Handle workspace reservation when workspace size is zero (#1797)

* return nullptr when workspace size is zero+modify insert method to accept const lvalue ref

* Unit test added

src/ngraph/runtime/gpu/gpu_memory_manager.cpp

@@ -152,6 +152,11 @@ size_t runtime::gpu::GPUAllocator::reserve_argspace(const void* data, size_t siz
 
 size_t runtime::gpu::GPUAllocator::reserve_workspace(size_t size, bool zero_initialize)
 {
+    if (size == 0)
+    {
+        return m_manager->m_primitive_emitter->insert([]() { return nullptr; });
+    }
+
     size_t offset = m_manager->m_workspace_manager->allocate(size);
     m_active.push(offset);
     auto local = std::prev(m_manager->m_workspace_mem.end());
@@ -171,7 +176,7 @@ size_t runtime::gpu::GPUAllocator::reserve_workspace(size_t size, bool zero_init
         }
         return workspace_ptr;
     };
-    return m_manager->m_primitive_emitter->insert(mem_primitive);
+    return m_manager->m_primitive_emitter->insert(std::move(mem_primitive));
 }
 
 void runtime::gpu::GPUAllocator::close()

src/ngraph/runtime/gpu/gpu_primitive_emitter.cpp

@@ -59,7 +59,7 @@ size_t GPUPrimitiveEmitter::insert(std::unique_ptr<gpu::primitive>&& f)
     m_gpu_primitives.push_back(m_managed_primitives.back().get());
     return m_gpu_primitives.size() - 1;
 }
-size_t GPUPrimitiveEmitter::insert(gpu::memory_primitive& f)
+size_t GPUPrimitiveEmitter::insert(const gpu::memory_primitive& f)
 {
     m_gpu_mem_primitives.push_back(f);
     return m_gpu_mem_primitives.size() - 1;

src/ngraph/runtime/gpu/gpu_primitive_emitter.hpp

@@ -43,7 +43,7 @@ namespace ngraph
                     return m_gpu_mem_primitives;
                 }
                 size_t insert(std::unique_ptr<gpu::primitive>&& f);
-                size_t insert(gpu::memory_primitive& f);
+                size_t insert(const gpu::memory_primitive& f);
                 size_t lookup(std::string hash);
                 void cache(const std::string& hash, const size_t& index);
                 GPUAllocator get_memory_allocator() { return m_memory_manager.build_allocator(); }

test/gpu_test.cpp

@@ -40,6 +40,20 @@ TEST(gpu_test, memory_manager_unallocated)
     ASSERT_ANY_THROW(mem_primitive());
 }
 
+TEST(gpu_test, memory_manager_zero_workspace)
+{
+    runtime::gpu::GPUPrimitiveEmitter emitter;
+    size_t idx_null, idx_not_null;
+    {
+        auto allocator = emitter.get_memory_allocator();
+        idx_null = allocator.reserve_workspace(0);
+        idx_not_null = allocator.reserve_workspace(10);
+    }
+    emitter.allocate_primitive_memory();
+    EXPECT_EQ(emitter.get_memory_primitives()[idx_null](), nullptr);
+    EXPECT_NE(emitter.get_memory_primitives()[idx_not_null](), nullptr);
+}
+
 TEST(gpu_test, memory_manager_allocated)
 {
     runtime::gpu::GPUPrimitiveEmitter emitter;