[LANG] Introduce Scan, bugfix Canonical

Author: tqchen

include/tvm/ir.h

@@ -49,12 +49,27 @@ struct Reduce : public ExprNode<Reduce> {
   static constexpr const char* Min = "Min";
 };
 
-/*! \brief namespace of possible attribute sin AttrStmt.type_key */
-namespace attr {
 /*!
- * \brief Mark scope of iteration variable, used by Schedule.
+ * \brief Auxiliary data structure used in IR Pass to indicate a tensor.
  */
-constexpr const char* scope = "scope";
+struct TensorKey {
+  FunctionRef f;
+  int value_index;
+
+  inline bool operator==(const TensorKey& other) const {
+    return f == other.f && value_index == other.value_index;
+  }
+  inline std::string GetName() const {
+    if (f->num_outputs() == 1) return f->func_name();
+    std::ostringstream os;
+    os << f->func_name() << ".v" << value_index;
+    return os.str();
+  }
+};
+
+/*! \brief namespace of possible attribute sin AttrStmt.type_key */
+namespace attr {
+// The above attr does not pass to ir stage.
 /*!
  * \brief Mark launching extent of thread, used by device API.
  */
@@ -189,4 +204,16 @@ using Halide::Internal::Evaluate;
 }  // namespace ir
 }  // namespace tvm
 
+namespace std {
+template <>
+struct hash<::tvm::ir::TensorKey> {
+  std::size_t operator()(const ::tvm::ir::TensorKey& k) const {
+    size_t lhs = k.f.hash();
+    size_t rhs = static_cast<size_t>(k.value_index);
+    lhs ^= rhs + 0x9e3779b9 + (lhs << 6) + (lhs >> 2);
+    return lhs;
+  }
+};
+}  // namespace std
+
 #endif  // TVM_IR_H_

include/tvm/operation.h

@@ -77,6 +77,55 @@ class ComputeOpNode : public OperationNode {
   TVM_DECLARE_NODE_TYPE_INFO(ComputeOpNode);
 };
 
+/*!
+ * \brief Symbolic scan.
+ */
+class ScanOpNode : public OperationNode {
+ public:
+  /*! \brief IterVar to scan over */
+  IterVar scan_axis;
+  /*! \brief the initialization tensors */
+  Array<Tensor> init;
+  /*! \brief the update function represented by tensor */
+  Array<Tensor> update;
+  /*! \brief The placeholder to refer as states in update. */
+  Array<Tensor> state_placeholder;
+  /*!
+   * \brief Spatial axis to indicate spatial dimension of each output.
+   *  They corresponds to flattened spatial axis of the outputs.
+   *
+   *  [output[0].axis[1], output[0].axis[2]... output[k].axis[j]...]
+   *  These are auxiliary data structure for storing result of bound inference.
+   *  They do not corresponds to splittable iterations, thus the name comes
+   *  with underscore.
+   */
+  Array<IterVar> spatial_axis_;
+  /*! \brief constructor */
+  ScanOpNode() {}
+  // override behavior.
+  int num_outputs() const final;
+  Array<IterVar> root_iter_vars() const final;
+  Type output_dtype(size_t i) const final;
+  Array<Expr> output_shape(size_t i) const final;
+
+  void VisitAttrs(AttrVisitor* v) final {
+    v->Visit("name", &name);
+    v->Visit("scan_axis", &scan_axis);
+    v->Visit("init", &init);
+    v->Visit("update", &update);
+    v->Visit("state_placeholder", &state_placeholder);
+    v->Visit("spatial_axis_", &spatial_axis_);
+  }
+  static Operation make(std::string name,
+                        IterVar axis,
+                        Array<Tensor> init,
+                        Array<Tensor> update,
+                        Array<Tensor> state_placeholder);
+
+  static constexpr const char* _type_key = "ScanOp";
+  TVM_DECLARE_NODE_TYPE_INFO(ScanOpNode);
+};
+
 
 /*! \brief The compute function to specify the input source of a Tensor */
 using FCompute = std::function<Expr (const Array<Var>& i)>;
@@ -100,6 +149,21 @@ Tensor Placeholder(Array<Expr> shape,
  */
 Tensor Compute(Array<Expr> shape, FCompute fcompute, std::string name = "tensor");
 
+/*!
+ * \brief Construct new tensors by scan over scan_axis.
+ *
+ * \param scan_axis The iteration representing the scan.
+ * \param init The intialize tensor of first K steps.
+ * \param update The update tensor indicated the updated result after each timestamp.
+ * \param state_placeholder The placeholder for the states.
+ * \param name The optional name of the tensor.
+ */
+Array<Tensor> Scan(IterVar scan_axis,
+                   Array<Tensor> init,
+                   Array<Tensor> update,
+                   Array<Tensor> state_placeholder,
+                   std::string name = "scan");
+
 // same as compute, specialized for different fcompute function
 inline Tensor Compute(Array<Expr> shape,
                       std::function<Expr(Var)> f,

python/tvm/api.py

@@ -14,6 +14,7 @@
 from . import _api_internal
 from . import make as _make
 from . import expr as _expr
+from . import tensor as _tensor
 from . import collections as _collections
 
 int32 = "int32"
@@ -111,7 +112,6 @@ def compute(shape, fcompute, name="compute"):
     shape: Tuple of Expr
         The shape of the tensor
 
-
     fcompute: lambda function of *indices-> value
         Specifies the input source expression
 
@@ -137,8 +137,59 @@ def compute(shape, fcompute, name="compute"):
     body = convert(body)
     op_node = _api_internal._ComputeOp(
         name, dim_var, body)
-    return _api_internal._Tensor(
-        shape, body.dtype, op_node, 0)
+    return op_node.output(0)
+
+
+def scan(axis, init, update, state_placeholder, name="scan"):
+    """Construct new tensors by scanning over axis.
+
+    Parameters
+    ----------
+    axis: IterVar
+        The scanning axis.
+
+    init: Tensor or list of Tensor
+        The initial condition of first init.shape[0] timestamps
+
+    update: Tensor or list of Tensor
+        The update rule of the scan given by symbolic tensor.
+
+    state_placeholder: Tensor or list of Tensor
+        The placeholder variables used by update.
+
+    name: str, optional
+        The name hint of the tensor
+
+    Returns
+    -------
+    tensor: tensor.Tensor
+        The created tensor
+
+    Example
+    -------
+    # take sum over rows of x
+    m = tvm.Var("m")
+    n = tvm.Var("n")
+    t = tvm.IterVar((1, m), "t")
+    x = tvm.placeholder((m, n))
+    s = tvm.placeholder((m, n))
+    res = tvm.scan(t,
+                   tvm.compute((1, n), lambda t, i: x[i]),
+                   tvm.compute((n,), lambda i: s[t-1] + x[i]),
+                   s)
+    # res[l-1] stores of sum of all rows in x
+    """
+    if isinstance(init, _tensor.Tensor):
+        init = [init]
+    if isinstance(update, _tensor.Tensor):
+        update = [update]
+    if isinstance(state_placeholder, _tensor.Tensor):
+        state_placeholder = [state_placeholder]
+    if len(init) != len(update) or len(init) != len(state_placeholder):
+        raise ValueError("init, update, state_placeholder must have same length")
+    op = _api_internal._ScanOp(name, axis, init, update, state_placeholder)
+    res = [op.output(i) for i in range(len(update))]
+    return (res[0] if len(res) == 1 else res)
 
 
 def Buffer(shape, dtype=None,

python/tvm/tensor.py

@@ -74,12 +74,17 @@ def output(self, index):
         """
         return _api_internal._OpGetOutput(self, index)
 
+@register_node
+class PlaceholderOp(Operation):
+    """Placeholder operation."""
+    pass
+
 @register_node
 class ComputeOp(Operation):
     """Compute operation."""
     pass
 
 @register_node
-class PlaceholderOp(Operation):
-    """Placeholder operation."""
+class ScanOp(Operation):
+    """Scan operation."""
     pass

src/api/api_lang.cc

@@ -173,6 +173,15 @@ TVM_REGISTER_API(_ComputeOp)
                                args[2]);
   });
 
+TVM_REGISTER_API(_ScanOp)
+.set_body([](TVMArgs args,  TVMRetValue* ret) {
+    *ret = ScanOpNode::make(args[0],
+                            args[1],
+                            args[2],
+                            args[3],
+                            args[4]);
+  });
+
 TVM_REGISTER_API(_OpGetOutput)
 .set_body([](TVMArgs args,  TVMRetValue* ret) {
     *ret = args[0].operator Operation().output(

src/arithmetic/canonical.cc

@@ -365,7 +365,7 @@ class Canonical::Internal : public IRMutator {
                   const ComExpr& sumb,
                   int bscale) {
     std::shared_ptr<ComExprNode> n = std::make_shared<ComExprNode>();
-    n->base = suma->base + sumb->base;
+    n->base = suma->base + sumb->base * bscale;
     // merge of suma and sumb;
     size_t i = 0, j = 0;
     while (i < suma->elem.size() && j < sumb->elem.size()) {
@@ -417,7 +417,7 @@ class Canonical::Internal : public IRMutator {
   // convert sum to expr
   Expr Sum2Expr(const ComExpr& com, Type t) {
     Expr vsum;
-    if (com->base != 0) {
+    if (com->base > 0) {
       vsum = make_const(t, com->base);
     }
     for (const ComExprEntry& e : com->elem) {
@@ -433,6 +433,13 @@ class Canonical::Internal : public IRMutator {
         }
       }
     }
+    if (com->base < 0) {
+      if (vsum.defined()) {
+        vsum = Sub::make(vsum, make_const(t, -com->base));
+      } else {
+        vsum = make_const(t, com->base);
+      }
+    }
     for (const ComExprEntry& e : com->elem) {
       if (e.scale < 0) {
         Expr v = e.value;

src/codegen/codegen_cuda.cc

@@ -168,7 +168,7 @@ MakeNVRTC(Array<LoweredFunc> funcs) {
     const auto& f = PackedFunc::GetGlobal("tvm_callback_cuda_postproc");
     code = f(code).operator std::string();
   }
-    LOG(INFO) << code;
+
   std::string ptx;
   if (PackedFunc::GlobalExist("tvm_callback_cuda_compile")) {
     const auto& f = PackedFunc::GetGlobal("tvm_callback_cuda_compile");

src/lang/operation.cc

@@ -5,6 +5,7 @@
 #include <tvm/operation.h>
 #include <tvm/tensor.h>
 #include <tvm/ir.h>
+#include <tvm/ir_pass.h>
 #include <memory>
 
 namespace tvm {
@@ -120,4 +121,90 @@ TVM_STATIC_IR_FUNCTOR(IRPrinter, vtable)
 
 TVM_REGISTER_NODE_TYPE(ComputeOpNode);
 
+// Scan
+inline bool prove_equal(Expr lhs, Expr rhs) {
+  return is_zero(ir::Simplify(lhs - rhs));
+}
+
+int ScanOpNode::num_outputs() const {
+  return update.size();
+}
+Array<IterVar> ScanOpNode::root_iter_vars() const {
+  return Array<IterVar>{scan_axis};
+}
+
+Type ScanOpNode::output_dtype(size_t i) const {
+  return update[i]->dtype;
+}
+
+Array<Expr> ScanOpNode::output_shape(size_t i) const {
+  CHECK_LT(i, state_placeholder.size());
+  return state_placeholder[i]->shape;
+}
+
+Operation ScanOpNode::make(std::string name,
+                           IterVar axis,
+                           Array<Tensor> init,
+                           Array<Tensor> update,
+                           Array<Tensor> state_placeholder) {
+  auto n = std::make_shared<ScanOpNode>();
+  CHECK_EQ(init.size(), update.size());
+  CHECK_EQ(init.size(), state_placeholder.size());
+
+  for (size_t i = 0; i < init.size(); ++i) {
+    CHECK_EQ(init[i]->dtype, state_placeholder[i]->dtype);
+    CHECK_EQ(init[i]->dtype, update[i]->dtype);
+    CHECK(can_prove(init[i]->shape[0] == axis->dom->min))
+        << "init.shape[0] need to match scan_axis.dom.min";
+    CHECK(prove_equal(
+        state_placeholder[i]->shape[0], axis->dom->min + axis->dom->extent))
+        << "shate_placeholder.shape[0] need to match"
+        << " scan_axis.dom.min + scan_axis.dom.extent";
+    CHECK_EQ(state_placeholder[i].ndim(), init[i].ndim())
+        << "The dimension of init need to match state_placeholder";
+    CHECK_EQ(update[i].ndim() + 1, state_placeholder[i].ndim())
+        << "The update.ndim need to be state_placeholder.ndim - 1";
+    for (size_t k = 0;  k < update[i].ndim(); ++k) {
+      CHECK(prove_equal(
+          update[i]->shape[k], state_placeholder[i]->shape[k + 1]));
+      // setup spatial axis
+      std::ostringstream spatial_name;
+      spatial_name << name << ".out" << i << ".i" << k + 1;
+      n->spatial_axis_.push_back(
+          IterVar(Range::make_with_min_extent(0, update[i]->shape[k]),
+                  spatial_name.str()));
+    }
+    for (size_t k = 1;  k < init[i].ndim(); ++k) {
+      CHECK(prove_equal(
+          init[i]->shape[k], state_placeholder[i]->shape[k]));
+    }
+  }
+
+  n->name = name;
+  n->scan_axis = axis;
+  n->init = init;
+  n->update = update;
+  n->state_placeholder = state_placeholder;
+  return Operation(n);
+}
+
+Array<Tensor> Scan(IterVar scan_axis,
+                   Array<Tensor> init,
+                   Array<Tensor> update,
+                   Array<Tensor> state_placeholder,
+                   std::string name) {
+  Operation op = ScanOpNode::make(
+      name, scan_axis, init, update, state_placeholder);
+  Array<Tensor> res;
+  for (int i = 0; i < op->num_outputs(); ++i) {
+    res.push_back(op.output(i));
+  }
+  return res;
+}
+
+TVM_STATIC_IR_FUNCTOR(IRPrinter, vtable)
+.set_dispatch<ScanOpNode>([](const ScanOpNode *op, IRPrinter *p) {
+    p->stream << "scan(" << op->name << ", " << op << ")";
+});
+
 }  // namespace tvm