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#include <torch/csrc/jit/passes/constant_pooling.h>
#include <ATen/core/symbol.h>
#include <torch/csrc/jit/ir/alias_analysis.h>
#include <torch/csrc/jit/ir/ir.h>
#include <torch/csrc/jit/ir/node_hashing.h>
#include <unordered_set>
namespace torch {
namespace jit {
namespace {
// Very similar to the common subexpression elimination pass
// Move all constants to the beginning of the graph, and deduplicate
void ConstantPooling(
Block* block,
std::unordered_set<Node*, HashNode, EqualNode>& constants,
const AliasDb& aliasDb) {
for (auto it = block->nodes().begin(); it != block->nodes().end();) {
auto node = *it;
// node may be moved to a different block so advance iterator now
++it;
if (!node->blocks().empty()) {
// Traverse sub-blocks.
for (auto block : node->blocks()) {
ConstantPooling(block, constants, aliasDb);
}
continue;
}
if (node->kind() != prim::Constant) {
continue;
}
// Check whether the same constant already exists.
auto subit = constants.insert(node);
if (!subit.second) {
auto existing = *subit.first;
auto old_ivalue = toIValue(existing->output());
auto new_ivalue = toIValue(node->output());
// if both values are the same object, we do not need to worry about
// changing the aliasing relationship
bool same_identity =
(old_ivalue && new_ivalue && (old_ivalue->is(new_ivalue)));
if (!same_identity &&
!aliasDb.safeToChangeAliasingRelationship(
node->outputs(), existing->outputs())) {
continue;
}
// constant exists, replace the uses of node, and destroy it.
node->replaceAllUsesWith(existing);
node->destroy();
continue;
}
// Move the constant definition to the beginning of the graph.
auto first_node = node->owningGraph()->block()->nodes().front();
if (node != first_node)
node->moveBefore(first_node);
}
}
} // anonymous namespace
void ConstantPooling(const std::shared_ptr<Graph>& graph) {
AliasDb aliasDb(graph);
std::unordered_set<Node*, HashNode, EqualNode> constants;
ConstantPooling(graph->block(), constants, aliasDb);
}
} // namespace jit
} // namespace torch
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