Improve our handling of bitcasts.

 - Do not fuse bitcasts in the CPU backend.  Fused instructions lose their
   layout and a bitcast is meaningless without a layout.  We were explicitly
   testing for this so I've changed the corresponding tests to use a reshape
   instead.
 - Fail the layout assignment if we see a bitcast.  bitcasts are inherently
   layout sensitive and so a bitcast instruction present in the IR before layout
   assignment is a bug.

PiperOrigin-RevId: 187210151

1 files changed, 21 insertions, 0 deletions

diff --git a/tensorflow/compiler/xla/service/layout_assignment_test.cc b/tensorflow/compiler/xla/service/layout_assignment_test.cc
index 62feb7c1e9..4b1c9bad41 100644
--- a/tensorflow/compiler/xla/service/layout_assignment_test.cc
+++ b/tensorflow/compiler/xla/service/layout_assignment_test.cc
@@ -796,5 +796,26 @@ TEST_F(LayoutAssignmentTest, ConditionalAsymmetricLayout) {
   EXPECT_THAT(false_result->opcode(), HloOpcode::kCopy);
 }
 
+TEST_F(LayoutAssignmentTest, InternalErrorOnBitcast) {
+  auto builder = HloComputation::Builder(TestName());
+  auto constant0 = builder.AddInstruction(
+      HloInstruction::CreateConstant(Literal::CreateR2WithLayout<float>(
+          {{1.0, 2.0}, {3.0, 4.0}}, LayoutUtil::MakeLayout({0, 1}))));
+  builder.AddInstruction(HloInstruction::CreateUnary(
+      constant0->shape(), HloOpcode::kBitcast, constant0));
+  auto module = CreateNewModule();
+  module->AddEntryComputation(builder.Build());
+
+  ComputationLayout computation_layout(
+      module->entry_computation()->ComputeProgramShape());
+  LayoutAssignment layout_assignment(&computation_layout);
+  Status error_status = layout_assignment.Run(module.get()).status();
+  EXPECT_FALSE(error_status.ok());
+  EXPECT_THAT(
+      error_status.error_message(),
+      ::testing::HasSubstr(
+          "Unexpected bitcast operation seen during layout assignment"));
+}
+
 }  // namespace
 }  // namespace xla