avoid trying to optimize ifs with unreachable conditions in remove-unused-brs, as they are dead code anyhow, and it is pointless to work hard to handle the type changes

2 files changed, 19 insertions, 4 deletions

diff --git a/src/passes/RemoveUnusedBrs.cpp b/src/passes/RemoveUnusedBrs.cpp
index d2b7c944f..a3ef15639 100644
--- a/src/passes/RemoveUnusedBrs.cpp
+++ b/src/passes/RemoveUnusedBrs.cpp
@@ -82,6 +82,10 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
       self->valueCanFlow = true; // start optimistic
     } else if (curr->is<If>()) {
       auto* iff = curr->cast<If>();
+      if (iff->condition->type == unreachable) {
+        // avoid trying to optimize this, we never reach it anyhow
+        return;
+      }
       if (iff->ifFalse) {
         assert(self->ifStack.size() > 0);
         for (auto* flow : self->ifStack.back()) {
@@ -174,8 +178,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
 
     if (iff) {
       if (iff->condition->type == unreachable) {
-        // avoid all the branching, we never reach it anyhow
-        *currp = iff->condition;
+        // avoid trying to optimize this, we never reach it anyhow
         return;
       }
       self->pushTask(doVisitIf, currp);
diff --git a/test/passes/remove-unused-brs.txt b/test/passes/remove-unused-brs.txt
index 599459c57..c4c2710d3 100644
--- a/test/passes/remove-unused-brs.txt
+++ b/test/passes/remove-unused-brs.txt
@@ -1062,13 +1062,25 @@
  )
  (func $unreachable-if-that-could-be-a-br_if (type $7) (result i64)
   (loop $label$3
-   (unreachable)
+   (if
+    (unreachable)
+    (f64.const 1)
+    (br $label$3)
+   )
    (i64.const 1)
   )
  )
  (func $nop-br-might-update-type (type $1)
   (block $label$39
-   (unreachable)
+   (if
+    (unreachable)
+    (if (result i32)
+     (i32.const 1)
+     (br $label$39)
+     (i32.const 0)
+    )
+    (i32.const 0)
+   )
   )
  )
 )