3 files changed, 18 insertions, 8 deletions
diff --git a/src/literal.h b/src/literal.h
index c37f74499..1151abd2c 100644
--- a/src/literal.h
+++ b/src/literal.h
@@ -38,6 +38,9 @@ class Literal {
   // store only integers, whose bits are deterministic. floats
   // can have their signalling bit set, for example.
   union {
+    // Note: i31 is stored in the |i32| field, with the lower 31 bits containing
+    // the value if there is one, and the highest bit containing whether there
+    // is a value. Thus, a null is |i32 === 0|.
     int32_t i32;
     int64_t i64;
     uint8_t v128[16];
@@ -111,6 +114,9 @@ public:
       if (isData()) {
         return !gcData;
       }
+      if (type.getHeapType() == HeapType::i31) {
+        return i32 == 0;
+      }
       return true;
     }
     return false;
@@ -257,7 +263,7 @@ public:
   }
   static Literal makeI31(int32_t value) {
     auto lit = Literal(Type(HeapType::i31, NonNullable));
-    lit.i32 = value & 0x7fffffff;
+    lit.i32 = value | 0x80000000;
     return lit;
   }
 
@@ -276,7 +282,8 @@ public:
   }
   int32_t geti31(bool signed_ = true) const {
     assert(type.getHeapType() == HeapType::i31);
-    return signed_ ? (i32 << 1) >> 1 : i32;
+    // Cast to unsigned for the left shift to avoid undefined behavior.
+    return signed_ ? int32_t((uint32_t(i32) << 1)) >> 1 : (i32 & 0x7fffffff);
   }
   int64_t geti64() const {
     assert(type == Type::i64);
diff --git a/src/wasm-interpreter.h b/src/wasm-interpreter.h
index eb5dcd5a7..399910e7a 100644
--- a/src/wasm-interpreter.h
+++ b/src/wasm-interpreter.h
@@ -1419,6 +1419,9 @@ public:
     }
     const auto& value = flow.getSingleValue();
     NOTE_EVAL1(value);
+    if (value.isNull()) {
+      trap("null ref");
+    }
     return Literal(value.geti31(curr->signed_));
   }
 
diff --git a/src/wasm/literal.cpp b/src/wasm/literal.cpp
index 85e93f912..608018d8b 100644
--- a/src/wasm/literal.cpp
+++ b/src/wasm/literal.cpp
@@ -229,11 +229,7 @@ Literals Literal::makeNegOnes(Type type) {
 Literal Literal::makeZero(Type type) {
   assert(type.isSingle());
   if (type.isRef()) {
-    if (type.getHeapType() == HeapType::i31) {
-      return makeI31(0);
-    } else {
-      return makeNull(type.getHeapType());
-    }
+    return makeNull(type.getHeapType());
   } else if (type.isRtt()) {
     return Literal(type);
   } else {
@@ -515,7 +511,11 @@ std::ostream& operator<<(std::ostream& o, Literal literal) {
           o << "eqref(null)";
           break;
         case HeapType::i31:
-          o << "i31ref(" << literal.geti31() << ")";
+          if (literal.isNull()) {
+            o << "i31ref(null)";
+          } else {
+            o << "i31ref(" << literal.geti31() << ")";
+          }
           break;
         case HeapType::func:
         case HeapType::data: