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, 5 insertions, 4 deletions

diff --git a/src/binaryen-c.cpp b/src/binaryen-c.cpp
index 35f394fd1..70712d4d4 100644
--- a/src/binaryen-c.cpp
+++ b/src/binaryen-c.cpp
@@ -1197,22 +1197,23 @@ BinaryenExpressionRef BinaryenLocalSet(BinaryenModuleRef module,
 
   ret->index = index;
   ret->value = (Expression*)value;
-  ret->setTee(false);
+  ret->makeSet();
   ret->finalize();
   return static_cast<Expression*>(ret);
 }
 BinaryenExpressionRef BinaryenLocalTee(BinaryenModuleRef module,
                                        BinaryenIndex index,
-                                       BinaryenExpressionRef value) {
+                                       BinaryenExpressionRef value,
+                                       BinaryenType type) {
   auto* ret = ((Module*)module)->allocator.alloc<LocalSet>();
 
   if (tracing) {
-    traceExpression(ret, "BinaryenLocalTee", index, value);
+    traceExpression(ret, "BinaryenLocalTee", index, value, type);
   }
 
   ret->index = index;
   ret->value = (Expression*)value;
-  ret->setTee(true);
+  ret->makeTee(Type(type));
   ret->finalize();
   return static_cast<Expression*>(ret);
 }