GUFA: Ignore unreachable packed reads (#8564)

Without this early return, we'd try to find the packed size in bits of
the unreachable type, which asserts.

Author: kripken

src/ir/possible-contents.cpp

@@ -3136,31 +3136,33 @@ void Flower::filterPackedDataReads(PossibleContents& contents,
   Expression* ref;
   Index index;
   unsigned bytes = 0;
-  Type resultType = Type::none;
   if (auto* get = expr->dynCast<StructGet>()) {
     signed_ = get->signed_;
     ref = get->ref;
     index = get->index;
-    resultType = get->type;
   } else if (auto* get = expr->dynCast<ArrayGet>()) {
     signed_ = get->signed_;
     ref = get->ref;
     // Arrays are treated as having a single field.
     index = 0;
-    resultType = get->type;
   } else if (auto* load = expr->dynCast<ArrayLoad>()) {
     signed_ = load->signed_;
     ref = load->ref;
     index = 0;
     bytes = load->bytes;
-    resultType = load->type;
   } else {
     WASM_UNREACHABLE("bad packed read");
   }
   if (!signed_) {
     return;
   }
 
+  Type resultType = expr->type;
+  if (resultType == Type::unreachable) {
+    // This read never executes.
+    return;
+  }
+
   // If there is no struct or array to read, no value will ever be returned.
   if (ref->type.isNull()) {
     contents = PossibleContents::none();

test/lit/passes/gufa-refs.wast

@@ -6141,6 +6141,25 @@
       )
     )
   )
+
+  ;; CHECK:      (func $unreachable (type $1)
+  ;; CHECK-NEXT:  (array.get_s $array
+  ;; CHECK-NEXT:   (array.new_default $array
+  ;; CHECK-NEXT:    (i32.const 0)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:   (unreachable)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $unreachable
+    ;; This array.get is unreachable, and when handling packing we should not
+    ;; error.
+    (array.get_s $array
+      (array.new_default $array
+        (i32.const 0)
+      )
+      (unreachable)
+    )
+  )
 )
 
 ;; Atomic accesses require special handling