Integrate llvm/llvm-project@bc81f8c87e (#15556)

This commit bumps the LLVM submodule to
-
[llvm/llvm-project@bc81f8c87e](llvm/llvm-project@bc81f8c)

compiler/src/iree/compiler/Codegen/LLVMGPU/test/attention.mlir

@@ -163,7 +163,6 @@ hal.executable @_attention_dispatch_0 {
 // CHECK:        vector.transfer_write %[[D12]], %[[ALLOC_7]][%[[C0]], %[[D8]], %[[C0]]] {in_bounds = [true, true]} :
 // CHECK-SAME:     vector<32x64xf16>, memref<1x128x64xf16, #[[GPU]].address_space<workgroup>>
 // CHECK:        gpu.barrier
-// CHECK:        gpu.barrier
 // CHECK:        linalg.generic {indexing_maps = [#[[MAP1]], #[[MAP1]]], iterator_types = ["parallel", "parallel",
 // CHECK-SAME:     "parallel"]} ins(%[[ALLOC_7]] : memref<1x128x64xf16, #[[GPU]].address_space<workgroup>>)
 // CHECK-SAME:     outs(%[[SUBVIEW_6]] : memref<1x128x64xf16, strided<[65536, 64, 1], offset: ?>, #hal.descriptor_type<storage_buffer>>) {

tests/transform_dialect/cpu/contraction-packing-and-dispatch.mlir

@@ -25,7 +25,6 @@
 //       CHECK:   tensor.pack
 
 // CHECK-LABEL: func.func @matmul_dispatch_1
-//       CHECK:   arith.constant dense<1.000000e-01> : tensor<567x890xf32>
 //       CHECK:   tensor.empty() : tensor<18x56x16x32xf32>
 //       CHECK:   tensor.pack
 
@@ -35,7 +34,8 @@
 
 // CHECK-LABEL: func.func @matmul_dispatch_3
 func.func @matmul(%arg0: !a_tensor_t, %arg2: !c_tensor_t) -> !c_tensor_t {
-  %c0 = arith.constant dense<0.1> : !b_tensor_t
+  %rhs = arith.constant dense<0.1> : !b_tensor_t
+  %c0 = util.optimization_barrier %rhs : !b_tensor_t
   //  CHECK-NOT: pack
   //      CHECK: linalg.generic {indexing_maps = [#[[$map_lhs]], #[[$map_rhs]], #[[$map_res]]],
   // CHECK-SAME:   iterator_types = ["parallel", "parallel", "parallel", "parallel", "reduction", "reduction"]}