Make local.tee's type its local's type (#2511)

According to the current spec, `local.tee`'s return type should be the
same as its local's type. (Discussions on whether we should change this
rule is going on in WebAssembly/reference-types#55, but here I will
assume this spec does not change. If this changes, we should change many
parts of Binaryen transformation anyway...)

But currently in Binaryen `local.tee`'s type is computed from its
value's type. This didn't make any difference in the MVP, but after we
have subtype relationship in #2451, this can become a problem. For
example:
```
(func $test (result funcref) (local $0 anyref)
  (local.tee $0
    (ref.func $test)
  )
)
```
This shouldn't validate in the spec, but this will pass Binaryen
validation with the current `local.tee` implementation.

This makes `local.tee`'s type computed from the local's type, and makes
`LocalSet::makeTee` get a type parameter, to which we should pass the
its corresponding local's type. We don't embed the local type in the
class `LocalSet` because it may increase memory size.

This also fixes the type of `local.get` to be the local type where
`local.get` and `local.set` pair is created from `local.tee`.

1 files changed, 4 insertions, 3 deletions

diff --git a/src/passes/Untee.cpp b/src/passes/Untee.cpp
index 79c76b988..6e5fb489b 100644
--- a/src/passes/Untee.cpp
+++ b/src/passes/Untee.cpp
@@ -41,9 +41,10 @@ struct Untee : public WalkerPass<PostWalker<Untee>> {
       } else {
         // a normal tee. replace with set and get
         Builder builder(*getModule());
-        replaceCurrent(builder.makeSequence(
-          curr, builder.makeLocalGet(curr->index, curr->value->type)));
-        curr->setTee(false);
+        LocalGet* get = builder.makeLocalGet(
+          curr->index, getFunction()->getLocalType(curr->index));
+        replaceCurrent(builder.makeSequence(curr, get));
+        curr->makeSet();
       }
     }
   }