diff --git a/llvm/lib/CodeGen/ValueTypes.cpp b/llvm/lib/CodeGen/ValueTypes.cpp
index e74068e22f4cd..6bb99f54fe9e0 100644
--- a/llvm/lib/CodeGen/ValueTypes.cpp
+++ b/llvm/lib/CodeGen/ValueTypes.cpp
@@ -252,6 +252,29 @@ MVT MVT::getVT(Type *Ty, bool HandleUnknown){
   default:
     if (HandleUnknown) return MVT(MVT::Other);
     llvm_unreachable("Unknown type!");
+  case Type::PointerTyID: {
+    if (HandleUnknown)
+      return MVT(MVT::Other);
+    // A pointer normally cannot be lowered to a value type without a
+    // DataLayout, so it is an "unknown" type here. The exception is the
+    // WebAssembly reference types: EVT::getTypeForEVT maps MVT::externref /
+    // MVT::funcref to opaque pointers in address spaces 10 and 20, and that
+    // mapping has to be invertible so that DataLayout-free EVT helpers can
+    // recover the element type of an <N x externref> / <N x funcref> vector
+    // during type legalization instead of crashing.
+    //
+    // Address spaces 10 and 20 are not reserved for WebAssembly, but a target
+    // only reaches this code with such a pointer if it first produced an
+    // externref/funcref MVT, which only WebAssembly does.
+    switch (cast<PointerType>(Ty)->getAddressSpace()) {
+    case 10:
+      return MVT(MVT::externref);
+    case 20:
+      return MVT(MVT::funcref);
+    default:
+      llvm_unreachable("Unknown type!");
+    }
+  }
   case Type::VoidTyID:
     return MVT::isVoid;
   case Type::ByteTyID:
diff --git a/llvm/test/Transforms/SLPVectorizer/WebAssembly/externref-no-vectorize.ll b/llvm/test/Transforms/SLPVectorizer/WebAssembly/externref-no-vectorize.ll
new file mode 100644
index 0000000000000..27298fb6ce4e9
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/WebAssembly/externref-no-vectorize.ll
@@ -0,0 +1,48 @@
+; RUN: opt < %s -passes=slp-vectorizer -mtriple=wasm32-unknown-unknown -S | FileCheck %s
+
+; A WebAssembly reference type cannot be vectorized.
+; This used to crash type legalization while the SLP vectorizer was computing
+; the cost for a <N x externref> value.
+
+target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-i128:128-n32:64-S128-ni:1:10:20"
+target triple = "wasm32-unknown-unknown"
+
+%externref = type ptr addrspace(10)
+
+declare %externref @foo()
+declare void @bar(%externref)
+
+; Two externref phis that feed two calls are candidates for being gathered into
+; a vector but they must be left scalar. Derived the following C code:
+;
+;   __externref_t foo(void);
+;   void bar(__externref_t);
+;   void test(int flag, __externref_t ref1, __externref_t ref2) {
+;     if (flag) {
+;       ref1 = foo();
+;       ref2 = foo();
+;     }
+;     bar(ref1); bar(ref2);
+;   }
+;
+; CHECK-LABEL: @test(
+; CHECK-NOT:   phi <{{.*}} x ptr addrspace(10)>
+; CHECK-NOT:   call void @bar(<{{.*}} x ptr addrspace(10)>
+; CHECK:       ret void
+define void @test(i32 %flag, %externref %ref1, %externref %ref2) {
+entry:
+  %c = icmp eq i32 %flag, 0
+  br i1 %c, label %join, label %then
+
+then:
+  %a = tail call %externref @foo()
+  %b = tail call %externref @foo()
+  br label %join
+
+join:
+  %p1 = phi %externref [ %a, %then ], [ %ref1, %entry ]
+  %p2 = phi %externref [ %b, %then ], [ %ref2, %entry ]
+  tail call void @bar(%externref %p1)
+  tail call void @bar(%externref %p2)
+  ret void
+}