// 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. #include "src/ic/stub-cache.h" #include "src/ast/ast.h" #include "src/base/bits.h" #include "src/counters.h" #include "src/heap/heap.h" #include "src/ic/ic-inl.h" namespace v8 { namespace internal { StubCache::StubCache(Isolate* isolate) : isolate_(isolate) { // Ensure the nullptr (aka Smi::kZero) which StubCache::Get() returns // when the entry is not found is not considered as a handler. DCHECK(!IC::IsHandler(nullptr)); } void StubCache::Initialize() { DCHECK(base::bits::IsPowerOfTwo(kPrimaryTableSize)); DCHECK(base::bits::IsPowerOfTwo(kSecondaryTableSize)); Clear(); } // Hash algorithm for the primary table. This algorithm is replicated in // assembler for every architecture. Returns an index into the table that // is scaled by 1 << kCacheIndexShift. int StubCache::PrimaryOffset(Name* name, Map* map) { STATIC_ASSERT(kCacheIndexShift == Name::kHashShift); // Compute the hash of the name (use entire hash field). DCHECK(name->HasHashCode()); uint32_t field = name->hash_field(); // Using only the low bits in 64-bit mode is unlikely to increase the // risk of collision even if the heap is spread over an area larger than // 4Gb (and not at all if it isn't). uint32_t map_low32bits = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(map)); // Base the offset on a simple combination of name and map. uint32_t key = map_low32bits + field; return key & ((kPrimaryTableSize - 1) << kCacheIndexShift); } // Hash algorithm for the secondary table. This algorithm is replicated in // assembler for every architecture. Returns an index into the table that // is scaled by 1 << kCacheIndexShift. int StubCache::SecondaryOffset(Name* name, int seed) { // Use the seed from the primary cache in the secondary cache. uint32_t name_low32bits = static_cast<uint32_t>(reinterpret_cast<uintptr_t>(name)); uint32_t key = (seed - name_low32bits) + kSecondaryMagic; return key & ((kSecondaryTableSize - 1) << kCacheIndexShift); } #ifdef DEBUG namespace { bool CommonStubCacheChecks(StubCache* stub_cache, Name* name, Map* map, MaybeObject* handler) { // Validate that the name and handler do not move on scavenge, and that we // can use identity checks instead of structural equality checks. DCHECK(!name->GetHeap()->InNewSpace(name)); DCHECK(!name->GetHeap()->InNewSpace(handler)); DCHECK(name->IsUniqueName()); DCHECK(name->HasHashCode()); if (handler) DCHECK(IC::IsHandler(handler)); return true; } } // namespace #endif MaybeObject* StubCache::Set(Name* name, Map* map, MaybeObject* handler) { DCHECK(CommonStubCacheChecks(this, name, map, handler)); // Compute the primary entry. int primary_offset = PrimaryOffset(name, map); Entry* primary = entry(primary_, primary_offset); MaybeObject* old_handler = primary->value; // If the primary entry has useful data in it, we retire it to the // secondary cache before overwriting it. if (old_handler != MaybeObject::FromObject( isolate_->builtins()->builtin(Builtins::kIllegal))) { Map* old_map = primary->map; int seed = PrimaryOffset(primary->key, old_map); int secondary_offset = SecondaryOffset(primary->key, seed); Entry* secondary = entry(secondary_, secondary_offset); *secondary = *primary; } // Update primary cache. primary->key = name; primary->value = handler; primary->map = map; isolate()->counters()->megamorphic_stub_cache_updates()->Increment(); return handler; } MaybeObject* StubCache::Get(Name* name, Map* map) { DCHECK(CommonStubCacheChecks(this, name, map, nullptr)); int primary_offset = PrimaryOffset(name, map); Entry* primary = entry(primary_, primary_offset); if (primary->key == name && primary->map == map) { return primary->value; } int secondary_offset = SecondaryOffset(name, primary_offset); Entry* secondary = entry(secondary_, secondary_offset); if (secondary->key == name && secondary->map == map) { return secondary->value; } return nullptr; } void StubCache::Clear() { MaybeObject* empty = MaybeObject::FromObject( isolate_->builtins()->builtin(Builtins::kIllegal)); for (int i = 0; i < kPrimaryTableSize; i++) { primary_[i].key = isolate()->heap()->empty_string(); primary_[i].map = nullptr; primary_[i].value = empty; } for (int j = 0; j < kSecondaryTableSize; j++) { secondary_[j].key = isolate()->heap()->empty_string(); secondary_[j].map = nullptr; secondary_[j].value = empty; } } } // namespace internal } // namespace v8