[llvm-reduce] Add test for BB reduction with non-void ret type.

Precommit test for D86849.

llvm/test/Reduce/remove-bbs-ret-nonvoid.ll

@@ -0,0 +1,32 @@
+; Test that llvm-reduce inserts valid return instructions for functions with
+; on-void return types.
+;
+; RUN: llvm-reduce --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t
+; RUN: cat %t | FileCheck %s
+
+; CHECK-INTERESTINGNESS: interesting:
+; CHECK-INTERESTINGNESS: interesting2:
+
+define i32 @main(i1 %c) {
+; CHECK-LABEL: define i32 @main() {
+; CHECK-LABEL: interesting:
+; CHECK-NEXT:    br label %interesting2
+
+; CHECK-LABEL: interesting2:
+; CHECK-NEXT:    br label %uninteresting1
+
+; CHECK-LABEL: uninteresting1:
+; CHECK-NEXT:    ret i32 10
+
+interesting:
+  br label %interesting2
+
+interesting2:
+  br i1 true, label %uninteresting1, label %uninteresting
+
+uninteresting:
+  br label %uninteresting1
+
+uninteresting1:
+  ret i32 10
+}