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Posted to commits@tvm.apache.org by GitBox <gi...@apache.org> on 2020/07/23 03:03:15 UTC
[GitHub] [incubator-tvm] roastduck commented on a change in pull request #6066: [TIR][Transform] HoistIfThenElse added
roastduck commented on a change in pull request #6066:
URL: https://github.com/apache/incubator-tvm/pull/6066#discussion_r459188187
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File path: src/tir/transforms/hoist_if_then_else.cc
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@@ -0,0 +1,376 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*!
+ * \file hoist_if_then_else.cc
+ */
+#include <tvm/arith/analyzer.h>
+#include <tvm/runtime/registry.h>
+#include <tvm/tir/expr.h>
+#include <tvm/tir/stmt_functor.h>
+#include <tvm/tir/transform.h>
+
+#include <queue>
+#include <unordered_map>
+#include <unordered_set>
+
+#include "../../arith/interval_set.h"
+#include "../../runtime/thread_storage_scope.h"
+#include "ir_util.h"
+
+namespace tvm {
+namespace tir {
+
+using VarForMap = std::unordered_map<const Object*, const Object*>;
Review comment:
Can we use explicit types here? For example `std::unordered_map<const VarNode*, const ForNode*>`.
##########
File path: src/tir/transforms/hoist_if_then_else.cc
##########
@@ -0,0 +1,376 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*!
+ * \file hoist_if_then_else.cc
+ */
+#include <tvm/arith/analyzer.h>
+#include <tvm/runtime/registry.h>
+#include <tvm/tir/expr.h>
+#include <tvm/tir/stmt_functor.h>
+#include <tvm/tir/transform.h>
+
+#include <queue>
+#include <unordered_map>
+#include <unordered_set>
+
+#include "../../arith/interval_set.h"
+#include "../../runtime/thread_storage_scope.h"
+#include "ir_util.h"
+
+namespace tvm {
+namespace tir {
+
+using VarForMap = std::unordered_map<const Object*, const Object*>;
+using HoistForIfTuple = std::tuple<bool, const ForNode*, const IfThenElseNode*>;
+
+/*
+ * This pass tries to hoist IfThenElse stmt out of For loop if condition is loop invariant.
+ * For example, given the following block:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * for (k = 0; k < 5; k++)
+ * if (likely(i*2 < 4))
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * We first detect all IfThenElse stmt and find the corresponding loop invariant For stmt.
+ * Then we hoist IfThenElse stmt by one For stmt each step:
+ *
+ * Step 1:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * if (likely(i*2 < 4))
+ * for (k = 0; k < 5; k++)
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * Step 2:
+ * for (i = 0; i < 3; i++)
+ * if (likely(i*2 < 4))
+ * for (j = 0; j < 4; j++)
+ * for (k = 0; k < 5; k++)
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * In this pass, we only continue detecting possible hoisting chance when visiting For,
+ * IfThenElse or AttrStmt Node. For example, for the following block:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * A[i + j] = A[i + j] - 1
+ * for (k = 0; k < 5; k++)
+ * if (likely(i*2 < 4))
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * Only the For with k variable will be considered and the resulting stmt would be:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * A[i + j] = A[i + j] - 1
+ * if (likely(i*2 < 4))
+ * for (k = 0; k < 5; k++)
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * This pass doesn't do hoisting for consecutive IfThenElse stmt. The following
+ * block won't be optimized:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * for (k = 0; k < 5; k++)
+ * if (likely(i*2 < 4))
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ * if (likely(j > 2))
+ * A[i+j+k] = B[i+j+k]
+ *
+ */
+
+// Select potential candidate IRs that can be hoisted.
+class HoistCandidateSelector final : public StmtExprVisitor {
+ public:
+ HoistCandidateSelector() { InitRecorder(); }
+
+ void VisitStmt_(const ForNode* op) final {
+ // Check if it is first for loop, then start the recorder
+ if (!RecordingComplete()) {
+ StartOrAddRecord(op);
+ StmtExprVisitor::VisitStmt_(op);
+ RemoveRecord(op);
+ return;
+ }
+
+ StmtExprVisitor::VisitStmt_(op);
+ }
+
+ void VisitStmt_(const SeqStmtNode* op) final {
+ // If SeqStmt is encountered in the middle of recording
+ // then need to purge all, as it can not be hoisted
+ if (IsRecordingOn()) {
+ ResetRecorder();
+ }
+ StmtExprVisitor::VisitStmt_(op);
+ }
+
+ void VisitStmt_(const AttrStmtNode* op) final {
+ // Maintain list of all vars in AttrStmt
+ // To stop hoisting if any of the block variables are used.
+ //
+ // NOTE: If in future
+ // hoisting is required for any specific case,
+ // then add exception to only those case
+ // rather than allowing for all.
+ UpdateAttrVarList(op);
+ StmtExprVisitor::VisitStmt_(op);
+ RemoveAttrVarList(op);
Review comment:
Does this function mean if there are any variables defined in an `attr` in the condition of an `if`, then that `if` will not be hoisted? Can we only stop hoisting if the `attr` is inside the out-most for loop? Since the `threadIdx` or `blockIdx` `attr` is very commonly used in `if`s, and these `attr`s are outside of all the loops, so they should not block the hoisting.
##########
File path: src/tir/transforms/hoist_if_then_else.cc
##########
@@ -0,0 +1,376 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*!
+ * \file hoist_if_then_else.cc
+ */
+#include <tvm/arith/analyzer.h>
+#include <tvm/runtime/registry.h>
+#include <tvm/tir/expr.h>
+#include <tvm/tir/stmt_functor.h>
+#include <tvm/tir/transform.h>
+
+#include <queue>
+#include <unordered_map>
+#include <unordered_set>
+
+#include "../../arith/interval_set.h"
+#include "../../runtime/thread_storage_scope.h"
+#include "ir_util.h"
+
+namespace tvm {
+namespace tir {
+
+using VarForMap = std::unordered_map<const Object*, const Object*>;
+using HoistForIfTuple = std::tuple<bool, const ForNode*, const IfThenElseNode*>;
+
+/*
+ * This pass tries to hoist IfThenElse stmt out of For loop if condition is loop invariant.
+ * For example, given the following block:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * for (k = 0; k < 5; k++)
+ * if (likely(i*2 < 4))
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * We first detect all IfThenElse stmt and find the corresponding loop invariant For stmt.
+ * Then we hoist IfThenElse stmt by one For stmt each step:
+ *
+ * Step 1:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * if (likely(i*2 < 4))
+ * for (k = 0; k < 5; k++)
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * Step 2:
+ * for (i = 0; i < 3; i++)
+ * if (likely(i*2 < 4))
+ * for (j = 0; j < 4; j++)
+ * for (k = 0; k < 5; k++)
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * In this pass, we only continue detecting possible hoisting chance when visiting For,
+ * IfThenElse or AttrStmt Node. For example, for the following block:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * A[i + j] = A[i + j] - 1
+ * for (k = 0; k < 5; k++)
+ * if (likely(i*2 < 4))
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * Only the For with k variable will be considered and the resulting stmt would be:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * A[i + j] = A[i + j] - 1
+ * if (likely(i*2 < 4))
+ * for (k = 0; k < 5; k++)
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ *
+ * This pass doesn't do hoisting for consecutive IfThenElse stmt. The following
+ * block won't be optimized:
+ * for (i = 0; i < 3; i++)
+ * for (j = 0; j < 4; j++)
+ * for (k = 0; k < 5; k++)
+ * if (likely(i*2 < 4))
+ * A[3*i+2j+k] = B[7*i+3j+k]
+ * if (likely(j > 2))
+ * A[i+j+k] = B[i+j+k]
+ *
+ */
+
+// Select potential candidate IRs that can be hoisted.
+class HoistCandidateSelector final : public StmtExprVisitor {
+ public:
+ HoistCandidateSelector() { InitRecorder(); }
+
+ void VisitStmt_(const ForNode* op) final {
+ // Check if it is first for loop, then start the recorder
+ if (!RecordingComplete()) {
+ StartOrAddRecord(op);
+ StmtExprVisitor::VisitStmt_(op);
+ RemoveRecord(op);
+ return;
+ }
+
+ StmtExprVisitor::VisitStmt_(op);
+ }
+
+ void VisitStmt_(const SeqStmtNode* op) final {
+ // If SeqStmt is encountered in the middle of recording
+ // then need to purge all, as it can not be hoisted
+ if (IsRecordingOn()) {
+ ResetRecorder();
+ }
+ StmtExprVisitor::VisitStmt_(op);
+ }
+
+ void VisitStmt_(const AttrStmtNode* op) final {
+ // Maintain list of all vars in AttrStmt
+ // To stop hoisting if any of the block variables are used.
+ //
+ // NOTE: If in future
+ // hoisting is required for any specific case,
+ // then add exception to only those case
+ // rather than allowing for all.
+ UpdateAttrVarList(op);
+ StmtExprVisitor::VisitStmt_(op);
+ RemoveAttrVarList(op);
+ }
+
+ void VisitStmt_(const IfThenElseNode* op) final {
+ if (IsRecordingOn()) {
+ is_if_cond = true;
+ StmtExprVisitor::VisitExpr(op->condition);
+ is_if_cond = false;
+
+ if (CheckValidIf()) {
+ // Check corresponding for loop
+ bool match_found = false;
+ size_t match_for_loop_pos = 0;
+ for (auto var : if_var_list_) {
+ for (size_t i = 0; i < ordered_for_list_.size() - 1; ++i) {
+ if (ordered_for_list_[i] == var_for_map_[var]) {
+ if (match_for_loop_pos < i) {
+ match_for_loop_pos = i;
+ }
+ match_found = true;
+ break;
+ }
+ }
+ }
+ // If none of the for loop has the matching loop variable as if condition,
+ // then the if node need to be hoisted on top of all, provided no parent loop exists.
+ int target_for_pos = match_found ? match_for_loop_pos + 1 : 0;
+
+ // Check if target for loop is not the parent of current if node
+ if (!IsParentForLoop(target_for_pos)) {
Review comment:
I didn't figure out in which case `target_for_pos` found above would not be a parent. Could you add some more comments here?
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