Index: llvm/lib/IR/AutoUpgrade.cpp
===================================================================
--- llvm/lib/IR/AutoUpgrade.cpp
+++ llvm/lib/IR/AutoUpgrade.cpp
@@ -2042,13 +2042,17 @@
 /// Upgrade a call to an old intrinsic. All argument and return casting must be
 /// provided to seamlessly integrate with existing context.
 void llvm::UpgradeIntrinsicCall(CallBase *CI, Function *NewFn) {
-  Function *F = CI->getCalledFunction();
+  // Note dyn_cast to Function is not quite the same as getCalledFunction, which
+  // checks the callee's function type matches. It's likely we need to handle
+  // type changes here.
+  Function *F = dyn_cast<Function>(CI->getCalledOperand());
+  if (!F)
+    return;
+
   LLVMContext &C = CI->getContext();
   IRBuilder<> Builder(C);
   Builder.SetInsertPoint(CI->getParent(), CI->getIterator());
 
-  assert(F && "Intrinsic call is not direct?");
-
   if (!NewFn) {
     // Get the Function's name.
     StringRef Name = F->getName();
@@ -3909,21 +3913,29 @@
     }
 
     // This must be an upgrade from a named to a literal struct.
-    auto *OldST = cast<StructType>(CI->getType());
-    assert(OldST != NewFn->getReturnType() && "Return type must have changed");
-    assert(OldST->getNumElements() ==
-               cast<StructType>(NewFn->getReturnType())->getNumElements() &&
-           "Must have same number of elements");
-
-    SmallVector<Value *> Args(CI->args());
-    Value *NewCI = Builder.CreateCall(NewFn, Args);
-    Value *Res = PoisonValue::get(OldST);
-    for (unsigned Idx = 0; Idx < OldST->getNumElements(); ++Idx) {
-      Value *Elem = Builder.CreateExtractValue(NewCI, Idx);
-      Res = Builder.CreateInsertValue(Res, Elem, Idx);
+    if (auto *OldST = dyn_cast<StructType>(CI->getType())) {
+      assert(OldST != NewFn->getReturnType() &&
+             "Return type must have changed");
+      assert(OldST->getNumElements() ==
+                 cast<StructType>(NewFn->getReturnType())->getNumElements() &&
+             "Must have same number of elements");
+
+      SmallVector<Value *> Args(CI->args());
+      Value *NewCI = Builder.CreateCall(NewFn, Args);
+      Value *Res = PoisonValue::get(OldST);
+      for (unsigned Idx = 0; Idx < OldST->getNumElements(); ++Idx) {
+        Value *Elem = Builder.CreateExtractValue(NewCI, Idx);
+        Res = Builder.CreateInsertValue(Res, Elem, Idx);
+      }
+      CI->replaceAllUsesWith(Res);
+      CI->eraseFromParent();
+      return;
     }
-    CI->replaceAllUsesWith(Res);
-    CI->eraseFromParent();
+
+    // We're probably about to produce something invalid. Let the verifier catch
+    // it instead of dying here.
+    CI->setCalledOperand(
+        ConstantExpr::getPointerCast(NewFn, CI->getCalledOperand()->getType()));
     return;
   };
   CallInst *NewCall = nullptr;
Index: llvm/test/Assembler/autoupgrade-invalid-name-mangling.ll
===================================================================
--- /dev/null
+++ llvm/test/Assembler/autoupgrade-invalid-name-mangling.ll
@@ -0,0 +1,14 @@
+; RUN: not llvm-as < %s 2>&1 | FileCheck %s
+
+; CHECK: Intrinsic called with incompatible signature
+; CHECK-NEXT: %reg = call i32 @llvm.read_register.i64(
+; CHECK: Invalid user of intrinsic instruction!
+; CHECK-NEXT: %reg = call i32 @llvm.read_register.i64(
+define i32 @read_register_missing_mangling() {
+  %reg = call i32 @llvm.read_register(metadata !0)
+  ret i32 %reg
+}
+
+declare i64 @llvm.read_register(metadata)
+
+!0 = !{!"foo"}