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, 1 deletions

diff --git a/src/passes/DuplicateImportElimination.cpp b/src/passes/DuplicateImportElimination.cpp
index b917c5fe8..a4d9065c5 100644
--- a/src/passes/DuplicateImportElimination.cpp
+++ b/src/passes/DuplicateImportElimination.cpp
@@ -41,7 +41,7 @@ struct DuplicateImportElimination : public Pass {
         auto previousFunc = module->getFunction(previousName);
         // It is ok to import the same thing with multiple types; we can only
         // merge if the types match, of course.
-        if (previousFunc->sig == func->sig) {
+        if (previousFunc->type == func->type) {
           replacements[func->name] = previousName;
           toRemove.push_back(func->name);
           continue;