Rereloop fuzz fix (#1259)

* fix relooper bug, ensure function body has right type, as relooper output does not flow stuff out, but wasm functions with a result do expect a flow value, so none is not an option. in other words, as the docs say, a relooper block must end with a terminator (return, unreachable, break, etc.) and not flow out.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/passes/ReReloop.cpp b/src/passes/ReReloop.cpp
index 99e60a72f..ff1eec6b5 100644
--- a/src/passes/ReReloop.cpp
+++ b/src/passes/ReReloop.cpp
@@ -345,6 +345,18 @@ struct ReReloop final : public Pass {
       auto temp = builder->addVar(function, i32);
       CFG::RelooperBuilder builder(*module, temp);
       function->body = relooper.Render(builder);
+      // if the function has a result, and the relooper emitted
+      // something that seems like it flows out without a value
+      // (but that path is never reached; it just has a br to it
+      // because of the relooper's boilerplate switch-handling
+      // code, for example, which could be optimized out later
+      // but isn't yet), then make sure it has a proper type
+      if (function->result != none && function->body->type == none) {
+        function->body = builder.makeSequence(
+          function->body,
+          builder.makeUnreachable()
+        );
+      }
     }
     // TODO: should this be in the relooper itself?
     ReFinalize().walk(function->body);