[WASM] Update support for latest emcc, add ffi test.

python/tvm/contrib/emcc.py

@@ -42,6 +42,7 @@ def create_tvmjs_wasm(output, objects, options=None, cc="emcc"):
     cmd += ["-O3"]
 
     cmd += ["-std=c++14"]
+    cmd += ["--no-entry"]
     cmd += ["-s", "ERROR_ON_UNDEFINED_SYMBOLS=0"]
     cmd += ["-s", "STANDALONE_WASM=1"]
     cmd += ["-s", "ALLOW_MEMORY_GROWTH=1"]

web/Makefile

@@ -26,8 +26,8 @@ all: dist/wasm/tvmjs_runtime.wasm dist/wasm/tvmjs_runtime.wasi.js
 
 EMCC = emcc
 
-EMCC_CFLAGS = $(INCLUDE_FLAGS) -O3 -std=c++14 -Wno-ignored-attributes \
-	-s ALLOW_MEMORY_GROWTH=1 -s STANDALONE_WASM=1 -s ERROR_ON_UNDEFINED_SYMBOLS=0
+EMCC_CFLAGS = $(INCLUDE_FLAGS) -O3 -std=c++14 -Wno-ignored-attributes --no-entry \
+	-s ALLOW_MEMORY_GROWTH=1 -s STANDALONE_WASM=1 -s ERROR_ON_UNDEFINED_SYMBOLS=0 
 
 EMCC_LDFLAGS = --pre-js emcc/preload.js
 

web/emcc/wasm_runtime.cc

@@ -75,5 +75,13 @@ TVM_REGISTER_GLOBAL("testing.wrap_callback").set_body([](TVMArgs args, TVMRetVal
   PackedFunc pf = args[0];
   *ret = runtime::TypedPackedFunc<void()>([pf]() { pf(); });
 });
+
+// internal function used for debug and testing purposes
+TVM_REGISTER_GLOBAL("testing.object_use_count").set_body([](TVMArgs args, TVMRetValue* ret) {
+  runtime::ObjectRef obj = args[0];
+  // substract the current one because we always copy
+  // and get another value.
+  *ret = (obj.use_count() - 1);
+});
 }  // namespace runtime
 }  // namespace tvm

web/tests/node/test_packed_func.js

@@ -109,3 +109,16 @@ test("RegisterGlobal", () => {
   let syslib = tvm.systemLib();
   syslib.dispose();
 });
+
+test("NDArrayCbArg", () => {
+  let use_count = tvm.getGlobalFunc("testing.object_use_count");
+
+  let fcheck = tvm.toPackedFunc(function (x) {
+    assert(use_count(x) == 2);
+    x.dispose();
+  });
+  let x = tvm.empty([2], "float32").copyFrom([1, 2]);
+  assert(use_count(x) == 1);
+  fcheck(x);
+  assert(use_count(x) == 1);
+});