[AutoUpgrade] Don't try to upgrade struct return of non-intrinsic

This code should only be run for intrinsics known to LLVM (otherwise
it will crash), not for everything that starts with "llvm.".

Author: nikic

llvm/lib/IR/AutoUpgrade.cpp

@@ -1293,7 +1293,8 @@ static bool UpgradeIntrinsicFunction1(Function *F, Function *&NewFn) {
   }
 
   auto *ST = dyn_cast<StructType>(F->getReturnType());
-  if (ST && (!ST->isLiteral() || ST->isPacked())) {
+  if (ST && (!ST->isLiteral() || ST->isPacked()) &&
+      F->getIntrinsicID() != Intrinsic::not_intrinsic) {
     // Replace return type with literal non-packed struct. Only do this for
     // intrinsics declared to return a struct, not for intrinsics with
     // overloaded return type, in which case the exact struct type will be

llvm/test/Assembler/struct-ret-without-upgrade.ll

@@ -15,4 +15,15 @@ define %ty @test(%ty %arg) {
   ret %ty %copy
 }
 
+define %ty @test_not_real_intrinsic() {
+; CHECK-LABEL: @test_not_real_intrinsic(
+; CHECK-NEXT:    [[RET:%.*]] = call [[TY:%.*]] @llvm.dummy()
+; CHECK-NEXT:    ret [[TY]] [[RET]]
+;
+  %ret = call %ty @llvm.dummy()
+  ret %ty %ret
+}
+
+declare %ty @llvm.dummy()
+
 declare %ty @llvm.ssa.copy.s_tys(%ty)