[XLA] Turn constant dynamic slices into slices.

PiperOrigin-RevId: 308358674
Change-Id: I92f1674325c4824f858b1183455135e97e44bebc

tensorflow/compiler/xla/BUILD

@@ -449,7 +449,6 @@ cc_library(
         "@com_google_absl//absl/memory",
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/strings:str_format",
-        "@com_google_absl//absl/types:optional",
         "@com_google_absl//absl/types:span",
     ],
 )

tensorflow/compiler/xla/literal.cc

@@ -27,7 +27,6 @@ limitations under the License.
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_format.h"
 #include "absl/strings/str_join.h"
-#include "absl/types/optional.h"
 #include "absl/types/span.h"
 #include "tensorflow/compiler/xla/index_util.h"
 #include "tensorflow/compiler/xla/primitive_util.h"
@@ -199,34 +198,6 @@ Literal LiteralBase::CreateFromShape(const Shape& shape) {
   return literal;
 }
 
-absl::optional<int64> LiteralBase::GetFirstInteger() const {
-  switch (shape().element_type()) {
-    case U8:
-      return GetFirstElement<uint8>();
-    case U16:
-      return GetFirstElement<uint16>();
-    case U32:
-      return GetFirstElement<uint32>();
-    case U64: {
-      int64 v = GetFirstElement<uint64>();
-      if (v < 0) {
-        return absl::nullopt;
-      }
-      return v;
-    }
-    case S8:
-      return GetFirstElement<int8>();
-    case S16:
-      return GetFirstElement<int16>();
-    case S32:
-      return GetFirstElement<int32>();
-    case S64:
-      return GetFirstElement<int64>();
-    default:
-      return absl::nullopt;
-  }
-}
-
 template <typename NativeT>
 Status MutableLiteralBase::CopySliceFromInternal(
     const LiteralBase& src_literal, absl::Span<const int64> src_base,

tensorflow/compiler/xla/literal.h

@@ -27,7 +27,6 @@ limitations under the License.
 
 #include "absl/memory/memory.h"
 #include "absl/strings/string_view.h"
-#include "absl/types/optional.h"
 #include "absl/types/span.h"
 #include "tensorflow/compiler/xla/array2d.h"
 #include "tensorflow/compiler/xla/array3d.h"
@@ -117,9 +116,6 @@ class LiteralBase {
   template <typename NativeT>
   NativeT GetFirstElement() const;
 
-  // As above but returns any integer type casted to an int64.
-  absl::optional<int64> GetFirstInteger() const;
-
   // As Get(), but determines the correct type and converts the value
   // into text.
   string GetAsString(absl::Span<const int64> multi_index,

tensorflow/compiler/xla/service/algebraic_simplifier.cc

@@ -816,8 +816,6 @@ Status AlgebraicSimplifierVisitor::HandleAdd(HloInstruction* add) {
     // Concatenate the indices and updates
     if (index_concat_is_safe && same_dimension_numbers &&
         index_concat_dimension &&
-        lhs_scatter_index->shape().element_type() ==
-            rhs_scatter_index->shape().element_type() &&
         ShapeUtil::SameDimensions(lhs_update_window, rhs_update_window)) {
       TF_ASSIGN_OR_RETURN(HloInstruction * new_operand,
                           MakeBinaryHlo(HloOpcode::kAdd, lhs_scatter_operand,
@@ -3638,39 +3636,6 @@ Status AlgebraicSimplifierVisitor::HandleDynamicSlice(
         MakeBroadcastHlo(new_dynamic_slice, operand->dimensions(),
                          dynamic_slice->shape()));
   }
-
-  // Convert a dynamic slice into a slice if all offsets are  constant and the
-  // operand is not constant. If ev
-  if (operand->opcode() != HloOpcode::kConstant &&
-      absl::c_all_of(absl::MakeSpan(dynamic_slice->operands().begin() + 1,
-                                    dynamic_slice->operands().end()),
-                     [](HloInstruction* operand) {
-                       return operand->opcode() == HloOpcode::kConstant &&
-                              ShapeUtil::ElementIsIntegral(operand->shape());
-                     })) {
-    const int64 rank = operand->shape().rank();
-    std::vector<int64> slice_starts(rank);
-    std::vector<int64> slice_limits(rank);
-    std::vector<int64> slice_strides(rank, 1);
-
-    for (int64 i = 0; i < rank; ++i) {
-      absl::optional<int64> offset =
-          dynamic_slice->operand(i + 1)->literal().GetFirstInteger();
-      if (!offset || *offset < 0) {
-        return Status::OK();
-      }
-      const int64 max_offset =
-          dynamic_slice->operand(0)->shape().dimensions(i) -
-          dynamic_slice->shape().dimensions(i);
-      slice_starts[i] = std::min(max_offset, *offset);
-      slice_limits[i] =
-          std::min(max_offset, *offset) + dynamic_slice->shape().dimensions(i);
-    }
-    return ReplaceWithNewInstruction(
-        dynamic_slice,
-        HloInstruction::CreateSlice(dynamic_slice->shape(), operand,
-                                    slice_starts, slice_limits, slice_strides));
-  }
   return Status::OK();
 }
 
@@ -3705,8 +3670,8 @@ Status AlgebraicSimplifierVisitor::HandleDynamicUpdateSlice(
         compatible = false;
       }
     }
-    PaddingConfig padding_config;
     if (compatible) {
+      PaddingConfig padding_config;
       for (int64 dim = 0; dim < updated_shape.rank(); ++dim) {
         auto padding_config_dim = padding_config.add_dimensions();
         auto slice_dim_start = update_start_indx->operand(dim + offset);
@@ -3715,23 +3680,24 @@ Status AlgebraicSimplifierVisitor::HandleDynamicUpdateSlice(
           break;
         }
         VLOG(2) << "slice :" << slice_dim_start->ToString();
-        absl::optional<int64> beg =
-            slice_dim_start->literal().GetFirstInteger();
-        if (!beg) {
+        int64 beg;
+        if (slice_dim_start->shape().element_type() == S32) {
+          beg = slice_dim_start->literal().Get<int32>({});
+        } else if (slice_dim_start->shape().element_type() == U32) {
+          beg = slice_dim_start->literal().Get<uint32>({});
+        } else {
           compatible = false;
           break;
         }
-        VLOG(2) << "beg value:" << *beg;
+        VLOG(2) << "beg value:" << beg;
         auto update_width = ShapeUtil::GetDimension(update_shape, dim);
         auto bcast_width = ShapeUtil::GetDimension(updated_shape, dim);
-        padding_config_dim->set_edge_padding_low(*beg);
+        padding_config_dim->set_edge_padding_low(beg);
         padding_config_dim->set_edge_padding_high(
-            std::max(bcast_width - (*beg + update_width), int64{0}));
+            std::max(bcast_width - (beg + update_width), int64{0}));
         // dynamic_update_slice does not specify a stride
         padding_config_dim->set_interior_padding(0);
       }
-    }
-
       if (compatible) {
         HloInstruction* pad =
             computation_->AddInstruction(HloInstruction::CreatePad(
@@ -3740,7 +3706,11 @@ Status AlgebraicSimplifierVisitor::HandleDynamicUpdateSlice(
         VLOG(2) << " with pad:" << pad->ToString();
         VLOG(2) << " Computation before rewrite is: "
                 << dynamic_update_slice->parent()->ToString();
-      return ReplaceInstruction(dynamic_update_slice, pad);
+        auto res = ReplaceInstruction(dynamic_update_slice, pad);
+        VLOG(2) << " Computation after rewrite is: "
+                << pad->parent()->ToString();
+        return res;
+      }
     }
   }
 

tensorflow/compiler/xla/service/algebraic_simplifier_test.cc

@@ -4183,31 +4183,6 @@ TEST_F(AlgebraicSimplifierTest, TrivialDynamicSlice) {
   EXPECT_THAT(computation->root_instruction(), GmockMatch(m::Parameter()));
 }
 
-TEST_F(AlgebraicSimplifierTest, ConstantDynamicSlice) {
-  auto m = CreateNewVerifiedModule();
-  HloComputation::Builder builder(TestName());
-
-  Shape shape = ShapeUtil::MakeShape(F32, {10, 100, 1000});
-  std::vector<HloInstruction*> params;
-  for (int i = 0; i < 3; ++i) {
-    params.push_back(builder.AddInstruction(HloInstruction::CreateConstant(
-        LiteralUtil::CreateR0<int32>(2 << (i + 1)))));
-  }
-  Shape ds_shape = ShapeUtil::MakeShape(F32, {2, 20, 200});
-  builder.AddInstruction(HloInstruction::CreateDynamicSlice(
-      ds_shape,
-      builder.AddInstruction(
-          HloInstruction::CreateParameter(0, shape, "operand")),
-      params,
-      /*slice_sizes=*/{2, 20, 200}));
-
-  auto computation = m->AddEntryComputation(builder.Build());
-  AlgebraicSimplifier simplifier(default_options_);
-  ASSERT_TRUE(simplifier.Run(m.get()).ValueOrDie());
-  EXPECT_THAT(computation->root_instruction(),
-              GmockMatch(m::Slice(m::Parameter())));
-}
-
 // A dynamic-update-slice is trivial if its start indices are all zeroes and the
 // size of its "update" equals the size of its output.  In this case, the
 // dynamic-update-slice is equal to its update.