Add AutoDrop support for Try (#2663)

This adds AutoDrop (+ ReFinalize) support for Try. We don't have
`--autodrop` option so I can't add a separate test for this, but this is
basically the same as what If does.

2 files changed, 17 insertions, 0 deletions

diff --git a/src/ir/ReFinalize.cpp b/src/ir/ReFinalize.cpp
index 422f462c0..6d20d6597 100644
--- a/src/ir/ReFinalize.cpp
+++ b/src/ir/ReFinalize.cpp
@@ -128,6 +128,9 @@ void ReFinalize::visitThrow(Throw* curr) { curr->finalize(); }
 void ReFinalize::visitRethrow(Rethrow* curr) { curr->finalize(); }
 void ReFinalize::visitBrOnExn(BrOnExn* curr) {
   curr->finalize();
+  if (curr->exnref->type == Type::unreachable) {
+    replaceUntaken(curr->exnref, nullptr);
+  }
   updateBreakValueType(curr->name, curr->sent);
 }
 void ReFinalize::visitNop(Nop* curr) { curr->finalize(); }
diff --git a/src/ir/utils.h b/src/ir/utils.h
index b7c5b9cba..7362cbe1a 100644
--- a/src/ir/utils.h
+++ b/src/ir/utils.h
@@ -301,6 +301,20 @@ struct AutoDrop : public WalkerPass<ExpressionStackWalker<AutoDrop>> {
     }
   }
 
+  void visitTry(Try* curr) {
+    bool acted = false;
+    if (maybeDrop(curr->body)) {
+      acted = true;
+    }
+    if (maybeDrop(curr->catchBody)) {
+      acted = true;
+    }
+    if (acted) {
+      reFinalize();
+      assert(curr->type == Type::none);
+    }
+  }
+
   void doWalkFunction(Function* curr) {
     ReFinalize().walkFunctionInModule(curr, getModule());
     walk(curr->body);