Refactor TypeUpdating non-nullability code. NFC (#4063)

This moves code out of the existing methods so that it can be
called directly from more places. A later PR will use the new
methods.

2 files changed, 29 insertions, 10 deletions

diff --git a/src/ir/type-updating.cpp b/src/ir/type-updating.cpp
index d91c5f385..a3ce8aad7 100644
--- a/src/ir/type-updating.cpp
+++ b/src/ir/type-updating.cpp
@@ -51,13 +51,7 @@ void handleNonDefaultableLocals(Function* func, Module& wasm) {
       // We do not need to process params, which can legally be non-nullable.
       continue;
     }
-    auto type = func->getLocalType(get->index);
-    if (type.isNonNullable()) {
-      // The get should now return a nullable value, and a ref.as_non_null
-      // fixes that up.
-      get->type = Type(type.getHeapType(), Nullable);
-      *getp = builder.makeRefAs(RefAsNonNull, get);
-    }
+    *getp = fixLocalGet(get, wasm);
   }
 
   // Update tees, whose type must match the local (if the wasm spec changes for
@@ -83,10 +77,26 @@ void handleNonDefaultableLocals(Function* func, Module& wasm) {
   // Rewrite the types of the function's vars (which we can do now, after we
   // are done using them to know which local.gets etc to fix).
   for (auto& type : func->vars) {
-    if (type.isNonNullable()) {
-      type = Type(type.getHeapType(), Nullable);
-    }
+    type = getValidLocalType(type, wasm.features);
+  }
+}
+
+Type getValidLocalType(Type type, FeatureSet features) {
+  assert(canHandleAsLocal(type));
+  if (type.isNonNullable() && !features.hasGCNNLocals()) {
+    type = Type(type.getHeapType(), Nullable);
+  }
+  return type;
+}
+
+Expression* fixLocalGet(LocalGet* get, Module& wasm) {
+  if (get->type.isNonNullable() && !wasm.features.hasGCNNLocals()) {
+    // The get should now return a nullable value, and a ref.as_non_null
+    // fixes that up.
+    get->type = getValidLocalType(get->type, wasm.features);
+    return Builder(wasm).makeRefAs(RefAsNonNull, get);
   }
+  return get;
 }
 
 } // namespace TypeUpdating
diff --git a/src/ir/type-updating.h b/src/ir/type-updating.h
index c9e4f4f0b..4668c0ad5 100644
--- a/src/ir/type-updating.h
+++ b/src/ir/type-updating.h
@@ -317,6 +317,15 @@ bool canHandleAsLocal(Type type);
 // This may also handle other types of nondefaultable locals in the future.
 void handleNonDefaultableLocals(Function* func, Module& wasm);
 
+// Returns the type that a local should be, after handling of non-
+// defaultability.
+Type getValidLocalType(Type type, FeatureSet features);
+
+// Given a local.get, returns a proper replacement for it, taking into account
+// the extra work we need to do to handle non-defaultable values (e.g., add a
+// ref.as_non_null around it, if the local should be non-nullable but is not).
+Expression* fixLocalGet(LocalGet* get, Module& wasm);
+
 } // namespace TypeUpdating
 
 } // namespace wasm