From 02277fb28f3a0632819b1046fddd0ec3de52a8a3 Mon Sep 17 00:00:00 2001
From: Alon Zakai <azakai@google.com>
Date: Wed, 5 Apr 2023 12:25:01 -0700
Subject: Wasm GC] Handle unreachability in a select child in trapOnNull()
 (#5630)

---
 src/passes/OptimizeInstructions.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

(limited to 'src')

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index c9e1ced19..f5a0c6756 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -1632,7 +1632,12 @@ struct OptimizeInstructions
       }
 
       if (auto* select = ref->dynCast<Select>()) {
-        if (select->ifTrue->type.isNull()) {
+        // We must check for unreachability explicitly here because a full
+        // refinalize only happens at the end. That is, the select may stil be
+        // reachable after we turned one child into an unreachable, and we are
+        // calling getResultOfFirst which will error on unreachability.
+        if (select->ifTrue->type.isNull() &&
+            select->ifFalse->type != Type::unreachable) {
           ref = builder.makeSequence(
             builder.makeDrop(select->ifTrue),
             getResultOfFirst(select->ifFalse,
-- 
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