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[RELAY][PASS] Common subexpression elimination (#2639)
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/*! | ||
* Copyright (c) 2019 by Contributors | ||
* | ||
* \file eliminate_common_subexpr.cc | ||
* \brief Combine common subexpressions. | ||
* | ||
* This is an optimization pass that eliminates common subexpressions. During the pass, it tries | ||
* to replace an expression with a previously appeared expression with the same input and | ||
* attributes. The fskip callback argument allows us to skip specific expressions. | ||
*/ | ||
#include <tvm/relay/pass.h> | ||
#include <tvm/relay/expr_functor.h> | ||
#include <unordered_map> | ||
#include "./pattern_util.h" | ||
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namespace tvm { | ||
namespace relay { | ||
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class CommonSubexprEliminator : public ExprMutator { | ||
public: | ||
explicit CommonSubexprEliminator(runtime::TypedPackedFunc<bool(Expr)> fskip): fskip_(fskip) {} | ||
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Expr VisitExpr_(const CallNode* call) final { | ||
static auto op_stateful = Op::GetAttr<TOpIsStateful>("TOpIsStateful"); | ||
Expr new_expr = ExprMutator::VisitExpr_(call); | ||
const CallNode* new_call = new_expr.as<CallNode>(); | ||
CHECK(new_call); | ||
const OpNode* op = new_call->op.as<OpNode>(); | ||
AttrsEqual attrs_equal; | ||
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if (new_call->args.size() == 0 || op == nullptr || op_stateful.get(GetRef<Op>(op), false)) { | ||
return new_expr; | ||
} | ||
if (fskip_ != nullptr && fskip_(new_expr)) { | ||
return new_expr; | ||
} | ||
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auto it = expr_map_.find(new_call->op); | ||
if (it != expr_map_.end()) { | ||
for (const CallNode* candidate : it->second) { | ||
bool is_equivalent = true; | ||
if (!attrs_equal(new_call->attrs, candidate->attrs)) { | ||
continue; | ||
} | ||
for (size_t i = 0; i < new_call->args.size(); i++) { | ||
if (!new_call->args[i].same_as(candidate->args[i]) && | ||
!IsEqualScalar(new_call->args[i], candidate->args[i])) { | ||
is_equivalent = false; | ||
break; | ||
} | ||
} | ||
if (!is_equivalent) continue; | ||
return GetRef<Call>(candidate); | ||
} | ||
} | ||
expr_map_[new_call->op].push_back(new_call); | ||
return new_expr; | ||
} | ||
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std::unordered_map<Expr, std::vector<const CallNode*>, NodeHash, NodeEqual> expr_map_; | ||
runtime::TypedPackedFunc<bool(Expr)> fskip_; | ||
}; | ||
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Expr EliminateCommonSubexpr(const Expr& expr, PackedFunc callback) { | ||
return CommonSubexprEliminator(callback)(expr); | ||
} | ||
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TVM_REGISTER_API("relay._ir_pass.eliminate_common_subexpr") | ||
.set_body_typed<Expr(Expr, PackedFunc)>(EliminateCommonSubexpr); | ||
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} // namespace relay | ||
} // namespace tvm |
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"""Test eliminate common subexpr pass""" | ||
from tvm import relay | ||
from tvm.relay.op import register_alter_op_layout | ||
from tvm.relay import ir_pass | ||
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def test_simple(): | ||
def before(): | ||
x = relay.var("x", shape=(1, 16)) | ||
y1 = relay.nn.relu(x) | ||
y2 = relay.nn.relu(x) | ||
y1 = relay.add(y1, relay.const(1.0, "float32")) | ||
y2 = relay.add(y2, relay.const(1.0, "float32")) | ||
y = relay.add(y1, y2) | ||
f = relay.Function([x], y) | ||
return f | ||
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def expected(): | ||
x = relay.var("x", shape=(1, 16)) | ||
y = relay.nn.relu(x) | ||
y = relay.add(y, relay.const(1.0, "float32")) | ||
y = relay.add(y, y) | ||
f = relay.Function([x], y) | ||
return f | ||
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z = before() | ||
z = ir_pass.eliminate_common_subexpr(z) | ||
assert ir_pass.alpha_equal(z, expected()) | ||
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def test_callback(): | ||
def before(): | ||
x = relay.var("x", shape=(1, 16)) | ||
y1 = relay.nn.relu(x) | ||
y2 = relay.nn.relu(x) | ||
y1 = relay.add(y1, relay.const(1.0, "float32")) | ||
y2 = relay.add(y2, relay.const(1.0, "float32")) | ||
y = relay.add(y1, y2) | ||
f = relay.Function([x], y) | ||
return f | ||
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def expected(): | ||
x = relay.var("x", shape=(1, 16)) | ||
y = relay.nn.relu(x) | ||
y1 = relay.add(y, relay.const(1.0, "float32")) | ||
y2 = relay.add(y, relay.const(1.0, "float32")) | ||
y = relay.add(y1, y2) | ||
f = relay.Function([x], y) | ||
return f | ||
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def fskip(expr): | ||
if isinstance(expr, relay.expr.Call) and expr.op.name == 'add': | ||
return True | ||
return False | ||
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z = before() | ||
z = ir_pass.eliminate_common_subexpr(z, fskip) | ||
assert ir_pass.alpha_equal(z, expected()) | ||
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if __name__ == "__main__": | ||
test_simple() | ||
test_callback() |