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, 1 insertions, 2 deletions

diff --git a/src/ir/hashed.h b/src/ir/hashed.h
index fe959936a..4a6e1647e 100644
--- a/src/ir/hashed.h
+++ b/src/ir/hashed.h
@@ -64,8 +64,7 @@ struct FunctionHasher : public WalkerPass<PostWalker<FunctionHasher>> {
   void doWalkFunction(Function* func) { output->at(func) = hashFunction(func); }
 
   static size_t hashFunction(Function* func) {
-    auto digest = hash(func->sig.params.getID());
-    rehash(digest, func->sig.results.getID());
+    auto digest = hash(func->type);
     for (auto type : func->vars) {
       rehash(digest, type.getID());
     }