// Copyright 2014 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/compiler/value-numbering-reducer.h" #include <cstring> #include "src/base/functional.h" #include "src/compiler/node.h" namespace v8 { namespace internal { namespace compiler { namespace { size_t HashCode(Node* node) { size_t h = base::hash_combine(node->op()->HashCode(), node->InputCount()); for (int j = 0; j < node->InputCount(); ++j) { h = base::hash_combine(h, node->InputAt(j)->id()); } return h; } bool Equals(Node* a, Node* b) { DCHECK_NOT_NULL(a); DCHECK_NOT_NULL(b); DCHECK_NOT_NULL(a->op()); DCHECK_NOT_NULL(b->op()); if (!a->op()->Equals(b->op())) return false; if (a->InputCount() != b->InputCount()) return false; for (int j = 0; j < a->InputCount(); ++j) { DCHECK_NOT_NULL(a->InputAt(j)); DCHECK_NOT_NULL(b->InputAt(j)); if (a->InputAt(j)->id() != b->InputAt(j)->id()) return false; } return true; } } // namespace ValueNumberingReducer::ValueNumberingReducer(Zone* zone) : entries_(nullptr), capacity_(0), size_(0), zone_(zone) {} ValueNumberingReducer::~ValueNumberingReducer() {} Reduction ValueNumberingReducer::Reduce(Node* node) { if (!node->op()->HasProperty(Operator::kIdempotent)) return NoChange(); const size_t hash = HashCode(node); if (!entries_) { DCHECK(size_ == 0); DCHECK(capacity_ == 0); // Allocate the initial entries and insert the first entry. capacity_ = kInitialCapacity; entries_ = zone()->NewArray<Node*>(kInitialCapacity); memset(entries_, 0, sizeof(*entries_) * kInitialCapacity); entries_[hash & (kInitialCapacity - 1)] = node; size_ = 1; return NoChange(); } DCHECK(size_ < capacity_); DCHECK(size_ * kCapacityToSizeRatio < capacity_); const size_t mask = capacity_ - 1; size_t dead = capacity_; for (size_t i = hash & mask;; i = (i + 1) & mask) { Node* entry = entries_[i]; if (!entry) { if (dead != capacity_) { // Reuse dead entry that we discovered on the way. entries_[dead] = node; } else { // Have to insert a new entry. entries_[i] = node; size_++; // Resize to keep load factor below 1/kCapacityToSizeRatio. if (size_ * kCapacityToSizeRatio >= capacity_) Grow(); } DCHECK(size_ * kCapacityToSizeRatio < capacity_); return NoChange(); } if (entry == node) { // We need to check for a certain class of collisions here. Imagine the // following scenario: // // 1. We insert node1 with op1 and certain inputs at index i. // 2. We insert node2 with op2 and certain inputs at index i+1. // 3. Some other reducer changes node1 to op2 and the inputs from node2. // // Now we are called again to reduce node1, and we would return NoChange // in this case because we find node1 first, but what we should actually // do is return Replace(node2) instead. for (size_t j = (i + 1) & mask;; j = (j + 1) & mask) { Node* entry = entries_[j]; if (!entry) { // No collision, {node} is fine. return NoChange(); } if (entry->IsDead()) { continue; } if (Equals(entry, node)) { // Overwrite the colliding entry with the actual entry. entries_[i] = entry; return Replace(entry); } } } // Skip dead entries, but remember their indices so we can reuse them. if (entry->IsDead()) { dead = i; continue; } if (Equals(entry, node)) { return Replace(entry); } } } void ValueNumberingReducer::Grow() { // Allocate a new block of entries kCapacityToSizeRatio times the previous // capacity. Node** const old_entries = entries_; size_t const old_capacity = capacity_; capacity_ *= kCapacityToSizeRatio; entries_ = zone()->NewArray<Node*>(capacity_); memset(entries_, 0, sizeof(*entries_) * capacity_); size_ = 0; size_t const mask = capacity_ - 1; // Insert the old entries into the new block (skipping dead nodes). for (size_t i = 0; i < old_capacity; ++i) { Node* const old_entry = old_entries[i]; if (!old_entry || old_entry->IsDead()) continue; for (size_t j = HashCode(old_entry) & mask;; j = (j + 1) & mask) { Node* const entry = entries_[j]; if (entry == old_entry) { // Skip duplicate of the old entry. break; } if (!entry) { entries_[j] = old_entry; size_++; break; } } } } } // namespace compiler } // namespace internal } // namespace v8