips.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 1020 matching lines @@
   __ lw(a2, FieldMemOperand(a1, HeapObject::kMapOffset));
   __ sra(a3, a2, KeyedLookupCache::kMapHashShift);
   __ lw(t0, FieldMemOperand(a0, String::kHashFieldOffset));
   __ sra(at, t0, String::kHashShift);
   __ xor_(a3, a3, at);
   int mask = KeyedLookupCache::kCapacityMask & KeyedLookupCache::kHashMask;
   __ And(a3, a3, Operand(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(isolate);
   __ li(t0, Operand(cache_keys));
   __ sll(at, a3, kPointerSizeLog2 + 1);
   __ addu(t0, t0, at);
-  __ lw(t1, MemOperand(t0));
-  __ Branch(&try_second_entry, ne, a2, Operand(t1));
-  __ lw(t1, MemOperand(t0, kPointerSize));
-  __ Branch(&hit_on_first_entry, eq, a0, Operand(t1));
 
-  __ bind(&try_second_entry);
-  __ lw(t1, MemOperand(t0, kPointerSize * 2));
+  for (int i = 0; i < kEntriesPerBucket - 1; i++) {
+    Label try_next_entry;
+    __ lw(t1, MemOperand(t0, kPointerSize * i * 2));
+    __ Branch(&try_next_entry, ne, a2, Operand(t1));
+    __ lw(t1, MemOperand(t0, kPointerSize * (i * 2 + 1)));
+    __ Branch(&hit_on_nth_entry[i], eq, a0, Operand(t1));
+    __ bind(&try_next_entry);
+  }
+
+  __ lw(t1, MemOperand(t0, kPointerSize * (kEntriesPerBucket - 1) * 2));
   __ Branch(&slow, ne, a2, Operand(t1));
-  __ lw(t1, MemOperand(t0, kPointerSize * 3));
+  __ lw(t1, MemOperand(t0, kPointerSize * ((kEntriesPerBucket - 1) * 2 + 1)));
   __ Branch(&slow, ne, a0, Operand(t1));
 
   // Get field offset.
   // a0     : key
   // a1     : receiver
   // a2     : receiver's map
   // a3     : lookup cache index
   ExternalReference cache_field_offsets =
       ExternalReference::keyed_lookup_cache_field_offsets(isolate);
 
-  // Hit on second entry.
-  __ li(t0, Operand(cache_field_offsets));
-  __ sll(at, a3, kPointerSizeLog2);
-  __ addu(at, t0, at);
-  __ lw(t1, MemOperand(at, kPointerSize));
-  __ lbu(t2, FieldMemOperand(a2, Map::kInObjectPropertiesOffset));
-  __ Subu(t1, t1, t2);
-  __ Branch(&property_array_property, ge, t1, Operand(zero_reg));
-  __ Branch(&load_in_object_property);
-
-  // Hit on first entry.
-  __ bind(&hit_on_first_entry);
-  __ li(t0, Operand(cache_field_offsets));
-  __ sll(at, a3, kPointerSizeLog2);
-  __ addu(at, t0, at);
-  __ lw(t1, MemOperand(at));
-  __ lbu(t2, FieldMemOperand(a2, Map::kInObjectPropertiesOffset));
-  __ Subu(t1, t1, t2);
-  __ Branch(&property_array_property, ge, t1, Operand(zero_reg));
+  // Hit on nth entry.
+  for (int i = kEntriesPerBucket - 1; i >= 0; i--) {
+    __ bind(&hit_on_nth_entry[i]);
+    __ li(t0, Operand(cache_field_offsets));
+    __ sll(at, a3, kPointerSizeLog2);
+    __ addu(at, t0, at);
+    __ lw(t1, MemOperand(at, kPointerSize * i));
+    __ lbu(t2, FieldMemOperand(a2, Map::kInObjectPropertiesOffset));
+    __ Branch(&property_array_property, ge, t1, Operand(zero_reg));
+    if (i != 0) {
+      __ Branch(&load_in_object_property);
+    }
+  }
 
   // Load in-object property.
   __ bind(&load_in_object_property);
   __ lbu(t2, FieldMemOperand(a2, Map::kInstanceSizeOffset));
   __ addu(t2, t2, t1);  // Index from start of object.
   __ Subu(a1, a1, Operand(kHeapObjectTag));  // Remove the heap tag.
   __ sll(at, t2, kPointerSizeLog2);
   __ addu(at, a1, at);
   __ lw(v0, MemOperand(at));
   __ IncrementCounter(isolate->counters()->keyed_load_generic_lookup_cache(),
@@ skipping 605 matching lines @@
     Register reg = Register::from_code(Assembler::GetRs(instr_at_patch));
     patcher.masm()->andi(at, reg, kSmiTagMask);
     patcher.ChangeBranchCondition(eq);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS