Further robustify the keyed lookup cache against unlucky hash

src/arm/ic-arm.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 1018 matching lines @@
   // based on 32 bits of the map pointer and the string hash.
   __ ldr(r2, FieldMemOperand(r1, HeapObject::kMapOffset));
   __ mov(r3, Operand(r2, ASR, KeyedLookupCache::kMapHashShift));
   __ ldr(r4, FieldMemOperand(r0, String::kHashFieldOffset));
   __ eor(r3, r3, Operand(r4, ASR, String::kHashShift));
   int mask = KeyedLookupCache::kCapacityMask & KeyedLookupCache::kHashMask;
   __ And(r3, r3, 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);
+
   __ mov(r4, Operand(cache_keys));
   __ add(r4, r4, Operand(r3, LSL, kPointerSizeLog2 + 1));
-  // Move r4 to second entry.
-  __ ldr(r5, MemOperand(r4, kPointerSize * 2, PostIndex));
-  __ cmp(r2, r5);
-  __ b(ne, &try_second_entry);
-  __ ldr(r5, MemOperand(r4, -kPointerSize));  // Load symbol
-  __ cmp(r0, r5);
-  __ b(eq, &hit_on_first_entry);
 
-  __ bind(&try_second_entry);
-  __ ldr(r5, MemOperand(r4, kPointerSize, PostIndex));  // Move r4 to symbol.
+  for (int i = 0; i < kEntriesPerBucket - 1; i++) {
+    Label try_next_entry;
+    // Load map and move r4 to next entry.
+    __ ldr(r5, MemOperand(r4, kPointerSize * 2, PostIndex));
+    __ cmp(r2, r5);
+    __ b(ne, &try_next_entry);
+    __ ldr(r5, MemOperand(r4, -kPointerSize));  // Load symbol
+    __ cmp(r0, r5);
+    __ b(eq, &hit_on_nth_entry[i]);
+    __ bind(&try_next_entry);
+  }
+
+  // Last entry: Load map and move r4 to symbol.
+  __ ldr(r5, MemOperand(r4, kPointerSize, PostIndex));
   __ cmp(r2, r5);
   __ b(ne, &slow);
   __ ldr(r5, MemOperand(r4));
   __ cmp(r0, r5);
   __ b(ne, &slow);
 
   // Get field offset.
   // r0     : key
   // r1     : receiver
   // r2     : receiver's map
   // r3     : lookup cache index
   ExternalReference cache_field_offsets =
       ExternalReference::keyed_lookup_cache_field_offsets(isolate);
 
-  // Hit on second entry.
-  __ mov(r4, Operand(cache_field_offsets));
-  __ add(r3, r3, Operand(1));
-  __ ldr(r5, MemOperand(r4, r3, LSL, kPointerSizeLog2));
-  __ ldrb(r6, FieldMemOperand(r2, Map::kInObjectPropertiesOffset));
-  __ sub(r5, r5, r6, SetCC);
-  __ b(ge, &property_array_property);
-  __ jmp(&load_in_object_property);
-
-  // Hit on first entry.
-  __ bind(&hit_on_first_entry);
-  __ mov(r4, Operand(cache_field_offsets));
-  __ ldr(r5, MemOperand(r4, r3, LSL, kPointerSizeLog2));
-  __ ldrb(r6, FieldMemOperand(r2, Map::kInObjectPropertiesOffset));
-  __ sub(r5, r5, r6, SetCC);
-  __ b(ge, &property_array_property);
+  // Hit on nth entry.
+  for (int i = kEntriesPerBucket - 1; i >= 0; i--) {
+    __ bind(&hit_on_nth_entry[i]);
+    __ mov(r4, Operand(cache_field_offsets));
+    if (i != 0) {
+      __ add(r3, r3, Operand(i));
+    }
+    __ ldr(r5, MemOperand(r4, r3, LSL, kPointerSizeLog2));
+    __ ldrb(r6, FieldMemOperand(r2, Map::kInObjectPropertiesOffset));
+    __ sub(r5, r5, r6, SetCC);
+    __ b(ge, &property_array_property);
+    if (i != 0) {
+      __ jmp(&load_in_object_property);
+    }
+  }
 
   // Load in-object property.
   __ bind(&load_in_object_property);
   __ ldrb(r6, FieldMemOperand(r2, Map::kInstanceSizeOffset));
   __ add(r6, r6, r5);  // Index from start of object.
   __ sub(r1, r1, Operand(kHeapObjectTag));  // Remove the heap tag.
   __ ldr(r0, MemOperand(r1, r6, LSL, kPointerSizeLog2));
   __ IncrementCounter(isolate->counters()->keyed_load_generic_lookup_cache(),
                       1, r2, r3);
   __ Ret();
@@ skipping 609 matching lines @@
     Register reg = Assembler::GetRn(instr_at_patch);
     patcher.masm()->tst(reg, Operand(kSmiTagMask));
     patcher.EmitCondition(eq);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM