[GitHub] [tvm] tqchen commented on a change in pull request #9023: [TE] Support negative indices

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

tqchen commented on a change in pull request #9023:
URL: https://github.com/apache/tvm/pull/9023#discussion_r709643444



##########
File path: src/te/tensor.cc
##########
@@ -39,15 +39,26 @@ IterVar reduce_axis(Range dom, std::string name) { return IterVar(dom, Var(name)
 Var var(std::string name_hint, DataType t) { return Var(name_hint, t); }
 
 // Tensor
-PrimExpr Tensor::operator()(Array<Var> indices) const {
+PrimExpr Tensor::operator()(Array<Var> indices, bool support_negative_indices = false) const {
   Array<PrimExpr> arr(indices.begin(), indices.end());
-  return operator()(arr);
+  return operator()(arr, support_negative_indices);
 }
 
-PrimExpr Tensor::operator()(Array<PrimExpr> indices) const {
-  if (ndim() != 0) {
-    ICHECK_EQ(ndim(), indices.size()) << "Tensor dimension mismatch in read "
-                                      << "ndim = " << ndim() << ", indices.size=" << indices.size();
+PrimExpr Tensor::operator()(Array<PrimExpr> indices, bool support_negative_indices = false) const {
+  Array<PrimExpr> shape = (*this)->shape;
+
+  if (shape.size() != 0) {
+    ICHECK_EQ(shape.size(), indices.size())
+        << "Tensor dimension mismatch in read "
+        << "ndim = " << ndim() << ", indices.size=" << indices.size();
+  }
+
+  if (support_negative_indices) {
+    for (size_t i = 0; i < shape.size(); i++) {
+      PrimExpr new_index = if_then_else(indices[i] < make_const(indices[i]->dtype, 0),

Review comment:
       you want to use select here, because it does not involves a memory operation(thus can evaluate both sides)




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