3 files changed, 66 insertions, 5 deletions

diff --git a/src/passes/RemoveUnusedBrs.cpp b/src/passes/RemoveUnusedBrs.cpp
index a3ef15639..e627ce138 100644
--- a/src/passes/RemoveUnusedBrs.cpp
+++ b/src/passes/RemoveUnusedBrs.cpp
@@ -74,7 +74,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
         flows.push_back(currp);
         self->valueCanFlow = true; // start optimistic
       } else {
-        self->valueCanFlow = false;
+        self->stopValueFlow();
       }
     } else if (curr->is<Return>()) {
       flows.clear();
@@ -84,6 +84,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
       auto* iff = curr->cast<If>();
       if (iff->condition->type == unreachable) {
         // avoid trying to optimize this, we never reach it anyhow
+        self->stopFlow();
         return;
       }
       if (iff->ifFalse) {
@@ -94,7 +95,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
         self->ifStack.pop_back();
       } else {
         // if without else stops the flow of values
-        self->valueCanFlow = false;
+        self->stopValueFlow();
       }
     } else if (curr->is<Block>()) {
       // any breaks flowing to here are unnecessary, as we get here anyhow
@@ -132,16 +133,31 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
       }
     } else if (curr->is<Nop>()) {
       // ignore (could be result of a previous cycle)
-      self->valueCanFlow = false;
+      self->stopValueFlow();
     } else if (curr->is<Loop>()) {
       // do nothing - it's ok for values to flow out
     } else {
       // anything else stops the flow
-      flows.clear();
-      self->valueCanFlow = false;
+      self->stopFlow();
     }
   }
 
+  void stopFlow() {
+    flows.clear();
+    valueCanFlow = false;
+  }
+
+  void stopValueFlow() {
+    flows.erase(std::remove_if(flows.begin(), flows.end(), [&](Expression** currp) {
+      auto* curr = *currp;
+      if (auto* ret = curr->dynCast<Return>()) {
+        return ret->value;
+      }
+      return curr->cast<Break>()->value;
+    }), flows.end());
+    valueCanFlow = false;
+  }
+
   static void clear(RemoveUnusedBrs* self, Expression** currp) {
     self->flows.clear();
   }
diff --git a/test/passes/remove-unused-brs.txt b/test/passes/remove-unused-brs.txt
index c4c2710d3..7951cf18f 100644
--- a/test/passes/remove-unused-brs.txt
+++ b/test/passes/remove-unused-brs.txt
@@ -7,6 +7,7 @@
  (type $5 (func (param f32 i32 f32 i32 i32 f64 f32) (result i32)))
  (type $6 (func (param i32) (result i64)))
  (type $7 (func (result i64)))
+ (type $8 (func (result f32)))
  (memory $0 256 256)
  (func $b0-yes (type $0) (param $i1 i32)
   (block $topmost
@@ -1083,4 +1084,25 @@
    )
   )
  )
+ (func $no-flow-through-if-without-else (type $8) (result f32)
+  (local $0 i32)
+  (local $2 f32)
+  (block $label$0 (result f32)
+   (if (result f32)
+    (get_local $0)
+    (block $label$11
+     (return
+      (f32.const 239)
+     )
+     (if
+      (i32.const 0)
+      (return
+       (get_local $2)
+      )
+     )
+    )
+    (f32.const -9223372036854775808)
+   )
+  )
+ )
 )
diff --git a/test/passes/remove-unused-brs.wast b/test/passes/remove-unused-brs.wast
index 32c4ece6a..20441d9e4 100644
--- a/test/passes/remove-unused-brs.wast
+++ b/test/passes/remove-unused-brs.wast
@@ -966,5 +966,28 @@
     )
    )
   )
+  (func $no-flow-through-if-without-else (result f32)
+   (local $0 i32)
+   (local $2 f32)
+   (block $label$0
+    (if
+     (get_local $0)
+     (block $label$11
+      (return
+       (f32.const 239)
+      )
+      (if
+       (i32.const 0)
+       (return
+        (get_local $2)
+       )
+      )
+     )
+     (return
+      (f32.const -9223372036854775808)
+     )
+    )
+   )
+  )
 )