[GitHub] [tvm] tqchen commented on a change in pull request #7045: [Arith] Simplify cast

[GitBox <gi...@apache.org>]

tqchen commented on a change in pull request #7045:
URL: https://github.com/apache/tvm/pull/7045#discussion_r550500956



##########
File path: src/arith/canonical_simplify.cc
##########
@@ -77,6 +77,25 @@ inline PrimExpr DivImpl(PrimExpr a, PrimExpr b, DivMode mode) {
   }
 }
 
+bool CheckCastImpl(DataType dtype, PrimExpr value, Analyzer* analyzer) {

Review comment:
       Perhaps rename to UpcastIsSafe?

##########
File path: src/arith/canonical_simplify.cc
##########
@@ -128,6 +147,50 @@ class SplitExprNode : public CanonicalExprNode {
 
   void MulToSelf(int64_t scale) { this->scale *= scale; }
 
+  /*!
+   * \brief check if cast(dtype, self) is safe
+   * \param dtype The target datatype
+   * \param analyzer The analyzer
+   * \return whether the cast is safe or not
+   */
+  bool CheckCast(DataType dtype, Analyzer* analyzer) const {

Review comment:
       CanPushCastToChildren

##########
File path: src/arith/canonical_simplify.cc
##########
@@ -77,6 +77,25 @@ inline PrimExpr DivImpl(PrimExpr a, PrimExpr b, DivMode mode) {
   }
 }
 
+bool CheckCastImpl(DataType dtype, PrimExpr value, Analyzer* analyzer) {
+  if (!IsIndexType(dtype)) {
+    return false;
+  }
+  ConstIntBound bound = analyzer->const_int_bound(value);
+  int64_t ubound = Downcast<IntImm>(max_value(dtype))->value;
+  int64_t lbound = Downcast<IntImm>(min_value(dtype))->value;
+  if (value.dtype().bits() <= dtype.bits() ||  // upcast is safe
+      (bound->max_value <= ubound && bound->min_value >= lbound)) {
+    return true;
+  }
+  return false;
+}
+
+#define TVM_CHECK_CANONICAL_SIMPLIFY_CAST(DTYPE, VALUE) \
+  if (!CheckCastImpl(DTYPE, VALUE, analyzer)) {         \

Review comment:
       inline the function call, while macro makes the code a bit more concise, it makes the code itself harder to understand.

##########
File path: src/arith/canonical_simplify.cc
##########
@@ -77,6 +77,25 @@ inline PrimExpr DivImpl(PrimExpr a, PrimExpr b, DivMode mode) {
   }
 }
 
+bool CheckCastImpl(DataType dtype, PrimExpr value, Analyzer* analyzer) {

Review comment:
       document this function

##########
File path: src/arith/canonical_simplify.cc
##########
@@ -255,6 +318,61 @@ class SumExprNode : public CanonicalExprNode {
 
   void AddToSelf(const SumExpr& other, int64_t scale);
 
+  /*!
+   * \brief check if cast(dtype, self) is safe
+   * \param dtype The target datatype
+   * \param analyzer The analyzer
+   * \return whether the cast is safe or not
+   */
+  bool CheckCast(DataType dtype, Analyzer* analyzer) const {
+    // cast(dtype, arg_1 + arg_2 + ... arg_n) ==
+    // cast(dtype, arg_1) + ... + cast(dtype, arg_n)
+    // iff it is an upcast (dtype.bits >= self.dtype.bits) or all of
+    // its intermediate results fit in the range of dtype
+    if (dtype.bits() >= this->dtype.bits()) {
+      return true;  // upcast is safe
+    }
+    PrimExpr res = make_const(dtype, 0);
+    for (size_t i = 0; i < args.size(); ++i) {
+      if (args[i]->scale > 0) {
+        res = res + args[i]->Normalize();
+        TVM_CHECK_CANONICAL_SIMPLIFY_CAST(dtype, res)
+      }
+    }
+    if (base > 0) {
+      res = res + make_const(dtype, base);
+      TVM_CHECK_CANONICAL_SIMPLIFY_CAST(dtype, res)
+    }
+    // negative scales follows using sub.
+    for (size_t i = 0; i < args.size(); ++i) {
+      if (args[i]->scale < 0) {
+        res = res - args[i]->NormalizeWithScale(-1);
+        TVM_CHECK_CANONICAL_SIMPLIFY_CAST(dtype, res)
+      }
+    }
+    if (base < 0) {
+      res = res - make_const(dtype, -base);
+      TVM_CHECK_CANONICAL_SIMPLIFY_CAST(dtype, res)
+    }
+    for (const auto& arg : args) {
+      if (!arg->CheckCast(dtype, analyzer)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /*!
+   * \brief self = cast(dtype, self)
+   * \param dtype The target datatype
+   */
+  void CastTo(DataType dtype) {

Review comment:
       PushCastToChildren

##########
File path: src/arith/canonical_simplify.cc
##########
@@ -128,6 +147,50 @@ class SplitExprNode : public CanonicalExprNode {
 
   void MulToSelf(int64_t scale) { this->scale *= scale; }
 
+  /*!
+   * \brief check if cast(dtype, self) is safe
+   * \param dtype The target datatype
+   * \param analyzer The analyzer
+   * \return whether the cast is safe or not
+   */
+  bool CheckCast(DataType dtype, Analyzer* analyzer) const {
+    // cast(dtype, index % upper_factor / lower_factor * scale) ==
+    // cast(dtype, index) % upper_factor / lower_factor * scale
+    // iff it is an upcast (dtype.bits >= self.dtype.bits) or all of
+    // its intermediate results fit in the range of dtype
+    if (dtype.bits() >= this->dtype.bits()) {
+      return true;  // upcast is safe
+    }
+    PrimExpr res = this->index;
+    if (this->scale == 0) {
+      return true;
+    }
+    TVM_CHECK_CANONICAL_SIMPLIFY_CAST(dtype, res)
+    if (this->upper_factor != SplitExprNode::kPosInf) {
+      res = ModImpl(res, make_const(this->dtype, this->upper_factor), div_mode);
+      TVM_CHECK_CANONICAL_SIMPLIFY_CAST(dtype, res)
+    }
+    if (this->lower_factor != 1) {
+      res = DivImpl(res, make_const(this->dtype, this->lower_factor), div_mode);
+      TVM_CHECK_CANONICAL_SIMPLIFY_CAST(dtype, res)
+    }
+    if (this->scale != 1) {
+      ICHECK(!this->dtype.is_uint() || this->scale > 0);
+      res = res * make_const(this->dtype, this->scale);
+      TVM_CHECK_CANONICAL_SIMPLIFY_CAST(dtype, res)
+    }
+    return true;
+  }
+
+  /*!
+   * \brief self = cast(dtype, self)
+   * \param dtype The target datatype
+   */
+  void CastTo(DataType dtype) {

Review comment:
       Rename to `PushCastToChildren`

##########
File path: src/arith/canonical_simplify.cc
##########
@@ -1071,6 +1192,32 @@ PrimExpr CanonicalSimplifier::Impl::VisitExpr_(const ReduceNode* op) {
   return ret;
 }
 
+PrimExpr CanonicalSimplifier::Impl::VisitExpr_(const CastNode* op) {
+  if (!IsIndexType(op->dtype)) {
+    return Rewriter::VisitExpr_(op);
+  }
+  // normalize
+  PrimExpr value = this->CanonicalMutate(op->value);
+  PrimExpr ret;

Review comment:
       comment: PushCastToChildren




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