Add sliceSum gpu using cub/hipcub

tests/core/Test_sliceSum.cc

@@ -0,0 +1,56 @@
+#include <Grid/Grid.h>
+
+
+int main (int argc, char ** argv) {
+    
+    using namespace Grid;
+
+    Grid_init(&argc,&argv);
+
+
+    Coordinate latt_size({64,64,64,16});
+    auto simd_layout = GridDefaultSimd(Nd, vComplexD::Nsimd());
+    auto mpi_layout = GridDefaultMpi();
+    GridCartesian Grid(latt_size, simd_layout, mpi_layout);
+
+    std::vector<int> seeds({1, 2, 3, 4});
+
+    GridParallelRNG pRNG(&Grid);
+    pRNG.SeedFixedIntegers(seeds);
+
+    LatticeComplexD test_data(&Grid);
+    gaussian(pRNG,test_data);
+
+    std::vector<TComplexD> reduction_reference;
+    std::vector<TComplexD> reduction_result;
+
+    //warmup
+    for (int sweeps = 0; sweeps < 5; sweeps++) {
+      sliceSumGpu(test_data,reduction_result,0);
+    }
+
+
+    for (int i = 0; i < Nd; i++) {
+        RealD t=-usecond();
+        sliceSum(test_data,reduction_reference,i);
+        t+=usecond();
+        std::cout << " sliceSum took "<<t<<" usecs"<<std::endl;
+        
+        RealD tgpu=-usecond();
+        tracePush("sliceSumGpu");
+        sliceSumGpu(test_data,reduction_result,i);
+        tracePop("sliceSumGpu");
+        tgpu+=usecond();
+        std::cout <<" sliceSumGpu took "<<tgpu<<" usecs"<<std::endl;
+
+    for(int t=0;t<reduction_reference.size();t++){
+
+      auto diff = reduction_reference[t]-reduction_result[t];
+      assert(abs(TensorRemove(diff)) < 1e-8 );
+    }
+
+    
+    }
+    Grid_finalize();
+    return 0;
+}