NoExitRuntime pass: Don't assume arguments have no side effects (#2953)

This bug was present from the very first version of this pass from 2018,
but it went unnoticed until now when a large project broke on it, for
some reason after

emscripten-core/emscripten#11403

Nothing wrong in that PR, probably just luck that it started to happen
there...

1 files changed, 11 insertions, 1 deletions

diff --git a/src/passes/NoExitRuntime.cpp b/src/passes/NoExitRuntime.cpp
index 82a296cfc..deffccd36 100644
--- a/src/passes/NoExitRuntime.cpp
+++ b/src/passes/NoExitRuntime.cpp
@@ -46,7 +46,17 @@ struct NoExitRuntime : public WalkerPass<PostWalker<NoExitRuntime>> {
     }
     for (auto name : ATEXIT_NAMES) {
       if (name == import->base) {
-        replaceCurrent(Builder(*getModule()).replaceWithIdenticalType(curr));
+        // Remove the call, and drop the arguments (which may have side
+        // effects); let other passes clean that up more.
+        Builder builder(*getModule());
+        std::vector<Expression*> args;
+        for (auto* operand : curr->operands) {
+          args.push_back(builder.makeDrop(operand));
+        }
+        // Ensure the block has the right type using the last arg.
+        args.push_back(builder.replaceWithIdenticalType(curr));
+        replaceCurrent(builder.makeBlock(args));
+        break;
       }
     }
   }