3 files changed, 14 insertions, 9 deletions
diff --git a/src/ir/properties.h b/src/ir/properties.h
index 63dd6c72c..8e5297092 100644
--- a/src/ir/properties.h
+++ b/src/ir/properties.h
@@ -328,6 +328,12 @@ inline bool isResultFallthrough(Expression* curr) {
          curr->is<Break>();
 }
 
+inline bool canEmitSelectWithArms(Expression* ifTrue, Expression* ifFalse) {
+  // A select only allows a single value in its arms in the spec:
+  // https://webassembly.github.io/spec/core/valid/instructions.html#xref-syntax-instructions-syntax-instr-parametric-mathsf-select-t-ast
+  return ifTrue->type.isSingle() && ifFalse->type.isSingle();
+}
+
 } // namespace Properties
 
 } // namespace wasm
diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 9f095b333..31ed9348a 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -3037,7 +3037,12 @@ private:
                                                        curr->ifTrue)
                                    .hasSideEffects();
 
-            if (validTypes && validEffects) {
+            // In addition, check for specific limitations of select.
+            bool validChildren =
+              !std::is_same<T, Select>::value ||
+              Properties::canEmitSelectWithArms(ifTrueChild, ifFalseChild);
+
+            if (validTypes && validEffects && validChildren) {
               // Replace ifTrue with its child.
               curr->ifTrue = ifTrueChild;
               // Relace ifFalse with its child, and reuse that node outside.
diff --git a/src/passes/RemoveUnusedBrs.cpp b/src/passes/RemoveUnusedBrs.cpp
index 157cfc1f3..d0950b485 100644
--- a/src/passes/RemoveUnusedBrs.cpp
+++ b/src/passes/RemoveUnusedBrs.cpp
@@ -97,12 +97,6 @@ static bool tooCostlyToRunUnconditionally(const PassOptions& passOptions,
   return total >= TOO_MUCH;
 }
 
-static bool canEmitSelectWithArms(Expression* ifTrue, Expression* ifFalse) {
-  // A select only allows a single value in its arms in the spec:
-  // https://webassembly.github.io/spec/core/valid/instructions.html#xref-syntax-instructions-syntax-instr-parametric-mathsf-select-t-ast
-  return ifTrue->type.isSingle() && ifFalse->type.isSingle();
-}
-
 struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
   bool isFunctionParallel() override { return true; }
 
@@ -1030,7 +1024,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
                       .hasSideEffects();
                   list[0] = old;
                   if (canReorder && !hasSideEffects &&
-                      canEmitSelectWithArms(br->value, curr)) {
+                      Properties::canEmitSelectWithArms(br->value, curr)) {
                     ExpressionManipulator::nop(list[0]);
                     replaceCurrent(
                       builder.makeSelect(br->condition, br->value, curr));
@@ -1055,7 +1049,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
         if (!iff->ifFalse) {
           return nullptr;
         }
-        if (!canEmitSelectWithArms(iff->ifTrue, iff->ifFalse)) {
+        if (!Properties::canEmitSelectWithArms(iff->ifTrue, iff->ifFalse)) {
           return nullptr;
         }
         if (iff->condition->type == Type::unreachable) {