Index: llvm/include/llvm/IR/IntrinsicsWebAssembly.td
===================================================================
--- llvm/include/llvm/IR/IntrinsicsWebAssembly.td
+++ llvm/include/llvm/IR/IntrinsicsWebAssembly.td
@@ -31,6 +31,8 @@
 //===----------------------------------------------------------------------===//
 def int_wasm_ref_null_extern : Intrinsic<[llvm_externref_ty], [], [IntrNoMem]>;
 def int_wasm_ref_null_func : Intrinsic<[llvm_funcref_ty], [], [IntrNoMem]>;
+def int_wasm_ref_is_null_extern : Intrinsic<[llvm_i32_ty], [llvm_externref_ty], [IntrNoMem]>;
+def int_wasm_ref_is_null_func : Intrinsic<[llvm_i32_ty], [llvm_funcref_ty], [IntrNoMem]>;
 
 //===----------------------------------------------------------------------===//
 // Table intrinsics
Index: llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmTypeCheck.cpp
===================================================================
--- llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmTypeCheck.cpp
+++ llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmTypeCheck.cpp
@@ -308,6 +308,11 @@
     Stack.insert(Stack.end(), Sig->Params.begin(), Sig->Params.end());
   } else if (Name == "unreachable") {
     Unreachable = true;
+  } else if (Name == "ref.is_null") {
+    // FIXME: overly permissive - accepts any value.
+    if (popType(ErrorLoc, {}))
+      return true;
+    Stack.push_back(wasm::ValType::I32);
   } else {
     // The current instruction is a stack instruction which doesn't have
     // explicit operands that indicate push/pop types, so we get those from
Index: llvm/lib/Target/WebAssembly/WebAssemblyInstrRef.td
===================================================================
--- llvm/lib/Target/WebAssembly/WebAssemblyInstrRef.td
+++ llvm/lib/Target/WebAssembly/WebAssemblyInstrRef.td
@@ -27,8 +27,18 @@
                      vt#".select\t$dst, $lhs, $rhs, $cond",
                      vt#".select", 0x1b>,
                    Requires<[HasReferenceTypes]>;
+  // Define register variants of ref.is_null for each reference type. A
+  // single stack variant of the instruction is defined later.
+  let isCodeGenOnly = 1 in
+  def REF_IS_NULL_#rc : NI<(outs I32:$dst), (ins rc:$ref),
+                           [(set I32:$dst, (!cast<Intrinsic>("int_wasm_ref_is_null_" # ht) rc:$ref))],
+                           "false",
+                           "">,
+                           Requires<[HasReferenceTypes]>;
 }
 
+def REF_IS_NULL_S : NI<(outs), (ins), [], "true", "ref.is_null", 0xd1>;
+
 defm "" : REF_I<FUNCREF, funcref, "func">;
 defm "" : REF_I<EXTERNREF, externref, "extern">;
 
Index: llvm/test/CodeGen/WebAssembly/ref-null.ll
===================================================================
--- llvm/test/CodeGen/WebAssembly/ref-null.ll
+++ llvm/test/CodeGen/WebAssembly/ref-null.ll
@@ -6,6 +6,8 @@
 
 declare %externref @llvm.wasm.ref.null.extern() nounwind
 declare %funcref @llvm.wasm.ref.null.func() nounwind
+declare i32 @llvm.wasm.ref.is_null.extern(%externref) nounwind
+declare i32 @llvm.wasm.ref.is_null.func(%funcref) nounwind
 
 define %externref @get_null_extern() {
 ; CHECK-LABEL: get_null_extern:
@@ -24,3 +26,23 @@
   %null = call %funcref @llvm.wasm.ref.null.func()
   ret %funcref %null
 }
+
+define i32 @ref_is_null_extern(%externref %eref) {
+  ; CHECK-LABEL: ref_is_null_extern:
+  ; CHECK-NEXT: .functype      ref_is_null_extern (externref) -> (i32)
+  %null = call %externref @llvm.wasm.ref.null.extern()
+  %is_null = call i32 @llvm.wasm.ref.is_null.extern(%externref %null)
+  %arg_is_null = call i32 @llvm.wasm.ref.is_null.extern(%externref %eref)
+  %res = add i32 %is_null, %arg_is_null
+  ret i32 %res
+}
+
+define i32 @ref_is_null_func(%funcref %fref) {
+  ; CHECK-LABEL: ref_is_null_func:
+  ; CHECK-NEXT: .functype      ref_is_null_func (funcref) -> (i32)
+  %null = call %funcref @llvm.wasm.ref.null.func()
+  %is_null = call i32 @llvm.wasm.ref.is_null.func(%funcref %null)
+  %arg_is_null = call i32 @llvm.wasm.ref.is_null.func(%funcref %fref)
+  %res = add i32 %is_null, %arg_is_null
+  ret i32 %res
+}
Index: llvm/test/MC/WebAssembly/reference-types.s
===================================================================
--- llvm/test/MC/WebAssembly/reference-types.s
+++ llvm/test/MC/WebAssembly/reference-types.s
@@ -1,6 +1,16 @@
 # RUN: llvm-mc -show-encoding -triple=wasm32-unknown-unknown -mattr=+reference-types < %s | FileCheck %s
 # RUN: llvm-mc -show-encoding -triple=wasm64-unknown-unknown -mattr=+reference-types < %s | FileCheck %s
 
+# CHECK-LABEL:ref_is_null:
+# CHECK: ref.is_null     # encoding: [0xd1]
+ref_is_null:
+  .functype ref_is_null () -> (i32, i32)
+  ref.null_extern
+  ref.is_null
+  ref.null_func
+  ref.is_null
+  end_function
+
 # CHECK-LABEL: ref_null_test:
 # CHECK: ref.null_func   # encoding: [0xd0,0x70]
 # CHECK: ref.null_extern # encoding: [0xd0,0x6f]
Index: llvm/test/MC/WebAssembly/type-checker-errors.s
===================================================================
--- llvm/test/MC/WebAssembly/type-checker-errors.s
+++ llvm/test/MC/WebAssembly/type-checker-errors.s
@@ -468,6 +468,19 @@
 # CHECK: :[[@LINE+1]]:3: error: 1 superfluous return values
   end_function
 
+ref_is_null_empty_stack_while_popping:
+  .functype ref_is_null_empty_stack_while_popping () -> ()
+# CHECK: [[@LINE+1]]:3: error: empty stack while popping value
+  ref.is_null
+  end_function
+
+ref_is_null_pushes_i32:
+  .functype ref_is_null_pushes_i32 () -> (i64)
+  ref.null_func
+  ref.is_null
+# CHECK: :[[@LINE+1]]:3: error: popped i32, expected i64
+  end_function
+
 # For the other instructions, the type checker checks vs the operands in the
 # instruction definition. Perform some simple checks for these rather than
 # exhaustively testing all instructions.