[EH] Fix missing outer block for catchless try (#6519)

When translating a `try` expression, we may need an 'outer' block that
wraps the newly generated `try_table` so we can jump out of the
expression when an exception does not occur. (The condition we use is
when the `try` has any catches or if the `try` is a target of any
inner `try-delegate`s:
https://github.com/WebAssembly/binaryen/blob/219e668e87b012c0634043ed702534b8be31231f/src/passes/TranslateEH.cpp#L677)

In case the `try` has either of `catch` or `delegate`, when we have the
'outer' block, we add the newly created `try_table` in the 'outer' block
and replace the whole expression with the block:
https://github.com/WebAssembly/binaryen/blob/219e668e87b012c0634043ed702534b8be31231f/src/passes/TranslateEH.cpp#L670
https://github.com/WebAssembly/binaryen/blob/219e668e87b012c0634043ed702534b8be31231f/src/passes/TranslateEH.cpp#L332-L340

But in case of a catchless `try`, we forgot to do that:
https://github.com/WebAssembly/binaryen/blob/219e668e87b012c0634043ed702534b8be31231f/src/passes/TranslateEH.cpp#L388

So this PR fixes it.

2 files changed, 62 insertions, 8 deletions

diff --git a/src/passes/TranslateEH.cpp b/src/passes/TranslateEH.cpp
index 33fa4689d..f8e059624 100644
--- a/src/passes/TranslateEH.cpp
+++ b/src/passes/TranslateEH.cpp
@@ -215,7 +215,9 @@ struct TranslateToNewEH : public WalkerPass<PostWalker<TranslateToNewEH>> {
   // current 'try' into 'try_table' yet; it only adds block, br, and throw_ref
   // instructions to complete the conversions of inner try~delegates that target
   // the current try.
-  void processDelegateTarget(Try* curr, Block* outerBlock) {
+  void processDelegateTarget(Try* curr,
+                             Block* outerBlock,
+                             bool& outerBlockUsedSoFar) {
     Builder builder(*getModule());
 
     // Convert
@@ -291,10 +293,12 @@ struct TranslateToNewEH : public WalkerPass<PostWalker<TranslateToNewEH>> {
     Name delegateBrTarget = delegateTargetToBrTarget[curr->name];
     Expression* innerBody = nullptr;
     if (curr->type.isConcrete()) {
+      outerBlockUsedSoFar = true;
       auto* brToOuter = builder.makeBreak(outerBlock->name, curr->body);
       innerBody = builder.blockifyWithName(
         brToOuter, delegateBrTarget, nullptr, Type(HeapType::exn, Nullable));
     } else {
+      outerBlockUsedSoFar = curr->body->type != Type::unreachable;
       auto* brToOuter = curr->body->type == Type::unreachable
                           ? nullptr
                           : builder.makeBreak(outerBlock->name);
@@ -304,7 +308,7 @@ struct TranslateToNewEH : public WalkerPass<PostWalker<TranslateToNewEH>> {
     curr->body = builder.makeThrowRef(innerBody);
   }
 
-  void processDelegate(Try* curr, Block* outerBlock) {
+  void processDelegate(Try* curr, Block* outerBlock, bool outerBlockUsedSoFar) {
     Builder builder(*getModule());
     // Convert
     // (try
@@ -332,7 +336,7 @@ struct TranslateToNewEH : public WalkerPass<PostWalker<TranslateToNewEH>> {
     // If we need an outer block for other reasons (if this is a target of a
     // delegate), we insert the new try_table into it. If not we just replace
     // the current try with the new try_table.
-    if (outerBlock) {
+    if (outerBlock && outerBlockUsedSoFar) {
       outerBlock->list.push_back(tryTable);
       replaceCurrent(outerBlock);
     } else {
@@ -340,7 +344,7 @@ struct TranslateToNewEH : public WalkerPass<PostWalker<TranslateToNewEH>> {
     }
   }
 
-  void processCatches(Try* curr, Block* outerBlock) {
+  void processCatches(Try* curr, Block* outerBlock, bool outerBlockUsedSoFar) {
     Module* wasm = getModule();
     Builder builder(*wasm);
 
@@ -385,7 +389,15 @@ struct TranslateToNewEH : public WalkerPass<PostWalker<TranslateToNewEH>> {
 
     // If we don't have any catches, we don't need to do more.
     if (curr->catchBodies.empty()) { // catch-less try
-      replaceCurrent(tryTable);
+      // If we need an outer block for other reasons (if this is a target of a
+      // delegate), we insert the new try_table into it. If not we just replace
+      // the current try with the new try_table.
+      if (outerBlock && outerBlockUsedSoFar) {
+        outerBlock->list.push_back(tryTable);
+        replaceCurrent(outerBlock);
+      } else {
+        replaceCurrent(tryTable);
+      }
       return;
     }
 
@@ -679,13 +691,14 @@ struct TranslateToNewEH : public WalkerPass<PostWalker<TranslateToNewEH>> {
         builder.makeBlock(labels->getUnique("outer"), {}, curr->type);
     }
 
+    bool outerBlockUsedSoFar = false;
     if (it != delegateTargetToBrTarget.end()) {
-      processDelegateTarget(curr, outerBlock);
+      processDelegateTarget(curr, outerBlock, outerBlockUsedSoFar);
     }
     if (curr->isDelegate()) {
-      processDelegate(curr, outerBlock);
+      processDelegate(curr, outerBlock, outerBlockUsedSoFar);
     } else { // try-catch or catch-less try
-      processCatches(curr, outerBlock);
+      processCatches(curr, outerBlock, outerBlockUsedSoFar);
     }
   }
 
diff --git a/test/lit/passes/translate-to-new-eh.wast b/test/lit/passes/translate-to-new-eh.wast
index b1bbb4b98..ba3997951 100644
--- a/test/lit/passes/translate-to-new-eh.wast
+++ b/test/lit/passes/translate-to-new-eh.wast
@@ -2170,4 +2170,45 @@
       (unreachable)
     )
   )
+
+  ;; CHECK:      (func $try-delegate-within-catchless-try (type $1)
+  ;; CHECK-NEXT:  (block $outer1
+  ;; CHECK-NEXT:   (try_table
+  ;; CHECK-NEXT:    (throw_ref
+  ;; CHECK-NEXT:     (block $l00 (result exnref)
+  ;; CHECK-NEXT:      (try_table (catch_all_ref $l00)
+  ;; CHECK-NEXT:       (call $foo)
+  ;; CHECK-NEXT:      )
+  ;; CHECK-NEXT:      (br $outer1)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  ;; STACKIR-OPT:      (func $try-delegate-within-catchless-try (type $1)
+  ;; STACKIR-OPT-NEXT:  block $outer1
+  ;; STACKIR-OPT-NEXT:   try_table
+  ;; STACKIR-OPT-NEXT:    block $l00 (result exnref)
+  ;; STACKIR-OPT-NEXT:     try_table (catch_all_ref $l00)
+  ;; STACKIR-OPT-NEXT:      call $foo
+  ;; STACKIR-OPT-NEXT:     end
+  ;; STACKIR-OPT-NEXT:     br $outer1
+  ;; STACKIR-OPT-NEXT:    end
+  ;; STACKIR-OPT-NEXT:    throw_ref
+  ;; STACKIR-OPT-NEXT:   end
+  ;; STACKIR-OPT-NEXT:   unreachable
+  ;; STACKIR-OPT-NEXT:  end
+  ;; STACKIR-OPT-NEXT: )
+  (func $try-delegate-within-catchless-try
+    (try $l0
+      (do
+        (try
+          (do
+            (call $foo)
+          )
+          (delegate $l0)
+        )
+      )
+    )
+  )
 )