[XLA] Document DynamicSlice and DynamicUpdateSlice semantics.

PiperOrigin-RevId: 205858924

1 files changed, 22 insertions, 4 deletions

diff --git a/tensorflow/docs_src/performance/xla/operation_semantics.md b/tensorflow/docs_src/performance/xla/operation_semantics.md
index d6fa8ab5f9..26a7b9e42c 100644
--- a/tensorflow/docs_src/performance/xla/operation_semantics.md
+++ b/tensorflow/docs_src/performance/xla/operation_semantics.md
@@ -791,8 +791,6 @@ DynamicSlice extracts a sub-array from the input array at dynamic
 `size_indices`, which specify the end point of exclusive slice intervals in each
 dimension: [start, start + size). The shape of `start_indices` must be rank ==
 1, with dimension size equal to the rank of `operand`.
-Note: handling of out-of-bounds slice indices (generated by incorrect runtime
-calculation of 'start_indices') is currently implementation-defined.
 
 <b> `DynamicSlice(operand, start_indices, size_indices)` </b>
 
@@ -812,6 +810,17 @@ calculation of 'start_indices') is currently implementation-defined.
 :                 :                     : dimension to avoid wrapping modulo  :
 :                 :                     : dimension size.                     :
 
+The effective slice indices are computed by applying the following
+transformation for each index `i` in `[1, N)` before performing the slice:
+
+```
+start_indices[i] = clamp(start_indices[i], 0, operand.dimension_size[i] - size_indices[i])
+```
+
+This ensures that the extracted slice is always in-bounds with respect to the
+operand array. If the slice is in-bounds before the transformation is applied,
+the transformation has no effect.
+
 1-dimensional example:
 
 ```
@@ -847,8 +856,6 @@ The shape of `update` determines the shape of the sub-array of the result which
 is updated.
 The shape of `start_indices` must be rank == 1, with dimension size equal to
 the rank of `operand`.
-Note: handling of out-of-bounds slice indices (generated by incorrect runtime
-calculation of 'start_indices') is currently implementation-defined.
 
 <b> `DynamicUpdateSlice(operand, update, start_indices)` </b>
 
@@ -866,6 +873,17 @@ calculation of 'start_indices') is currently implementation-defined.
 :                 :         : dimension. Value must be greater than or equal   :
 :                 :         : to zero.                                         :
 
+The effective slice indices are computed by applying the following
+transformation for each index `i` in `[1, N)` before performing the slice:
+
+```
+start_indices[i] = clamp(start_indices[i], 0, operand.dimension_size[i] - update.dimension_size[i])
+```
+
+This ensures that the updated slice is always in-bounds with respect to the
+operand array. If the slice is in-bounds before the transformation is applied,
+the transformation has no effect.
+
 1-dimensional example:
 
 ```