Index: External/CUDA/CMakeLists.txt
===================================================================
--- External/CUDA/CMakeLists.txt
+++ External/CUDA/CMakeLists.txt
@@ -110,6 +110,7 @@
   # buildbot a lot.
   create_one_local_test_f(simd simd.cu
                           "cuda-(8[.]0|9[.]2)-c[+][+]11-libc[+][+]")
+  create_one_local_test(test_round test_round.cu)
 endmacro()
 
 macro(thrust_make_test_name TestName TestSourcePath)
Index: External/CUDA/test_round.cu
===================================================================
--- /dev/null
+++ External/CUDA/test_round.cu
@@ -0,0 +1,54 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <iostream>
+#include <cassert>
+
+// Test the implementation of llvm intrinsic round. In particular, when the
+// source is equidistant between two integers, it rounds away from zero.
+//
+// In CUDA libdevice, the implementation of round separates the values into
+// three regions and uses a region specific rounding method to calculate
+// the result:
+//    abs(x) <= 0.5
+//    2 ^ 23 > abs(x) > 0.5 (float)
+//    abs(x) >= 2 ^ 23 (float)
+//    For double, 2 ^ 23 above is replaced with 2 ^ 52
+//
+// The PTX backend implements round in a similar way. We chose the test values
+// based on this.
+
+__global__ void test_round(float v) {
+  assert(__builtin_roundf(-0.5f + v) == -1.0f);
+  assert(__builtin_roundf(8.5f + v) == 9.0f);
+  assert(__builtin_roundf(-8.38861e+06f + v) == -8.38861e+06f);
+  assert(__builtin_roundf(8.38861e+06f + v) == 8.38861e+06f);
+
+  assert(__builtin_round(0.5 + v) == 1.0f);
+  assert(__builtin_round(-8.5 + v) == -9.0f);
+  assert(__builtin_round(4.5035996e+15 + v) == 4.5035996e+15);
+  assert(__builtin_round(-4.5035996e+15 + v) == -4.5035996e+15);
+  // test values beyond +/- max(float)
+  assert(__builtin_round(3.4e39 + v) == 3.4e39);
+  assert(__builtin_round(-3.4e39 + v) == -3.4e39);
+}
+
+int main(int argc, char* argv[]) {
+  float host_value = 0;
+
+  // Launch the kernel.
+  test_round<<<1, 1>>>(0);
+  cudaError_t err = cudaDeviceSynchronize();
+  if (err != cudaSuccess) {
+    printf("CUDA error %d\n", (int)err);
+    return 1;
+  }
+
+  printf("Success!\n");
+  return 0;
+}