2 files changed, 21 insertions, 32 deletions

diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index 64c7fda02..e295d3931 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -865,7 +865,16 @@ void FunctionValidator::visitIf(If* curr) {
                       curr,
                       "returning if-else's false must have right type");
     } else {
-      if (curr->condition->type != Type::unreachable) {
+      if (curr->condition->type == Type::unreachable) {
+        shouldBeTrue(
+          curr->ifTrue->type == Type::unreachable ||
+            curr->ifFalse->type == Type::unreachable ||
+            (curr->ifTrue->type == Type::none &&
+             curr->ifFalse->type == Type::none) ||
+            Type::hasLeastUpperBound(curr->ifTrue->type, curr->ifFalse->type),
+          curr,
+          "arms of unreachable if-else must have compatible types");
+      } else {
         shouldBeEqual(curr->ifTrue->type,
                       Type(Type::unreachable),
                       curr,
@@ -876,18 +885,6 @@ void FunctionValidator::visitIf(If* curr) {
                       "unreachable if-else must have unreachable false");
       }
     }
-    if (curr->ifTrue->type.isConcrete()) {
-      shouldBeSubType(curr->ifTrue->type,
-                      curr->type,
-                      curr,
-                      "if type must match concrete ifTrue");
-    }
-    if (curr->ifFalse->type.isConcrete()) {
-      shouldBeSubType(curr->ifFalse->type,
-                      curr->type,
-                      curr,
-                      "if type must match concrete ifFalse");
-    }
   }
 }
 
diff --git a/src/wasm/wasm.cpp b/src/wasm/wasm.cpp
index f89ef80c2..38f35411f 100644
--- a/src/wasm/wasm.cpp
+++ b/src/wasm/wasm.cpp
@@ -215,28 +215,20 @@ void Block::finalize(std::optional<Type> type_, Breakability breakability) {
 }
 
 void If::finalize(std::optional<Type> type_) {
-  if (type_) {
-    type = *type_;
-    if (type == Type::none && (condition->type == Type::unreachable ||
-                               (ifFalse && ifTrue->type == Type::unreachable &&
-                                ifFalse->type == Type::unreachable))) {
-      type = Type::unreachable;
-    }
+  // The If is unreachable if the condition is unreachable or both arms are
+  // unreachable.
+  if (condition->type == Type::unreachable ||
+      (ifFalse && ifTrue->type == Type::unreachable &&
+       ifFalse->type == Type::unreachable)) {
+    type = Type::unreachable;
     return;
   }
 
-  type = ifFalse ? Type::getLeastUpperBound(ifTrue->type, ifFalse->type)
-                 : Type::none;
-  // if the arms return a value, leave it even if the condition
-  // is unreachable, we still mark ourselves as having that type, e.g.
-  // (if (result i32)
-  //  (unreachable)
-  //  (i32.const 10)
-  //  (i32.const 20)
-  // )
-  // otherwise, if the condition is unreachable, so is the if
-  if (type == Type::none && condition->type == Type::unreachable) {
-    type = Type::unreachable;
+  if (type_) {
+    type = *type_;
+  } else {
+    type = ifFalse ? Type::getLeastUpperBound(ifTrue->type, ifFalse->type)
+                   : Type::none;
   }
 }