[wasm-metadce] Add support for tags (#4250)

This adds support for tag-using instructions (`throw` and `catch`) to
wasm-metadce. We had to use a hacky workaround in
emscripten-core/emscripten#15266 because of the lack of this support;
after this lands we can remove it.

1 files changed, 17 insertions, 0 deletions

diff --git a/src/tools/wasm-metadce.cpp b/src/tools/wasm-metadce.cpp
index 23a2d0fcc..00fa87ce2 100644
--- a/src/tools/wasm-metadce.cpp
+++ b/src/tools/wasm-metadce.cpp
@@ -263,6 +263,12 @@ struct MetaDCEGraph {
       }
       void visitGlobalGet(GlobalGet* curr) { handleGlobal(curr->name); }
       void visitGlobalSet(GlobalSet* curr) { handleGlobal(curr->name); }
+      void visitThrow(Throw* curr) { handleTag(curr->tag); }
+      void visitTry(Try* curr) {
+        for (auto tag : curr->catchTags) {
+          handleTag(tag);
+        }
+      }
 
     private:
       MetaDCEGraph* parent;
@@ -282,6 +288,17 @@ struct MetaDCEGraph {
         parent->nodes[parent->functionToDCENode[getFunction()->name]]
           .reaches.push_back(dceName);
       }
+
+      void handleTag(Name name) {
+        Name dceName;
+        if (!getModule()->getTag(name)->imported()) {
+          dceName = parent->tagToDCENode[name];
+        } else {
+          dceName = parent->importIdToDCENode[parent->getTagImportId(name)];
+        }
+        parent->nodes[parent->functionToDCENode[getFunction()->name]]
+          .reaches.push_back(dceName);
+      }
     };
 
     PassRunner runner(&wasm);