[SYCL] Add regression test for local_accessor 3D subscript (intel/llvm-test-suite#1191)

Adds a regression test checking that the subscript operator on a
3-dimensional local_accessor compiles and runs as expected.

This is related to intel#6669

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

SYCL/Regression/local_accessor_3d_subscript.cpp

@@ -0,0 +1,35 @@
+// RUN: %clangxx -fsycl -fsycl-targets=%sycl_triple %s -o %t.out
+// RUN: %CPU_RUN_PLACEHOLDER %t.out
+// RUN: %GPU_RUN_PLACEHOLDER %t.out
+
+//==------------------ local_accessor_3d_subscript.cpp ---------------------==//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// Tests that the subscript operator on a 3-dimensional local_accessor correctly
+// compiles and runs.
+
+#include <iostream>
+#include <sycl/sycl.hpp>
+
+int main() {
+  size_t Result = 0;
+  sycl::queue Q;
+  {
+    sycl::buffer<size_t, 1> Buf(&Result, 1);
+    Q.submit([&](sycl::handler &CGH) {
+      sycl::local_accessor<size_t, 3> LocalMem(sycl::range<3>(1, 1, 1), CGH);
+      auto Acc = Buf.get_access(CGH);
+      CGH.parallel_for(1, [=](sycl::item<1> It) {
+        LocalMem[It][It][It] = 42;
+        Acc[It] = LocalMem[It][It][It];
+      });
+    });
+  }
+  assert(Result == 42);
+  std::cout << "success!" << std::endl;
+  return 0;
+}