[ARITH] RewriteSimplifier: add/sub/mul/div/mod

include/tvm/arithmetic.h

@@ -192,6 +192,39 @@ class ModularSetAnalyzer {
   Impl* impl_;
 };
 
+/*!
+ * \brief Rewrite-rule based simplifier.
+ */
+class RewriteSimplifier {
+ public:
+  /*!
+   * \brief analyze the expr
+   * \param expr The expression of interest.
+   * \return the result of the analysis.
+   */
+  Expr operator()(const Expr& expr);
+
+  /*!
+   * \brief Update binding of var to a new expression.
+   *
+   * \param var The variable of interest.
+   * \param new_expr
+   * \param override Whether do we allow override of existing information.
+   */
+  void Update(const Var& var,
+              const Expr& new_expr,
+              bool override = false);
+
+ private:
+  friend class Analyzer;
+  friend class ConstraintContext;
+  explicit RewriteSimplifier(Analyzer* parent);
+  ~RewriteSimplifier();
+  class Impl;
+  /*! \brief Internal impl */
+  Impl* impl_;
+};
+
 /*!
  * \brief A RAII constraint context.
  *
@@ -242,6 +275,8 @@ class Analyzer {
   ConstIntBoundAnalyzer const_int_bound;
   /*! \brief sub-analyzer: modular set */
   ModularSetAnalyzer modular_set;
+  /*! \brief sub-analyzer rewrite simplfy */
+  RewriteSimplifier rewrite_simplify;
   /*! \brief constructor */
   Analyzer();
   /*!

python/tvm/arith.py

@@ -96,6 +96,7 @@ def __init__(self):
         self._const_int_bound_update = _mod("const_int_bound_update")
         self._bind = _mod("bind")
         self._modular_set = _mod("modular_set")
+        self._rewrite_simplify = _mod("rewrite_simplify")
         self._enter_constraint_context = _mod("enter_constraint_context")
 
     def const_int_bound(self, expr):
@@ -128,6 +129,21 @@ def modular_set(self, expr):
         """
         return self._modular_set(expr)
 
+    def rewrite_simplify(self, expr):
+        """Simplify expression via rewriting rules.
+
+        Parameters
+        ----------
+        expr : tvm.Expr
+            The expression.
+
+        Returns
+        -------
+        result : Expr
+            The result.
+        """
+        return self._rewrite_simplify(expr)
+
     def bind(self, var, expr):
         """Bind a variable to the expression.
 

src/api/api_arith.cc

@@ -98,6 +98,10 @@ TVM_REGISTER_API("arith._CreateAnalyzer")
         return PackedFunc([self](TVMArgs args, TVMRetValue *ret) {
             self->const_int_bound.Update(args[0], args[1], args[2]);
         });
+      } else if (name == "rewrite_simplify") {
+        return PackedFunc([self](TVMArgs args, TVMRetValue *ret) {
+            *ret = self->rewrite_simplify(args[0]);
+        });
       } else if (name == "bind") {
         return PackedFunc([self](TVMArgs args, TVMRetValue *ret) {
             auto& sptr = args[1].node_sptr();

src/arithmetic/analyzer.cc

@@ -2,26 +2,30 @@
  *  Copyright (c) 2019 by Contributors
  * \file tvm/arithmetic/analyzer.cc
  */
+#include <tvm/ir.h>
 #include <tvm/arithmetic.h>
 
 namespace tvm {
 namespace arith {
 
 Analyzer::Analyzer()
     : const_int_bound(this),
-      modular_set(this) {
+      modular_set(this),
+      rewrite_simplify(this) {
 }
 
 void Analyzer::Bind(const VarExpr& v, const Expr& expr) {
   Var var(v.node_);
   this->const_int_bound.Update(var, this->const_int_bound(expr));
   this->modular_set.Update(var, this->modular_set(expr));
+  this->rewrite_simplify.Update(var, this->rewrite_simplify(expr));
 }
 
 void Analyzer::Bind(const VarExpr& v, const Range& range) {
   Var var(v.node_);
   this->const_int_bound.Bind(var, range);
   // skip modular_set
+  // skip rewrite simplify
 }
 
 ConstraintContext::ConstraintContext(Analyzer* analyzer, const Expr& constraint) {
@@ -36,7 +40,10 @@ ConstraintContext::ConstraintContext(Analyzer* analyzer, const Expr& constraint)
 }
 
 bool Analyzer::CanProveGreaterEqual(const Expr& expr, int64_t lower_bound) {
-  auto bd = this->const_int_bound(expr);
+  if (const auto* ptr = expr.as<ir::IntImm>()) {
+    return ptr->value > lower_bound;
+  }
+  auto bd = this->const_int_bound(this->rewrite_simplify(expr));
   if (bd->min_value >= lower_bound) return true;
   return false;
 }

src/arithmetic/const_fold.h

@@ -23,7 +23,9 @@ namespace arith {
  * \return nullptr if constant fold fails, otherwise return folded result.
  */
 template<typename Op>
-inline Expr TryConstFold(Expr a, Expr b);
+inline Expr TryConstFold(Expr a, Expr b) {
+  return Expr();
+}
 
 /*!
  * \brief Try to run unary compute with constant folding.

src/arithmetic/pattern_match.h

@@ -49,6 +49,7 @@
 
 #include <tvm/ir_pass.h>
 #include <tuple>
+#include "const_fold.h"
 
 namespace tvm {
 namespace arith {
@@ -242,20 +243,60 @@ class PBinaryExpr :
   }
 
   Expr Eval() const {
-    return NodeType::make(a_.Eval(), b_.Eval());
+    Expr lhs = a_.Eval();
+    Expr rhs = b_.Eval();
+    Expr ret = TryConstFold<NodeType>(lhs, rhs);
+    if (ret.defined()) return ret;
+    return NodeType::make(lhs, rhs);
   }
 
  private:
   typename TA::Nested a_;
   typename TB::Nested b_;
 };
 
+template<typename TA>
+class PConstWithTypeLike :
+      public Pattern<PConstWithTypeLike<TA> > {
+ public:
+  PConstWithTypeLike(const TA& ref, int64_t value)
+      : ref_(ref), value_(value) {}
+
+  void InitMatch_() const {}
+
+  bool Match_(const NodeRef& node) const {
+    if (const ir::IntImm* ptr = node.as<ir::IntImm>()) {
+      return ptr->value == value_;
+    } else {
+      return false;
+    }
+  }
+
+  Expr Eval() const {
+    return make_const(ref_.Eval().type(), value_);
+  }
+
+ private:
+  typename TA::Nested ref_;
+  int64_t value_;
+};
+
 
-#define TVM_PATTERN_BINARY_OP(FuncName, NodeName)             \
-  template<typename TA, typename TB>                          \
-  inline PBinaryExpr<NodeName, TA, TB>                        \
-  FuncName(const Pattern<TA>& a, const Pattern<TB>& b) {      \
+#define TVM_PATTERN_BINARY_OP(FuncName, NodeName)                   \
+  template<typename TA, typename TB>                                \
+  inline PBinaryExpr<NodeName, TA, TB>                              \
+  FuncName(const Pattern<TA>& a, const Pattern<TB>& b) {            \
     return PBinaryExpr<NodeName, TA, TB>(a.derived(), b.derived()); \
+  }                                                                 \
+  template<typename TA>                                             \
+  inline PBinaryExpr<NodeName, TA, PConstWithTypeLike<TA> >         \
+  FuncName(const Pattern<TA>& a, int64_t b) {                       \
+    return FuncName(a, PConstWithTypeLike<TA>(a.derived(), b));     \
+  }                                                                 \
+  template<typename TA>                                             \
+  inline PBinaryExpr<NodeName, PConstWithTypeLike<TA>, TA>          \
+  FuncName(int64_t b, const Pattern<TA>& a) {                       \
+    return FuncName(PConstWithTypeLike<TA>(a.derived(), b), a);     \
   }
 
 // arithmetic expressions