Avoid host allocations for by-offload arguments to GPU kernels

Signed-off-by: Engin Kayraklioglu <e-kayrakli@users.noreply.github.com>

runtime/src/chpl-gpu.c

@@ -411,14 +411,19 @@ static void cfg_add_offload_param(kernel_cfg* cfg, void* arg, size_t size) {
 
   cfg->param_dyn_allocated[i] = true;
 
+  // the kernel_params array must store the addresses of things that will be
+  // copied to the device memory before the kernel launch. For by-offload
+  // params, we need it to store the address of the pointer generated by
+  // chpl_gpu_mem_array_alloc. We need to allocate dynamic memory for that
+  // address-to-pointer as well, because otherwise the address (which is just
+  // another void*) will go out of scope at the end of this function.
   cfg->kernel_params[i] = chpl_mem_alloc(sizeof(void*),
                                          CHPL_RT_MD_GPU_KERNEL_PARAM, cfg->ln,
                                          cfg->fn);
 
-  // TODO this doesn't work on EX, why?
-  // *kernel_params[i] = chpl_gpu_impl_mem_array_alloc(cur_arg_size, stream);
-  *(cfg->kernel_params[i]) = chpl_gpu_mem_alloc(size, CHPL_RT_MD_GPU_KERNEL_ARG,
-                                                cfg->ln, cfg->fn);
+  *(cfg->kernel_params[i]) = chpl_gpu_mem_array_alloc(size,
+                                                      CHPL_RT_MD_GPU_KERNEL_ARG,
+                                                      cfg->ln, cfg->fn);
 
   chpl_gpu_impl_copy_host_to_device(*(cfg->kernel_params[i]), arg, size,
                                     cfg->stream);