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// 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-properties.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* temp_zone, Zone* graph_zone)
: entries_(nullptr),
capacity_(0),
size_(0),
temp_zone_(temp_zone),
graph_zone_(graph_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_ = temp_zone()->NewArray<Node*>(kInitialCapacity);
memset(entries_, 0, sizeof(*entries_) * kInitialCapacity);
entries_[hash & (kInitialCapacity - 1)] = node;
size_ = 1;
return NoChange();
}
DCHECK(size_ < capacity_);
DCHECK(size_ + size_ / 4 < 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 80%
if (size_ + size_ / 4 >= capacity_) Grow();
}
DCHECK(size_ + size_ / 4 < 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 (entry == node) {
// Collision with ourselves, doesn't count as a real collision.
// Opportunistically clean-up the duplicate entry if we're at the end
// of a bucket.
if (!entries_[(j + 1) & mask]) {
entries_[j] = nullptr;
size_--;
return NoChange();
}
// Otherwise, keep searching for another collision.
continue;
}
if (Equals(entry, node)) {
Reduction reduction = ReplaceIfTypesMatch(node, entry);
if (reduction.Changed()) {
// Overwrite the colliding entry with the actual entry.
entries_[i] = entry;
// Opportunistically clean-up the duplicate entry if we're at the
// end of a bucket.
if (!entries_[(j + 1) & mask]) {
entries_[j] = nullptr;
size_--;
}
}
return reduction;
}
}
}
// Skip dead entries, but remember their indices so we can reuse them.
if (entry->IsDead()) {
dead = i;
continue;
}
if (Equals(entry, node)) {
return ReplaceIfTypesMatch(node, entry);
}
}
}
Reduction ValueNumberingReducer::ReplaceIfTypesMatch(Node* node,
Node* replacement) {
// Make sure the replacement has at least as good type as the original node.
if (NodeProperties::IsTyped(replacement) && NodeProperties::IsTyped(node)) {
Type* replacement_type = NodeProperties::GetType(replacement);
Type* node_type = NodeProperties::GetType(node);
if (!replacement_type->Is(node_type)) {
// Ideally, we would set an intersection of {replacement_type} and
// {node_type} here. However, typing of NumberConstants assigns different
// types to constants with the same value (it creates a fresh heap
// number), which would make the intersection empty. To be safe, we use
// the smaller type if the types are comparable.
if (node_type->Is(replacement_type)) {
NodeProperties::SetType(replacement, node_type);
} else {
// Types are not comparable => do not replace.
return NoChange();
}
}
}
return Replace(replacement);
}
void ValueNumberingReducer::Grow() {
// Allocate a new block of entries double the previous capacity.
Node** const old_entries = entries_;
size_t const old_capacity = capacity_;
capacity_ *= 2;
entries_ = temp_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
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