fix break value removal in merge-blocks: a br_if's type changes without a value, so finalize the node, and remove the drop

2 files changed, 16 insertions, 9 deletions

diff --git a/src/passes/MergeBlocks.cpp b/src/passes/MergeBlocks.cpp
index f7fac9594..edfa1336b 100644
--- a/src/passes/MergeBlocks.cpp
+++ b/src/passes/MergeBlocks.cpp
@@ -116,8 +116,17 @@ struct BreakValueDropper : public ControlFlowWalker<BreakValueDropper, Visitor<B
   void visitBreak(Break* curr) {
     if (curr->value && curr->name == origin) {
       Builder builder(*getModule());
-      replaceCurrent(builder.makeSequence(builder.makeDrop(curr->value), curr));
+      auto* value = curr->value;
       curr->value = nullptr;
+      curr->finalize();
+      replaceCurrent(builder.makeSequence(builder.makeDrop(value), curr));
+    }
+  }
+
+  void visitDrop(Drop* curr) {
+    // if we dropped a br_if whose value we removed, then we are now dropping a (block (drop value) (br_if)) with type none, which does not need a drop
+    if (curr->value->type == none) {
+      replaceCurrent(curr->value);
     }
   }
 };
diff --git a/test/passes/merge-blocks.txt b/test/passes/merge-blocks.txt
index 152e6fbae..1116e0d28 100644
--- a/test/passes/merge-blocks.txt
+++ b/test/passes/merge-blocks.txt
@@ -29,14 +29,12 @@
   (func $drop-block-br-if (type $0)
     (block $block
       (block $x
-        (drop
-          (block i32
-            (drop
-              (i32.const 1)
-            )
-            (br_if $x
-              (i32.const 2)
-            )
+        (block
+          (drop
+            (i32.const 1)
+          )
+          (br_if $x
+            (i32.const 2)
           )
         )
         (drop