[SYCL][CUDA] Add missing barrier to collectives

libclc/ptx-nvidiacl/libspirv/group/collectives.cl

@@ -264,6 +264,7 @@ __CLC_SUBGROUP_COLLECTIVE(FMax, __CLC_MAX, double, -DBL_MAX)
         result = OP(sg_x, scratch[sg_id - 1]);                                 \
       }                                                                        \
     }                                                                          \
+    __spirv_ControlBarrier(Workgroup, 0, 0);                                   \
     return result;                                                             \
   }
 

sycl/test/on-device/back_to_back_collectives.cpp

@@ -0,0 +1,64 @@
+// RUN: %clangxx -fsycl -fsycl-targets=%sycl_triple %s -o %t.out
+// RUN: %HOST_RUN_PLACEHOLDER %t.out
+// RUN: %CPU_RUN_PLACEHOLDER %t.out
+// RUN: %GPU_RUN_PLACEHOLDER %t.out
+// RUN: %ACC_RUN_PLACEHOLDER %t.out
+
+#include <CL/sycl.hpp>
+#include <numeric>
+#include <vector>
+using namespace cl::sycl;
+using namespace cl::sycl::ONEAPI;
+
+int main() {
+  queue q;
+  if (q.get_device().is_host()) {
+    std::cout << "Skipping test\n";
+    return 0;
+  }
+
+  // Use max work-group size to maximize chance of race
+  int N = q.get_device().get_info<info::device::max_work_group_size>();
+
+  std::vector<int> Input(N), Sum(N), EScan(N), IScan(N);
+  std::iota(Input.begin(), Input.end(), 0);
+  std::fill(Sum.begin(), Sum.end(), 0);
+  std::fill(EScan.begin(), EScan.end(), 0);
+  std::fill(IScan.begin(), IScan.end(), 0);
+
+  {
+    buffer<int> InputBuf(Input.data(), N);
+    buffer<int> SumBuf(Sum.data(), N);
+    buffer<int> EScanBuf(EScan.data(), N);
+    buffer<int> IScanBuf(IScan.data(), N);
+    q.submit([&](handler &h) {
+      auto Input = InputBuf.get_access<access::mode::read>(h);
+      auto Sum = SumBuf.get_access<access::mode::write>(h);
+      auto EScan = EScanBuf.get_access<access::mode::write>(h);
+      auto IScan = IScanBuf.get_access<access::mode::write>(h);
+      h.parallel_for(nd_range<1>(N, N), [=](nd_item<1> it) {
+        size_t i = it.get_global_id(0);
+        auto g = it.get_group();
+        // Loop to increase number of back-to-back calls
+        for (int r = 0; r < 10; ++r) {
+          Sum[i] = reduce(g, Input[i], plus<>());
+          EScan[i] = exclusive_scan(g, Input[i], plus<>());
+          IScan[i] = inclusive_scan(g, Input[i], plus<>());
+        }
+      });
+    });
+  }
+
+  int sum = 0;
+  bool passed = true;
+  for (int i = 0; i < N; ++i) {
+    passed &= (sum == EScan[i]);
+    sum += i;
+    passed &= (sum == IScan[i]);
+  }
+  for (int i = 0; i < N; ++i) {
+    passed &= (sum == Sum[i]);
+  }
+  std::cout << "Test passed." << std::endl;
+  return 0;
+}