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Subject [GitHub] [incubator-tvm] tqchen commented on a change in pull request #6667: [ARITH] Introduce iterator (quasi)affine map detection.
Date Wed, 14 Oct 2020 00:26:11 GMT

tqchen commented on a change in pull request #6667:
URL: https://github.com/apache/incubator-tvm/pull/6667#discussion_r504331608



##########
File path: src/arith/iter_affine_map.cc
##########
@@ -0,0 +1,703 @@
+/*
+ * 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 src/arith/iter_affine_map.cc
+ */
+#include <tvm/arith/analyzer.h>
+#include <tvm/arith/iter_affine_map.h>
+#include <tvm/tir/analysis.h>
+#include <tvm/tir/expr.h>
+#include <tvm/tir/expr_functor.h>
+#include <tvm/tir/op.h>
+
+#include "../support/util.h"
+#include "const_fold.h"
+
+namespace tvm {
+namespace arith {
+
+using namespace tir;
+
+IterMark::IterMark(PrimExpr source, PrimExpr extent) {
+  auto n = make_object<IterMarkNode>();
+  n->source = std::move(source);
+  n->extent = std::move(extent);
+  data_ = std::move(n);
+}
+
+TVM_REGISTER_GLOBAL("arith.IterMark").set_body_typed([](PrimExpr source, PrimExpr extent)
{
+  return IterMark(source, extent);
+});
+
+TVM_REGISTER_NODE_TYPE(IterMarkNode);
+
+TVM_STATIC_IR_FUNCTOR(ReprPrinter, vtable)
+    .set_dispatch<IterMarkNode>([](const ObjectRef& node, ReprPrinter* p) {
+      auto* op = static_cast<const IterMarkNode*>(node.get());
+      p->stream << "IterMark(" << op->source << ", extent=" <<
op->extent;
+    });
+
+IterSplitExpr::IterSplitExpr(IterMark source) {
+  auto n = make_object<IterSplitExprNode>();
+  auto one = make_const(source->source->dtype, 1);
+  n->dtype = source->source->dtype;
+  n->source = std::move(source);
+  n->extent = n->source->extent;
+  n->lower_factor = one;
+  n->scale = one;
+  data_ = std::move(n);
+}
+
+IterSplitExpr::IterSplitExpr(IterMark source, PrimExpr lower_factor, PrimExpr extent,
+                             PrimExpr scale) {
+  auto n = make_object<IterSplitExprNode>();
+  n->dtype = source->source->dtype;
+  n->source = std::move(source);
+  n->lower_factor = std::move(lower_factor);
+  n->extent = std::move(extent);
+  n->scale = std::move(scale);
+  data_ = std::move(n);
+}
+
+TVM_REGISTER_GLOBAL("arith.IterSplitExpr")
+    .set_body_typed([](IterMark source, PrimExpr lower_factor, PrimExpr extent, PrimExpr
scale) {
+      return IterSplitExpr(source, lower_factor, extent, scale);
+    });
+
+TVM_REGISTER_NODE_TYPE(IterSplitExprNode);
+
+TVM_STATIC_IR_FUNCTOR(ReprPrinter, vtable)
+    .set_dispatch<IterSplitExprNode>([](const ObjectRef& node, ReprPrinter* p)
{
+      auto* op = static_cast<const IterSplitExprNode*>(node.get());
+      p->stream << "IterSplit(" << op->source << ", lower_factor="
<< op->lower_factor
+                << ", extent=" << op->extent << ", scale=" <<
op->scale;
+    });
+
+IterSumExpr::IterSumExpr(Array<IterSplitExpr> args, PrimExpr base) {
+  auto n = make_object<IterSumExprNode>();
+  n->dtype = base->dtype;
+  n->args = std::move(args);
+  n->base = std::move(base);
+  data_ = std::move(n);
+}
+
+TVM_REGISTER_GLOBAL("arith.IterSumExpr")
+    .set_body_typed([](Array<IterSplitExpr> args, PrimExpr base) {
+      return IterSumExpr(args, base);
+    });
+
+TVM_REGISTER_NODE_TYPE(IterSumExprNode);
+
+TVM_STATIC_IR_FUNCTOR(ReprPrinter, vtable)
+    .set_dispatch<IterSumExprNode>([](const ObjectRef& node, ReprPrinter* p) {
+      auto* op = static_cast<const IterSumExprNode*>(node.get());
+      p->stream << "IterSum(" << op->args << ", " << op->base
<< ")";
+    });
+
+/*!
+ * \brief Util to check if all splits in the sumexpr are
+ *        independent and complete (covers all the original iter space).
+ *
+ */
+class IterMarkSplitCollector {
+ public:
+  // mark all IterMarks that are visited.
+  std::unordered_set<IterMark, ObjectPtrHash, ObjectPtrEqual> visited_;
+  // each iter mark to its outgoing splits that are referenced.
+  std::unordered_map<IterMark, std::vector<IterSplitExpr>, ObjectPtrHash, ObjectPtrEqual>
+      mark2splits_;
+  /*!
+   * \brief Collect all mark2splits recursively from indices.
+   * \param indices The iterator of interest.
+   */
+  void Collect(const Array<IterSumExpr>& indices) {
+    for (IterSumExpr sum_expr : indices) {
+      for (IterSplitExpr split : sum_expr->args) {
+        this->CollectInternal(split->source);
+        mark2splits_[split->source].push_back(split);
+      }
+    }
+  }
+
+  void CollectInternal(const IterMark& mark) {
+    if (visited_.count(mark)) return;
+    visited_.insert(mark);
+    if (auto* op = mark->source.as<IterSumExprNode>()) {
+      for (IterSplitExpr split : op->args) {
+        this->CollectInternal(split->source);
+        mark2splits_[split->source].push_back(split);
+      }
+    }
+  }
+};
+
+// Rewriter to rewrite oinformations in iter
+class IterMapRewriter : public ExprMutator {
+ public:
+  using Parent = ExprMutator;
+
+  explicit IterMapRewriter(Analyzer* analyzer, const Map<Var, Range>& input_iters)
+      : analyzer_(analyzer) {
+    for (auto kv : input_iters) {
+      const auto& vrng = kv.second;
+      if (is_zero(vrng->min)) {
+        IterMark mark(kv.first, vrng->extent);
+        var_map_[kv.first] = IterSplitExpr(mark);
+        input_marks_.push_back(mark);
+      } else {
+        IterMark mark(kv.first - vrng->min, vrng->extent);
+        auto sum_expr = ToIterSumExpr(IterSplitExpr(mark));
+        sum_expr.CopyOnWrite()->base = vrng->min;
+        var_map_[kv.first] = sum_expr;
+        input_marks_.push_back(mark);
+      }
+    }
+  }
+
+  size_t unresolved_count() const { return unresolved_count_; }
+
+  IterSumExpr Rewrite(PrimExpr expr) {
+    return NormalizeToIterWithOffset(ToIterSumExpr(DirectMutate(expr)));
+  }
+
+  bool CheckBijective(const Array<IterSumExpr>& indices) {
+    IterMarkSplitCollector collector;
+    // We can check that for each iter mark:
+    // All the splits that refers to the itermark covers its extent.
+    // The splits do not overlap with each other.
+    collector.Collect(indices);
+    for (IterMark mark : collector.visited_) {
+      if (TryNormalizeSplits(mark, collector.mark2splits_[mark]).size() == 0) return false;
+    }
+    // all input marks must be visited
+    for (auto mark : input_marks_) {
+      if (collector.visited_.count(mark) == 0) return false;
+    }
+    return true;
+  }
+
+  // override the original mutate function.
+  PrimExpr VisitExpr(const PrimExpr& input_expr) final {
+    auto expr = ExprMutator::VisitExpr(input_expr);
+    if (expr->IsInstance<IterMapExprNode>()) {
+      ++unresolved_count_;
+    }
+    return expr;
+  }
+
+  // Normal mutation without normalization.
+  PrimExpr DirectMutate(PrimExpr expr) { return ExprMutator::VisitExpr(expr); }
+
+  PrimExpr VisitExpr_(const VarNode* op) final;
+  PrimExpr VisitExpr_(const AddNode* op) final;
+  PrimExpr VisitExpr_(const SubNode* op) final;
+  PrimExpr VisitExpr_(const MulNode* op) final;
+  PrimExpr VisitExpr_(const FloorDivNode* op) final;
+  PrimExpr VisitExpr_(const FloorModNode* op) final;
+
+ private:
+  // temp hash for de-duplication purposes.
+  struct IterSumHash {
+    size_t operator()(const IterSumExpr& value) const {
+      // for now only hash on source index.
+      size_t hash = value->args.size();
+      for (size_t i = 0; i < value->args.size(); ++i) {
+        hash = support::HashCombine(hash, std::hash<const Object*>()(value->args[i]->source.get()));
+      }
+      return hash;
+    }
+  };
+
+  struct IterSumEqual {
+    bool operator()(const IterSumExpr& lhs, const IterSumExpr& rhs) const {
+      tir::ExprDeepEqual equal;
+      if (lhs->args.size() != rhs->args.size()) return false;
+      if (!equal(lhs->base, rhs->base)) return false;
+      for (size_t i = 0; i < lhs->args.size(); ++i) {
+        auto lvalue = lhs->args[i];
+        auto rvalue = lhs->args[i];
+        if (!lvalue->source.same_as(rvalue->source)) return false;
+        if (!equal(lvalue->lower_factor, rvalue->lower_factor)) return false;
+        if (!equal(lvalue->scale, rvalue->scale)) return false;
+        if (!equal(lvalue->extent, rvalue->extent)) return false;
+      }
+      return true;
+    }
+  };
+
+  // Internal analyzer
+  Analyzer* analyzer_;
+  // Counter to keep track of unresolved cases.
+  int unresolved_count_{0};
+  // The var map
+  std::unordered_map<Var, PrimExpr, ObjectPtrHash, ObjectPtrEqual> var_map_;
+  // input iter marks
+  std::vector<IterMark> input_marks_;
+  // The canonical map for sum
+  std::unordered_map<IterSumExpr, IterSplitExpr, IterSumHash, IterSumEqual> sum_fuse_map_;
+
+  /*!
+   * \brief Verify that splits fully covers mark in a non-overlapping fashion.
+   *        If verification passes, return splits from outermost to inner most order.
+   *        If not, return an empty array
+   * \param mark The iterator of interest.
+   * \param splits The splits to be verified.
+   * \return The normalized splits.
+   */
+  Array<IterSplitExpr> TryNormalizeSplits(const IterMark& mark,
+                                          const std::vector<IterSplitExpr>& splits)
{
+    std::vector<bool> used(splits.size(), false);
+    std::vector<IterSplitExpr> iters;
+    PrimExpr expected_lower_factor = make_const(mark->source->dtype, 1);
+
+    for (size_t i = 0; i < splits.size(); ++i) {
+      size_t j = 0;
+      for (; j < splits.size(); ++j) {
+        if (used[j]) continue;
+        if (!used[j] && CanProveEqual(splits[j]->lower_factor, expected_lower_factor))
break;
+      }
+      if (j == splits.size()) {
+        return Array<IterSplitExpr>();
+      }
+      used[j] = true;
+      iters.push_back(splits[j]);
+      expected_lower_factor *= splits[j]->extent;
+    }
+    if (!CanProveEqual(expected_lower_factor, mark->extent)) return Array<IterSplitExpr>();
+    return Array<IterSplitExpr>(iters.rbegin(), iters.rend());
+  }
+
+  /*!
+   * \brief Normalize expr to an iterator + offset.
+   * \param expr The input expression.
+   * \return The Normalized expression.
+   */
+  IterSumExpr NormalizeToIterWithOffset(IterSumExpr expr) {
+    if (expr->args.size() <= 1) return expr;
+    PrimExpr base = expr->base;
+    expr.CopyOnWrite()->base = make_zero(expr->dtype);
+    auto opt = TryFuseIters(expr);
+    expr.CopyOnWrite()->base = base;
+    if (opt) {
+      expr.CopyOnWrite()->args = Array<IterSplitExpr>({opt.value()});
+      return expr;
+    } else {
+      ++unresolved_count_;
+      return expr;
+    }
+  }
+
+  bool CanProveEqual(PrimExpr lhs, PrimExpr rhs) {
+    const auto* clhs = lhs.as<IntImmNode>();
+    const auto* crhs = rhs.as<IntImmNode>();
+    if (clhs && crhs) return clhs->value == crhs->value;
+    return analyzer_->CanProve(lhs - rhs == 0);
+  }
+
+  /*!
+   * \brief Create a IterSumExpr from expr.
+   * \param expr The input expr.
+   * \return The transformed IterSumExpr.
+   */
+  IterSumExpr ToIterSumExpr(PrimExpr expr) {
+    if (const auto* op = expr.as<IterSumExprNode>()) {
+      return GetRef<IterSumExpr>(op);
+    } else if (const auto* op = expr.as<IterSplitExprNode>()) {
+      return IterSumExpr({GetRef<IterSplitExpr>(op)}, make_zero(expr->dtype));
+    } else {
+      CHECK(!expr->IsInstance<IterMapExprNode>());
+      return IterSumExpr({}, expr);
+    }
+  }
+
+  // Try to normalize IterSum into a fused IterMark
+  // return a corresponding splitexpr if needed.
+  Optional<IterSplitExpr> TryFuseIters(IterSumExpr expr) {
+    if (!is_zero(expr->base)) return NullOpt;
+    if (expr->args.size() == 1) return expr->args[0];
+    // select the iterators in order
+    std::vector<bool> visited(expr->args.size(), false);
+    std::vector<IterSplitExpr> iters;
+    iters.reserve(expr->args.size());
+    // canonicalize the expression
+    // check if it can be remapped into a fused pattern.
+    PrimExpr expected_scale = make_const(expr->base->dtype, 1);
+    for (size_t i = 0; i < expr->args.size(); ++i) {
+      size_t j = 0;
+      for (; j < expr->args.size(); ++j) {
+        if (!visited[j] && CanProveEqual(expr->args[j]->scale, expected_scale))
break;
+      }
+      if (j == expr->args.size()) {
+        return NullOpt;
+      }
+      visited[j] = true;
+      iters.push_back(expr->args[j]);
+      expected_scale *= expr->args[j]->extent;
+    }
+    // update the iterator to use the canonicalized form
+    expr.CopyOnWrite()->args = Array<IterSplitExpr>(iters.rbegin(), iters.rend());
+    auto it = sum_fuse_map_.find(expr);
+    if (it != sum_fuse_map_.end()) return it->second;
+    auto mark = IterMark(expr, expected_scale);
+    IterSplitExpr split(mark);
+    sum_fuse_map_[expr] = split;
+    return split;
+  }
+
+  bool CanProveDivisible(PrimExpr lhs, PrimExpr rhs) {
+    const auto* clhs = lhs.as<IntImmNode>();
+    const auto* crhs = rhs.as<IntImmNode>();
+    if (clhs && crhs) return clhs->value % crhs->value == 0;
+    return analyzer_->CanProve(floormod(lhs, rhs) == 0);
+  }
+
+  PrimExpr SplitFloorDivConst(IterSplitExpr lhs, PrimExpr rhs);
+  PrimExpr SplitFloorModConst(IterSplitExpr lhs, PrimExpr rhs);
+
+  static void AddToLhs(IterSumExprNode* lhs, IterSplitExpr rhs, int sign) {
+    tir::ExprDeepEqual equal;
+    for (size_t i = 0; i < lhs->args.size(); ++i) {
+      IterSplitExpr lvalue = lhs->args[i];
+      if (lvalue->source.same_as(rhs->source) && equal(lvalue->lower_factor,
rhs->lower_factor) &&
+          equal(lvalue->extent, rhs->extent)) {
+        if (sign > 0) {
+          rhs.CopyOnWrite()->scale = lvalue->scale + rhs->scale;
+        } else {
+          rhs.CopyOnWrite()->scale = lvalue->scale - rhs->scale;
+        }
+        lhs->args.Set(i, rhs);
+        return;
+      }
+    }
+    if (sign > 0) {
+      lhs->args.push_back(rhs);
+    } else {
+      rhs.CopyOnWrite()->scale = make_zero(rhs->scale.dtype()) - rhs->scale;
+      lhs->args.push_back(rhs);
+    }
+  }
+
+  static void AddToLhs(IterSumExprNode* lhs, IterSumExpr rhs, int sign) {
+    for (size_t i = 0; i < rhs->args.size(); ++i) {
+      AddToLhs(lhs, rhs->args[i], sign);
+    }
+    if (sign > 0) {
+      lhs->base += rhs->base;
+    } else {
+      lhs->base -= rhs->base;
+    }
+  }
+
+  static void MulToLhs(IterSumExprNode* lhs, PrimExpr rhs) {
+    for (size_t i = 0; i < lhs->args.size(); ++i) {
+      IterSplitExpr lvalue = lhs->args[i];
+      lvalue.CopyOnWrite()->scale *= rhs;
+      lhs->args.Set(i, lvalue);
+    }
+    lhs->base *= rhs;
+  }
+};
+
+Array<IterSumExpr> DetectIterMap(const Array<PrimExpr>& indices, const Map<Var,
Range>& input_iters,
+                                 arith::Analyzer* analyzer) {
+  // Overall detection algorithm is divided into two steps:
+  // - Step0: IterMapRewriter rewrites the expression to use IterMapExpr patterns.
+  // - Step1: IterIndependenceChecker checks if the iterator are independent.
+  IterMapRewriter rewriter(analyzer, input_iters);
+  Array<IterSumExpr> results;
+
+  for (PrimExpr value : indices) {
+    results.push_back(rewriter.Rewrite(value));
+    if (rewriter.unresolved_count() != 0) return Array<IterSumExpr>();
+  }
+  if (!rewriter.CheckBijective(results)) return Array<IterSumExpr>();

Review comment:
       The checks are via the TryNormalizeSplits function




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