autodrop if body if no else

2 files changed, 10 insertions, 0 deletions

diff --git a/src/ast_utils.h b/src/ast_utils.h
index f7a486332..5deaa6a2c 100644
--- a/src/ast_utils.h
+++ b/src/ast_utils.h
@@ -832,6 +832,13 @@ struct AutoDrop : public WalkerPass<ExpressionStackWalker<AutoDrop, Visitor<Auto
     curr->finalize(); // we may have changed our type
   }
 
+  void visitIf(If* curr) {
+    // if without else does not return a value, so the body must be dropped if it is concrete
+    if (!curr->ifFalse && isConcreteWasmType(curr->ifTrue->type)) {
+      curr->ifTrue = Builder(*getModule()).makeDrop(curr->ifTrue);
+    }
+  }
+
   void visitFunction(Function* curr) {
     if (curr->result == none && isConcreteWasmType(curr->body->type)) {
       curr->body = Builder(*getModule()).makeDrop(curr->body);
diff --git a/src/wasm-validator.h b/src/wasm-validator.h
index 58a30f9a3..e23221337 100644
--- a/src/wasm-validator.h
+++ b/src/wasm-validator.h
@@ -104,6 +104,9 @@ public:
 
   void visitIf(If *curr) {
     shouldBeTrue(curr->condition->type == unreachable || curr->condition->type == i32 || curr->condition->type == i64, curr, "if condition must be valid");
+    if (!curr->ifFalse) {
+      shouldBeFalse(isConcreteWasmType(curr->ifTrue->type), curr, "if without else must not return a value in body");
+    }
   }
 
   // override scan to add a pre and a post check task to all nodes