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, 3 insertions, 2 deletions

diff --git a/src/passes/Flatten.cpp b/src/passes/Flatten.cpp
index 6f698367f..74788afb5 100644
--- a/src/passes/Flatten.cpp
+++ b/src/passes/Flatten.cpp
@@ -172,9 +172,10 @@ struct Flatten
             replaceCurrent(set->value); // trivial, no set happens
           } else {
             // use a set in a prelude + a get
-            set->setTee(false);
+            set->makeSet();
             ourPreludes.push_back(set);
-            replaceCurrent(builder.makeLocalGet(set->index, set->value->type));
+            Type localType = getFunction()->getLocalType(set->index);
+            replaceCurrent(builder.makeLocalGet(set->index, localType));
           }
         }
       } else if (auto* br = curr->dynCast<Break>()) {