[AVR] Add a regression test for struct return lowering

The test is taken from
avr-rust/rust-legacy-fork#57

The originally implementation of struct return lowering was made in
r325474.

Patch by Peter Nimmervoll

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327967 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/AVR/lower-formal-args-struct-return.ll

@@ -0,0 +1,21 @@
+; RUN: llc < %s -march=avr | FileCheck %s
+
+; This test ensures that the backend can lower returns of struct values.
+; It does not check how these are lowered.
+;
+; In the past, this code used to return an error
+;
+; Assertion `InVals.size() == Ins.size() && "LowerFormalArguments didn't emit the correct number of values!"' failed.
+;
+; This feature was first implemented in r325474.
+
+declare i8 @do_something(i8 %val)
+
+; CHECK-LABEL: main
+define { i1, i8 } @main(i8) #2 {
+entry:
+  %1 = call zeroext i8 @do_something(i8 zeroext %0)
+  %2 = insertvalue { i1, i8 } { i1 true, i8 undef }, i8 %1, 1
+  ret { i1, i8 } %2
+}
+