3 files changed, 126 insertions, 1 deletions

diff --git a/src/passes/MergeBlocks.cpp b/src/passes/MergeBlocks.cpp
index ab368429f..1401cd2f4 100644
--- a/src/passes/MergeBlocks.cpp
+++ b/src/passes/MergeBlocks.cpp
@@ -129,6 +129,11 @@ struct ProblemFinder : public ControlFlowWalker<ProblemFinder> {
     }
   }
 
+  void visitBrOnExn(BrOnExn* curr) {
+    // We should not take exnref value out of br_on_exn
+    foundProblem = true;
+  }
+
   bool found() {
     assert(brIfs >= droppedBrIfs);
     return foundProblem || brIfs > droppedBrIfs;
@@ -526,6 +531,7 @@ struct MergeBlocks : public WalkerPass<PostWalker<MergeBlocks>> {
   void visitBreak(Break* curr) {
     optimize(curr, curr->condition, optimize(curr, curr->value), &curr->value);
   }
+
   void visitSwitch(Switch* curr) {
     optimize(curr, curr->condition, optimize(curr, curr->value), &curr->value);
   }
@@ -540,7 +546,6 @@ struct MergeBlocks : public WalkerPass<PostWalker<MergeBlocks>> {
       }
       outer = optimize(curr, curr->operands[i], outer);
     }
-    return;
   }
 
   void visitCall(Call* curr) { handleCall(curr); }
@@ -561,6 +566,22 @@ struct MergeBlocks : public WalkerPass<PostWalker<MergeBlocks>> {
     }
     optimize(curr, curr->target, outer);
   }
+
+  void visitThrow(Throw* curr) {
+    Block* outer = nullptr;
+    for (Index i = 0; i < curr->operands.size(); i++) {
+      if (EffectAnalyzer(
+            getPassOptions(), getModule()->features, curr->operands[i])
+            .hasSideEffects()) {
+        return;
+      }
+      outer = optimize(curr, curr->operands[i], outer);
+    }
+  }
+
+  void visitRethrow(Rethrow* curr) { optimize(curr, curr->exnref); }
+
+  void visitBrOnExn(BrOnExn* curr) { optimize(curr, curr->exnref); }
 };
 
 Pass* createMergeBlocksPass() { return new MergeBlocks(); }
diff --git a/test/passes/remove-unused-names_merge-blocks_enable-threads.txt b/test/passes/remove-unused-names_merge-blocks_all-features.txt
index cf37ebc9d..90a56d32d 100644
--- a/test/passes/remove-unused-names_merge-blocks_enable-threads.txt
+++ b/test/passes/remove-unused-names_merge-blocks_all-features.txt
@@ -1697,3 +1697,50 @@
   )
  )
 )
+(module
+ (type $none_=>_none (func))
+ (type $i32_=>_none (func (param i32)))
+ (type $none_=>_i32 (func (result i32)))
+ (event $e (attr 0) (param i32))
+ (func $foo
+  (nop)
+ )
+ (func $throw
+  (nop)
+  (throw $e
+   (i32.const 3)
+  )
+ )
+ (func $rethrow
+  (local $0 exnref)
+  (call $foo)
+  (rethrow
+   (local.get $0)
+  )
+ )
+ (func $br_on_exn (result i32)
+  (local $0 exnref)
+  (block $label$0 (result i32)
+   (call $foo)
+   (drop
+    (br_on_exn $label$0 $e
+     (local.get $0)
+    )
+   )
+   (i32.const 3)
+  )
+ )
+ (func $cannot_extract_br_on_exn_exnref
+  (local $0 exnref)
+  (drop
+   (block $label$0 (result i32)
+    (drop
+     (br_on_exn $label$0 $e
+      (local.get $0)
+     )
+    )
+    (i32.const 5)
+   )
+  )
+ )
+)
diff --git a/test/passes/remove-unused-names_merge-blocks_enable-threads.wast b/test/passes/remove-unused-names_merge-blocks_all-features.wast
index f9603a60d..9a6840650 100644
--- a/test/passes/remove-unused-names_merge-blocks_enable-threads.wast
+++ b/test/passes/remove-unused-names_merge-blocks_all-features.wast
@@ -1556,3 +1556,60 @@
   )
  )
 )
+
+(module
+  (event $e (attr 0) (param i32))
+  (func $foo)
+
+  ;; 'nop' within 'block' of `throw' can be hoisted
+  (func $throw
+    (throw $e
+      (block (result i32)
+        (nop)
+        (i32.const 3)
+      )
+    )
+  )
+
+  ;; 'call $foo' within 'block' of `rethrow' can be hoisted
+  (func $rethrow (local $0 exnref)
+    (rethrow
+      (block (result exnref)
+        (call $foo)
+        (local.get $0)
+      )
+    )
+  )
+
+  ;; 'call $foo' within 'block' of `br_on_exn' can be hoisted
+  (func $br_on_exn (result i32) (local $0 exnref)
+    (block $label$0 (result i32)
+      (drop
+        (br_on_exn $label$0 $e
+          (block (result exnref)
+            (call $foo)
+            (local.get $0)
+          )
+        )
+      )
+      (i32.const 3)
+    )
+  )
+
+  ;; Unlike br_if, br_on_exn's exnref argument itself cannot be extracted.
+  ;; Without proper handling for br_on_exn in ProblemFinder, this crashes.
+  (func $cannot_extract_br_on_exn_exnref (local $0 exnref)
+    (block
+      (drop
+        (block $label$0 (result i32)
+          (drop
+            (br_on_exn $label$0 $e
+              (local.get $0)
+            )
+          )
+          (i32.const 5)
+        )
+      )
+    )
+  )
+)