message: [XLA/GPU] Test column reduction vectorization
  Test that the IR we produce for column reduction is actually vectorized.
  Surprisingly, this was not actually tested before.
diff: @@ -766,6 +766,30 @@ TEST_F(GpuKernelTilingTest, RowReductionRequiring64BitIndex) {
  /*match_optimized_ir=*/true);
  }
  +TEST_F(GpuKernelTilingTest, ColumnReductionVectorization) {
  + const char *const kHloString = R"(
  +HloModule column_reduce_powerof2
  +
  +reduction {
  + x = f32[] parameter(0)
  + y = f32[] parameter(1)
  + ROOT add = f32[] add(x, y)
  +}
  +
  +ENTRY kernel_entry {
  + constant0 = f32[] constant(0)
  + arg1 = f32[1024,512]{1,0} parameter(0)
  + ROOT reduce = f32[512]{0} reduce(arg1, constant0), dimensions={0}, to_apply=reduction
  +}
  + )";
  + auto expected_ir = R"(
  +; CHECK: load <2 x float>, <2 x float>
  + )";
  + auto hlo_module = ParseAndReturnVerifiedModule(kHloString).ValueOrDie();
  + CompileAndVerifyIr(std::move(hlo_module), expected_ir,
  + /*match_optimized_ir=*/true);
  +}
  +
  } // namespace
  } // namespace gpu
  } // namespace xla
  