hanke580 commented on a change in pull request #6370:
URL: https://github.com/apache/tvm/pull/6370#discussion_r555209975



##########
File path: include/tvm/topi/einsum.h
##########
@@ -0,0 +1,930 @@
+/*
+ * 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 topi/einsum.h
+ * \brief Einstein summation op
+ */
+#ifndef TVM_TOPI_EINSUM_H_
+#define TVM_TOPI_EINSUM_H_
+
+#include <tvm/te/operation.h>
+#include <tvm/tir/data_layout.h>
+#include <tvm/topi/detail/constant_utils.h>
+#include <tvm/topi/detail/ravel_unravel.h>
+#include <tvm/topi/detail/tensor_utils.h>
+#include <tvm/topi/tags.h>
+
+#include <algorithm>
+#include <bitset>
+#include <iterator>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+namespace tvm {
+namespace topi {
+
+using namespace tvm::te;
+using namespace topi::detail;
+
+/*!
+ * \brief Compute the stride of the given shape.
+ *
+ * \param shape for the operation.
+ *
+ * \return the stride of the shape.
+ */
+inline Array<PrimExpr> GetStride(const Array<PrimExpr> shape) {
+  size_t ndim = shape.size();
+  int prod = 1;
+  Array<PrimExpr> stride = Array<PrimExpr>(ndim, -1);
+  for (int i = ndim - 1; i >= 0; i--) {
+    stride.Set(i, if_then_else(shape[i] > 1, prod, 0));
+    prod = prod * GetConstInt(shape[i]);
+  }
+  return stride;
+}
+
+/*!
+ * \brief Pad the shape with 1.
+ *
+ * \param shape the input shape to be padded
+ * \param odim the padding size of the objective shape.
+ *
+ * \return the padded shape.
+ */
+inline Array<PrimExpr> Pad(const Array<PrimExpr> shape, int odim) {
+  int ndim = shape.size();
+  CHECK_GE(odim, ndim);
+  Array<PrimExpr> ret(static_cast<size_t>(odim), 1);
+  for (int idim = 0; idim < ndim; ++idim) {
+    ret.Set(idim, shape[idim]);
+  }
+  return ret;
+}
+
+/*!
+ * \brief Parse the subscripts for one operand into an output of 'ndim' labels.
+ *
+ * \param subscripts the subscripts for to be parsed.
+ * \param length subscripts[0: length] represents the current operand.
+ * \param ndim the ndim of current operand.
+ * \param iop the index of the operand.
+ * \param op_labels the parsing result.
+ *        For Example:
+ *           subscripts="abbcbc",  ndim=6 -> op_labels=[97, 98, -1, 99, -3, 
-2].
+ *           subscripts="ab...bc", ndim=6 -> op_labels=[97, 98, 0, 0, -3, 99].
+ * \param label_counts Count the number the label appears.
+ * \param min_label Save the minimal label according to ASCII.
+ * \param max_label Save the maximal label according to ASCII.
+ *
+ * \return 0.
+ */
+inline int ParseOperandSubscripts(const char* subscripts, int length, int 
ndim, int iop,
+                                  char* op_labels, char* label_counts, int* 
min_label,
+                                  int* max_label) {
+  int i;
+  int idim = 0;
+  int ellipsis = -1;
+
+  /* Process all labels for this operand */
+  for (i = 0; i < length; ++i) {
+    int label = subscripts[i];
+
+    /* A proper label for an axis. */
+    if (label > 0 && isalpha(label)) {
+      /* Check we don't exceed the operator dimensions. */
+      CHECK(idim < ndim) << "einstein sum subscripts string contains "
+                         << "too many subscripts for operand " << iop;
+
+      op_labels[idim++] = label;
+      if (label < *min_label) {
+        *min_label = label;
+      }
+      if (label > *max_label) {
+        *max_label = label;
+      }
+      label_counts[label]++;
+    } else if (label == '.') {
+      /* The beginning of the ellipsis. */
+      /* Check it's a proper ellipsis. */
+      CHECK(
+          !(ellipsis != -1 || i + 2 >= length || subscripts[++i] != '.' || 
subscripts[++i] != '.'))
+          << "einstein sum subscripts string contains a "
+          << "'.' that is not part of an ellipsis ('...') "
+          << "in operand " << iop;
+
+      ellipsis = idim;
+    } else {
+      CHECK(label == ' ') << "invalid subscript '" << static_cast<char>(label)
+                          << "' in einstein sum "
+                          << "subscripts string, subscripts must "
+                          << "be letters";
+    }
+  }
+
+  /* No ellipsis found, labels must match dimensions exactly. */
+  if (ellipsis == -1) {
+    CHECK(idim == ndim) << "operand has more dimensions than subscripts "
+                        << "given in einstein sum, but no '...' ellipsis "
+                        << "provided to broadcast the extra dimensions.";
+  } else if (idim < ndim) {
+    /* Ellipsis found, may have to add broadcast dimensions. */
+    /* Move labels after ellipsis to the end. */
+    for (i = 0; i < idim - ellipsis; ++i) {
+      op_labels[ndim - i - 1] = op_labels[idim - i - 1];
+    }
+    /* Set all broadcast dimensions to zero. */
+    for (i = 0; i < ndim - idim; ++i) {
+      op_labels[ellipsis + i] = 0;
+    }
+  }
+
+  /*
+   * Find any labels duplicated for this operand, and turn them
+   * into negative offsets to the axis to merge with.
+   *
+   * In C, the char type may be signed or unsigned, but with
+   * twos complement arithmetic the char is ok either way here, and
+   * later where it matters the char is cast to a signed char.
+   */
+  for (idim = 0; idim < ndim - 1; ++idim) {
+    int label = op_labels[idim];
+    /* If it is a proper label, find any duplicates of it. */
+    if (label > 0) {
+      /* Search for the next matching label. */
+      char* next = reinterpret_cast<char*>(memchr(op_labels + idim + 1, label, 
ndim - idim - 1));
+
+      while (next != nullptr) {
+        /* The offset from next to op_labels[idim] (negative). */
+        *next = static_cast<char>((op_labels + idim) - next);
+        /* Search for the next matching label. */
+        next = reinterpret_cast<char*>(memchr(next + 1, label, op_labels + 
ndim - 1 - next));
+      }
+    }
+  }
+  return 0;
+}
+
+/*!
+ * \brief Parse the subscripts for the output into an output that includes 
'ndim_broadcast'
+ *        unlabeled dimensions.
+ *
+ * \param subscripts the subscripts for to be parsed.
+ * \param length subscripts[0: length] represents the output operand.
+ * \param ndim_broadcast the broadcast dimension number.
+ * \param label_counts Count the number the label appears.
+ * \param out_labels similar to the op_labels in ParseOperandSubscripts, for 
each
+ *        dimension, the ASCII code of the corresponding label. zero for the 
broadcasting dim.
+ *
+ * \return the total number of output dimensions or -1 if there is an error.
+ */
+inline int ParseOutputSubscripts(const char* subscripts, int length, int 
ndim_broadcast,
+                                 const char* label_counts, char* out_labels) {
+  int i, bdim;
+  int ndim = 0;
+  int ellipsis = 0;
+
+  /* Process all the output labels. */
+  for (i = 0; i < length; ++i) {
+    int label = subscripts[i];
+
+    /* A proper label for an axis. */
+    if (label > 0 && isalpha(label)) {
+      /* Check that it doesn't occur again. */
+      CHECK(memchr(subscripts + i + 1, label, length - i - 1) == nullptr)
+          << "einstein sum subscripts string includes "
+          << "output subscript '" << static_cast<char>(label) << "' multiple 
times";
+
+      /* Check that it was used in the inputs. */
+      CHECK(label_counts[label] != 0)
+          << "einstein sum subscripts string included "
+          << "output subscript '" << static_cast<char>(label) << "' which 
never appeared "
+          << "in an input";
+
+      /* Check that there is room in out_labels for this label. */
+      CHECK(ndim < 16) << "einstein sum subscripts string contains "
+                       << "too many subscripts in the output";
+
+      out_labels[ndim++] = label;
+    } else if (label == '.') {
+      /* The beginning of the ellipsis. */
+      /* Check it is a proper ellipsis. */
+      CHECK(!(ellipsis || i + 2 >= length || subscripts[++i] != '.' || 
subscripts[++i] != '.'))
+          << "einstein sum subscripts string "
+          << "contains a '.' that is not part of "
+          << "an ellipsis ('...') in the output";
+
+      /* Check there is room in out_labels for broadcast dims. */
+      CHECK(ndim + ndim_broadcast <= 16) << "einstein sum subscripts string 
contains "
+                                         << "too many subscripts in the 
output";
+
+      ellipsis = 1;
+      for (bdim = 0; bdim < ndim_broadcast; ++bdim) {
+        out_labels[ndim++] = 0;
+      }
+    } else {
+      CHECK(label == ' ') << "invalid subscript '" << static_cast<char>(label)
+                          << "' in einstein sum "
+                          << "subscripts string, subscripts must "
+                          << "be letters";
+    }
+  }
+
+  /* If no ellipsis was found there should be no broadcast dimensions. */
+  CHECK(!(!ellipsis && ndim_broadcast > 0)) << "output has more dimensions 
than subscripts "
+                                            << "given in einstein sum, but no 
'...' ellipsis "
+                                            << "provided to broadcast the 
extra dimensions.";
+
+  return ndim;
+}
+
+/*!
+ * \brief If any dimensions are combined, create a view that combines them.
+ *        Shows in newshape and newstride.
+ *
+ * \param op the operand tensor.
+ * \param iop the index of the operand.
+ * \param labels the op_labels fot the operand. Like [97, 98, -2] for "aba".
+ * \param newshape The combined shape.
+ * \param newstride The combined stride.
+ *
+ * For example:
+ *  "aba -> ab",              shape = [2,3,2] stride = [6,2,1]
+ *  op_labels = [97, 98, -2], newshape = [2,3], newstride = [7,2]
+ */
+inline void GetCombinedDimsView(const Tensor& op, int iop, char* labels, 
Array<PrimExpr>* newshape,
+                                Array<PrimExpr>* newstride) {
+  int idim, ndim, icombine, combineoffset;
+  int icombinemap[16];
+  int newdim;
+
+  Array<PrimExpr> shape = op->shape;
+  Array<PrimExpr> stride = GetStride(shape);
+  ndim = op.ndim();
+  newdim = newshape->size();
+
+  /* Initialize the dimensions and strides to zero */
+  for (idim = 0; idim < newdim; ++idim) {
+    newshape->Set(idim, 0);
+    newstride->Set(idim, 0);
+  }
+
+  /* Copy the dimensions and strides, except when collapsing */
+  icombine = 0;
+  for (idim = 0; idim < ndim; ++idim) {
+    /*
+     * The char type may be either signed or unsigned, we
+     * need it to be signed here.
+     */
+    int label = (signed char)labels[idim];
+    /* If this label says to merge axes, get the actual label */
+    if (label < 0) {
+      combineoffset = label;
+      label = labels[idim + label];
+    } else {
+      combineoffset = 0;
+      if (icombine != idim) {
+        labels[icombine] = labels[idim];
+      }
+      icombinemap[idim] = icombine;
+    }
+    /* If the label is 0, it's an unlabeled broadcast dimension */
+    if (label == 0) {
+      newshape->Set(icombine, shape[idim]);
+      newstride->Set(icombine, stride[idim]);
+    } else {
+      /* Update the combined axis dimensions and strides */
+      int i = icombinemap[idim + combineoffset];
+      CHECK(!((combineoffset < 0) &&
+              GetConstInt((*newshape)[i] != 0 && (*newshape)[i] != 
shape[idim])))
+          << "dimensions in operand " << iop << " for collapsing index '" << 
label
+          << "' don't match (" << GetConstInt((*newshape)[i]) << " != " << 
shape[idim] << ")";
+      newshape->Set(i, shape[idim]);
+      newstride->Set(i, (*newstride)[i] + stride[idim]);
+    }
+
+    /* If the label didn't say to combine axes, increment dest i */
+    if (combineoffset == 0) {
+      icombine++;
+    }
+  }
+}
+
+/*!
+ * \brief Prepare the operand axes to match each stride or shape pair.
+ *
+ * \param ndim the ndim of the operand tensor.
+ * \param iop the index of the operand.
+ * \param labels the op_labels fot the operand. [97, 98, -1, 99, -3, -2] for 
"abbcbc".
+ * \param axes The matched axes to be calculated.
+ * \param ndim_iter the dimension of iterating. Subscripts "ab, bc -> ac" 
ndim_iter = 3.
+ * \param iter_labels output_labels with the iterating label. ['a', 'c', 'b'] 
for the case above.
+ */
+inline static int PrepareOpAxes(int ndim, int iop, char* labels, int* axes, 
int ndim_iter,
+                                char* iter_labels) {
+  int i, label, ibroadcast;
+
+  ibroadcast = ndim - 1;
+  for (i = ndim_iter - 1; i >= 0; --i) {
+    label = iter_labels[i];
+    /*
+     * If it's an unlabeled broadcast dimension, choose
+     * the next broadcast dimension from the operand.
+     */
+    if (label == 0) {
+      while (ibroadcast >= 0 && labels[ibroadcast] != 0) {
+        --ibroadcast;
+      }
+      /*
+       * If we used up all the operand broadcast dimensions,
+       * extend it with a "newaxis"
+       */
+      if (ibroadcast < 0) {
+        axes[i] = -1;
+      } else {
+        /* Otherwise map to the broadcast axis */
+        axes[i] = ibroadcast;
+        --ibroadcast;
+      }
+    } else {
+      /* It's a labeled dimension, find the matching one */
+      char* match = reinterpret_cast<char*>(memchr(labels, label, ndim));
+      /* If the op doesn't have the label, broadcast it */
+      if (match == nullptr) {
+        axes[i] = -1;
+      } else {
+        /* Otherwise use it */
+        axes[i] = match - labels;
+      }
+    }
+  }
+  return 0;
+}
+
+/*!
+ * \brief Count SubString.
+ * \param str the object string
+ * \param sub the pattern string
+ *
+ * \return number of substring
+ */
+inline int CountSubstring(const std::string& str, const std::string& sub) {
+  int count = 0;
+  std::string::size_type pos = 0;
+  while ((pos = str.find(sub, pos)) != std::string::npos) {
+    ++count;
+    pos += sub.length();
+  }
+  return count;
+}
+
+/*!
+ * \brief Transfer string to.
+ * \param str input string.
+ *
+ * \return bitset.
+ */
+inline std::bitset<128> Str2Set(const std::string& str) {
+  std::bitset<128> ret;
+  for (const char& c : str) {
+    ret.set(static_cast<int>(c));
+  }
+  return ret;
+}
+
+/*!
+ * \brief Split str according to substring.
+ * \param str input string.
+ * \param sub the split pattern string.
+ *
+ * \return vector contains the splited substring.
+ */
+inline std::vector<std::string> Split(const std::string& str, const 
std::string& sub) {
+  std::string::size_type pos = 0;
+  std::string::size_type start = 0;
+  std::vector<std::string> ret;
+  while ((pos = str.find(sub, start)) != std::string::npos) {
+    ret.push_back(str.substr(start, pos - start));
+    start = pos + sub.length();
+  }
+  ret.push_back(str.substr(start));
+  return ret;
+}
+
+/*!
+ * \brief Parse the input subscripts into a vector of strings.
+ * \param subscripts input subscripts.
+ * \param operands operand tensors.
+ *
+ * \return vector of strings, vector[0] represents the input part, vector[1] 
represents the ouput.
+ * if no output, the vector[1] is NULL.
+ * "ab, bc -> ac" => ["ab,bc", "ac"]
+ */
+inline std::vector<std::string> ParseEinsumInput(std::string subscripts,
+                                                 const 
std::vector<Array<PrimExpr>>& operands) {
+  const std::string einsum_symbols = 
"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+  std::bitset<128> einsum_symbols_set;
+  for (const char& c : einsum_symbols) {
+    einsum_symbols_set.set(c);
+  }
+
+  CHECK_NE(operands.size(), 0U) << "No input operands";
+
+  auto end_pos = std::remove(subscripts.begin(), subscripts.end(), ' ');
+  subscripts.erase(end_pos, subscripts.end());
+
+  // Ensure all characters are valid
+  for (const char& c : subscripts) {
+    if (c == '.' || c == ',' || c == '-' || c == '>') {
+      continue;
+    }
+    CHECK(einsum_symbols_set.test(c)) << "Character " << c << " is not a valid 
symbol.";
+  }
+
+  // Check for proper "->"
+  if (subscripts.find('-') != std::string::npos || subscripts.find('>') != 
std::string::npos) {
+    bool invalid = (std::count(subscripts.begin(), subscripts.end(), '-') > 1 
||
+                    std::count(subscripts.begin(), subscripts.end(), '>') > 1);
+    CHECK(!invalid && CountSubstring(subscripts, "->") == 1)
+        << "Subscripts can only contain one '->'.";
+  }
+
+  // Parse ellipses
+  if (subscripts.find('.') != std::string::npos) {
+    std::string used = subscripts;
+    used.erase(
+        std::remove_if(used.begin(), used.end(),
+                       [](const char& c) { return c == '.' || c == ',' || c == 
'-' || c == '>'; }),
+        used.end());
+
+    std::bitset<128> used_set = Str2Set(used);
+    std::string ellipse_inds = "";
+    for (const char& c : einsum_symbols) {
+      if (!used_set.test(static_cast<int>(c))) {
+        ellipse_inds.append(1, c);
+      }
+    }
+    int longest = 0;
+    std::string input_tmp, output_sub;
+    std::vector<std::string> split_subscripts;
+    bool out_sub;
+
+    if (subscripts.find("->") != std::string::npos) {
+      std::vector<std::string> tmp = Split(subscripts, "->");
+      input_tmp = tmp[0];
+      output_sub = tmp[1];
+      split_subscripts = Split(input_tmp, ",");
+      out_sub = true;
+    } else {
+      split_subscripts = Split(subscripts, ",");
+      out_sub = false;
+    }
+
+    size_t size_split_subscripts = split_subscripts.size();
+    subscripts = "";
+    for (size_t i = 0; i < size_split_subscripts; ++i) {
+      const std::string& sub = split_subscripts[i];
+      if (sub.find('.') != std::string::npos) {
+        CHECK_EQ(std::count(sub.begin(), sub.end(), '.'), 3) << "Invalid 
Ellipses";
+        CHECK_EQ(CountSubstring(sub, "..."), 1) << "Invalid Ellipses";
+
+        // Take into account numerical values
+        int ellipse_count = 0;
+        if (operands[i].size() == 0) {
+          ellipse_count = 0;
+        } else {
+          ellipse_count = std::max(operands[i].size(), static_cast<size_t>(1));
+          ellipse_count -= sub.length() - 3;
+        }
+
+        if (ellipse_count > longest) {
+          longest = ellipse_count;
+        }
+
+        CHECK_GE(ellipse_count, 0) << "Ellipses lengths do not match.";
+        if (ellipse_count == 0) {
+          split_subscripts[i].erase(sub.find("..."), 3);
+        } else {
+          std::string rep_inds = ellipse_inds.substr(ellipse_inds.length() - 
ellipse_count);
+          split_subscripts[i].replace(sub.find("..."), 3, rep_inds);
+        }
+      }
+      subscripts += split_subscripts[i];
+      if (i + 1 < size_split_subscripts) {
+        subscripts += ",";
+      }
+    }
+    std::string out_ellipse;
+    if (longest == 0) {
+      out_ellipse = "";
+    } else {
+      out_ellipse = ellipse_inds.substr(ellipse_inds.length() - longest);
+    }
+
+    if (out_sub) {
+      output_sub.replace(output_sub.find("..."), 3, out_ellipse);
+      subscripts += "->" + output_sub;
+    } else {
+      // Special care for outputless ellipses
+      std::bitset<128> out_ellipse_set = Str2Set(out_ellipse);
+      std::string tmp_subscripts = subscripts, output_subscript = "";
+      size_t len_tmp_subscripts = tmp_subscripts.length();
+      std::sort(tmp_subscripts.begin(), tmp_subscripts.end());
+      for (size_t i = 0; i < len_tmp_subscripts; ++i) {
+        const char& c = tmp_subscripts[i];
+        if (c == ',') {
+          continue;
+        }
+        CHECK(einsum_symbols_set.test(c)) << "Character " << c << " is not a 
valid symbol.";
+        if ((i == 0 || tmp_subscripts[i - 1] != c) &&
+            (i == len_tmp_subscripts - 1 || tmp_subscripts[i + 1] != c) &&
+            !out_ellipse_set.test(c)) {
+          output_subscript.append(1, c);
+        }
+      }
+      subscripts += "->" + out_ellipse + output_subscript;
+    }
+  }
+
+  // Build output string if does not exist
+  std::vector<std::string> ret(2);
+  if (subscripts.find("->") != std::string::npos) {
+    ret = Split(subscripts, "->");
+  } else {
+    ret[0] = subscripts;
+    ret[1] = "";
+    // Build output subscripts
+    std::string tmp_subscripts = subscripts;
+    size_t len_tmp_subscripts = tmp_subscripts.length();
+    std::sort(tmp_subscripts.begin(), tmp_subscripts.end());
+    for (size_t i = 0; i < len_tmp_subscripts; ++i) {
+      const char& c = tmp_subscripts[i];
+      if (c == ',') {
+        continue;
+      }
+      CHECK(einsum_symbols_set.test(c)) << "Character " << c << " is not a 
valid symbol.";
+      if ((i == 0 || tmp_subscripts[i - 1] != c) &&
+          (i == len_tmp_subscripts - 1 || tmp_subscripts[i + 1] != c)) {
+        ret[1].append(1, c);
+      }
+    }
+  }
+
+  // Make sure output subscripts are in the input
+  std::bitset<128> input_subscripts_set = Str2Set(ret[0]);
+  for (const char& c : ret[1]) {
+    CHECK(input_subscripts_set.test(c))
+        << "Output character " << c << " did not appear in the input";
+  }
+
+  // Make sure number operands is equivalent to the number of terms
+  CHECK_EQ(std::count(ret[0].begin(), ret[0].end(), ',') + 1, operands.size())
+      << "Number of einsum subscripts must be equal to the "
+      << "number of operands.";
+
+  return ret;
+}
+
+/*!
+ * \brief Compute the shape of the output.
+ * \param subscripts input subscripts.
+ * \param operands operand tensors.
+ *
+ * \return the shape of the output.
+ */
+inline Array<PrimExpr> NumpyEinsumShape(const std::string subscripts,
+                                        const std::vector<Array<PrimExpr>>& 
operands) {
+  // Parsing
+  std::vector<std::string> parsed_subscripts = ParseEinsumInput(subscripts, 
operands);
+
+  // Build a few useful list and sets
+  std::vector<std::string> input_list = Split(parsed_subscripts[0], ",");
+  size_t isize = input_list.size();
+
+  // Get length of each unique dimension and ensure all dimensions are correct
+  int dimension_dict[128];
+  memset(dimension_dict, -1, sizeof(dimension_dict));
+  for (size_t i = 0; i < isize; ++i) {
+    const std::string& term = input_list[i];
+    const Array<PrimExpr>& sh = operands[i];
+    CHECK_EQ(sh.size(), term.length())
+        << "Einstein sum subscript " << input_list[i] << " does not contain 
the "
+        << "correct number of indices for operand " << i << ".";
+    size_t len_term = term.length();
+    for (size_t j = 0; j < len_term; ++j) {
+      int64_t dim = GetConstInt(sh[j]);
+      const char& c = term[j];
+
+      if (dimension_dict[static_cast<int>(c)] != -1) {
+        // For broadcasting cases we always want the largest dim size
+        if (dimension_dict[static_cast<int>(c)] == 1) {
+          dimension_dict[static_cast<int>(c)] = dim;
+        }
+        CHECK(dim == 1 || dim == dimension_dict[static_cast<int>(c)])
+            << "Size of label '" << c << "' for operand  " << i << " ("
+            << dimension_dict[static_cast<int>(c)] << ") does not match 
previous terms (" << dim
+            << ").";
+      } else {
+        dimension_dict[static_cast<int>(c)] = dim;
+      }
+    }
+  }
+
+  // Get oshape
+  const std::string& output_str = parsed_subscripts[1];
+  size_t odim = output_str.size();
+  Array<PrimExpr> oshape(odim, -1);
+  for (size_t i = 0; i < odim; ++i) {
+    oshape.Set(i, dimension_dict[static_cast<int>(output_str[i])]);
+  }
+  // Neglecting oshape assign check temporally
+  return oshape;
+}
+
+/*!
+ * \brief Evaluates the Einstein summation convention on the operands.
+ *
+ * \param subscripts_str Specifies the subscripts for summation as comma 
separated list of subscript
+ * labels. \param inputs Arrays for the operation. \param name The name of the 
operation. \param tag
+ * The tag to mark the operation.
+ *
+ * \return The calculation based on the Einstein summation convention.
+ */
+inline Tensor einsum(const std::string& subscripts_str, const Array<Tensor> 
inputs,
+                     std::string name = "T_einsum", std::string tag = kMatMul) 
{
+  // able to compute op: trace, diag, sum, transpose, matmul, dot, inner, 
outer, multiply, tensordot
+  bool back = false;
+  const char* subscripts = subscripts_str.data();
+  const int nop = inputs.size();
+
+  /* Step 1: Parse the subscripts string into label_counts and op_labels */
+  int iop, idim, min_label = 127, max_label = 0;
+  char label_counts[128], op_labels[16][16];
+  memset(label_counts, 0, sizeof(label_counts));
+  for (iop = 0; iop < nop; ++iop) {
+    int length = static_cast<int>(strcspn(subscripts, ",-"));
+
+    CHECK(!(iop == nop - 1 && subscripts[length] == ','))
+        << "more operands provided to einstein sum function "
+        << "than specified in the subscripts string";
+    CHECK(!(iop < nop - 1 && subscripts[length] != ','))
+        << "fewer operands provided to einstein sum function "
+        << "than specified in the subscripts string";
+    ParseOperandSubscripts(subscripts, length, inputs[iop + back].ndim(), iop, 
op_labels[iop],

Review comment:
       Added Check. Thx!




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