Preserve Function HeapTypes (#3952)

When using nominal types, func.ref of two functions with identical signatures
but different HeapTypes will yield different types. To preserve these semantics,
Functions need to track their HeapTypes, not just their Signatures.

This PR replaces the Signature field in Function with a HeapType field and adds
new utility methods to make it almost as simple to update and query the function
HeapType as it was to update and query the Function Signature.

1 files changed, 2 insertions, 4 deletions

diff --git a/src/passes/StackCheck.cpp b/src/passes/StackCheck.cpp
index 23fd5be3d..e7fc3c6b3 100644
--- a/src/passes/StackCheck.cpp
+++ b/src/passes/StackCheck.cpp
@@ -39,12 +39,10 @@ static void importStackOverflowHandler(Module& module, Name name) {
   ImportInfo info(module);
 
   if (!info.getImportedFunction(ENV, name)) {
-    auto* import = new Function;
-    import->name = name;
+    auto import = Builder::makeFunction(name, Signature(), {});
     import->module = ENV;
     import->base = name;
-    import->sig = Signature(Type::none, Type::none);
-    module.addFunction(import);
+    module.addFunction(std::move(import));
   }
 }