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// Copyright 2021 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/wasm-escape-analysis.h"
#include "src/compiler/machine-graph.h"
#include "src/compiler/node-properties.h"
namespace v8 {
namespace internal {
namespace compiler {
Reduction WasmEscapeAnalysis::Reduce(Node* node) {
switch (node->opcode()) {
case IrOpcode::kAllocateRaw:
return ReduceAllocateRaw(node);
default:
return NoChange();
}
}
Reduction WasmEscapeAnalysis::ReduceAllocateRaw(Node* node) {
DCHECK_EQ(node->opcode(), IrOpcode::kAllocateRaw);
// TODO(manoskouk): Account for phis that still have uses.
// Collect all value edges of {node} in this vector.
std::vector<Edge> value_edges;
for (Edge edge : node->use_edges()) {
if (NodeProperties::IsValueEdge(edge)) {
if ((edge.from()->opcode() == IrOpcode::kPhi &&
edge.from()->use_edges().empty()) ||
(edge.index() == 0 &&
(edge.from()->opcode() == IrOpcode::kStoreToObject ||
edge.from()->opcode() == IrOpcode::kInitializeImmutableInObject))) {
// StoreToObject, InitializeImmutableInObject and phis without uses can
// be replaced and do not require the allocation.
value_edges.push_back(edge);
} else {
// Allocation not reducible.
return NoChange();
}
}
}
// Remove all discovered stores from the effect chain.
for (Edge edge : value_edges) {
DCHECK(NodeProperties::IsValueEdge(edge));
Node* use = edge.from();
if (use->opcode() == IrOpcode::kPhi) {
DCHECK(use->use_edges().empty());
// Useless phi. Kill it.
use->Kill();
} else {
DCHECK_EQ(edge.index(), 0);
DCHECK(!use->IsDead());
DCHECK(use->opcode() == IrOpcode::kStoreToObject ||
use->opcode() == IrOpcode::kInitializeImmutableInObject);
// The value stored by this StoreToObject node might be another allocation
// which has no more uses. Therefore we have to revisit it. Note that this
// will not happen automatically: ReplaceWithValue does not trigger
// revisits of former inputs of the replaced node.
Node* stored_value = NodeProperties::GetValueInput(use, 2);
Revisit(stored_value);
ReplaceWithValue(use, mcgraph_->Dead(),
NodeProperties::GetEffectInput(use), mcgraph_->Dead());
use->Kill();
}
}
// Remove the allocation from the effect and control chains.
ReplaceWithValue(node, mcgraph_->Dead(), NodeProperties::GetEffectInput(node),
NodeProperties::GetControlInput(node));
return Changed(node);
}
} // namespace compiler
} // namespace internal
} // namespace v8
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