allow all three backends to co-exist in a single build (#270)

* add support for compiling all backends

also include the logic to select backends either based on user requests
or through some heuristics

* checkpoint for compiling all backends

* final checkpoint

all tests seem to pass when compiling all three backends simultaneasly
and forcing to use any of the three Backends.

* update PR to new envvar system

src/backend_bc.cpp

@@ -29,9 +29,11 @@
 
 #if defined(USE_GDA)
 #include "gda/backend_gda.hpp"
-#elif defined(USE_RO)
+#endif
+#if defined(USE_RO)
 #include "reverse_offload/backend_ro.hpp"
-#elif defined(USE_IPC)
+#endif
+#if defined(USE_IPC)
 #include "ipc/backend_ipc.hpp"
 #endif
 
@@ -250,7 +252,20 @@ void Backend::reset_stats() {
 }
 
 __device__ bool Backend::create_ctx(int64_t option, rocshmem_ctx_t* ctx) {
-#if defined(USE_GDA)
+#if defined(USE_GDA) && defined(USE_RO) && defined(USE_IPC)
+  switch(this->type) {
+  case BackendType::GDA_BACKEND:
+    return static_cast<GDABackend*>(this)->create_ctx(option, ctx);
+    break;
+  case BackendType::RO_BACKEND:
+    return static_cast<ROBackend*>(this)->create_ctx(option, ctx);
+    break;
+  case BackendType::IPC_BACKEND:
+  default:
+      return static_cast<IPCBackend*>(this)->create_ctx(option, ctx);
+      break;
+  }
+#elif defined(USE_GDA)
   return static_cast<GDABackend*>(this)->create_ctx(option, ctx);
 #elif defined(USE_RO)
   return static_cast<ROBackend*>(this)->create_ctx(option, ctx);
@@ -260,7 +275,20 @@ __device__ bool Backend::create_ctx(int64_t option, rocshmem_ctx_t* ctx) {
 }
 
 __device__ void Backend::destroy_ctx(rocshmem_ctx_t* ctx) {
-#if defined(USE_GDA)
+#if defined(USE_GDA) && defined(USE_RO) && defined(USE_IPC)
+  switch(this->type) {
+  case BackendType::GDA_BACKEND:
+    static_cast<GDABackend*>(this)->destroy_ctx(ctx);
+    break;
+  case BackendType::RO_BACKEND:
+    static_cast<ROBackend*>(this)->destroy_ctx(ctx);
+    break;
+  case BackendType::IPC_BACKEND:
+  default:
+    static_cast<IPCBackend*>(this)->destroy_ctx(ctx);
+    break;
+  }
+#elif defined(USE_GDA)
   static_cast<GDABackend*>(this)->destroy_ctx(ctx);
 #elif defined(USE_RO)
   static_cast<ROBackend*>(this)->destroy_ctx(ctx);