[wasm] Get rid of extra wrappers when import another wasm export

src/runtime/runtime-test.cc

Index: src/runtime/runtime-test.cc
diff --git a/src/runtime/runtime-test.cc b/src/runtime/runtime-test.cc
index 2232b190599a2b1a3025ea72bb44ef23596130ce..6fff4cffe18340873dfe2e3d26d5b4f6944f51fd 100644
--- a/src/runtime/runtime-test.cc
+++ b/src/runtime/runtime-test.cc
@@ -282,6 +282,75 @@ RUNTIME_FUNCTION(Runtime_ClearFunctionTypeFeedback) {
   return isolate->heap()->undefined_value();
 }
 
+RUNTIME_FUNCTION(Runtime_CheckWasmWrapperElision) {
+  // This only supports the case where the function being exported
+  // calls exactly one import
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 2);
+  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
+  // If type is 0, it means that it is supposed to be a direct call to WASM
+  // function
+  // If type is 1, it means that it is supposed to have wrappers
+  CONVERT_ARG_HANDLE_CHECKED(Smi, type, 1);
+  Handle<Code> export_code = handle(function->code());
+  if (export_code->kind() != Code::JS_TO_WASM_FUNCTION) {

[Mircea Trofin, 2016/08/04 18:21:08]

actually, this is a fine place to fail (CHECK). The contract of the
CheckWasmWrapperElision function is that the caller must pass in a module
export. If that's invalidated, it's a bug in the caller's code, and failfast is
fine.

[Chen, 2016/08/04 20:05:07]

Done.

+    return isolate->heap()->ToBoolean(false);
+  }
+  int const mask = RelocInfo::ModeMask(RelocInfo::CODE_TARGET);
+  // check the type of the $export_fct
+  Handle<Code> export_fct;
+  int count = 0;
+  for (RelocIterator it(*export_code, mask); !it.done(); it.next()) {
+    RelocInfo* rinfo = it.rinfo();
+    Address target_address = rinfo->target_address();
+    Code* target = Code::GetCodeFromTargetAddress(target_address);
+    if (target->kind() == Code::WASM_FUNCTION) {
+      ++count;
+      export_fct = handle(target);
+    }
+  }
+  if (count != 1) {

[Mircea Trofin, 2016/08/04 18:21:08]

This is also a CHECK - an export is expected to wrap a wasm function.

[Chen, 2016/08/04 20:05:07]

Done.

+    return isolate->heap()->ToBoolean(false);
+  }
+  // check the type of the $increment

[Mircea Trofin, 2016/08/04 18:21:08]

$increment?

[Chen, 2016/08/04 20:05:07]

Done.

+  Handle<Code> wrapped_fct;
+  count = 0;
+  for (RelocIterator it(*export_fct, mask); !it.done(); it.next()) {
+    RelocInfo* rinfo = it.rinfo();
+    Address target_address = rinfo->target_address();
+    Code* target = Code::GetCodeFromTargetAddress(target_address);
+    if (target->kind() == Code::WASM_FUNCTION) {
+      ++count;
+      wrapped_fct = handle(target);
+    }
+  }
+  if (count != 1) {

[Mircea Trofin, 2016/08/04 18:21:08]

also a CHECK

[Chen, 2016/08/04 20:05:07]

Done.

+    return isolate->heap()->ToBoolean(false);
+  }
+  // check the type of the imported exported function, it should be also a WASM
+  // function in our case
+  Handle<Code> imported_fct;
+  Code::Kind target_kind;
+  if (type->value() == 0) {
+    target_kind = Code::WASM_FUNCTION;
+  } else if (type->value() == 1) {
+    target_kind = Code::WASM_TO_JS_FUNCTION;
+  }
+  count = 0;
+  for (RelocIterator it(*wrapped_fct, mask); !it.done(); it.next()) {
+    RelocInfo* rinfo = it.rinfo();
+    Address target_address = rinfo->target_address();
+    Code* target = Code::GetCodeFromTargetAddress(target_address);
+    if (target->kind() == target_kind) {
+      ++count;
+      imported_fct = handle(target);
+    }
+  }

[Mircea Trofin, 2016/08/04 18:21:08]

CHECK_LE(count, 1)

[Chen, 2016/08/04 20:05:07]

Done.

+  if (count != 1) {
+    return isolate->heap()->ToBoolean(false);
+  }
+  return isolate->heap()->ToBoolean(true);
+}
 
 RUNTIME_FUNCTION(Runtime_NotifyContextDisposed) {
   HandleScope scope(isolate);