[Test] Add failing test that demonstrates buggy behavior of ADCE

ADCE messes up with loop info (proved for new pass manager only) by
making some loop blocks unreachable, without making proper updates
to the loop.

Author: xortator

llvm/test/Transforms/ADCE/broken-loop-info.ll

@@ -0,0 +1,30 @@
+; RUN: opt -passes='loop(licm),adce,loop(licm)' -S < %s | FileCheck %s
+;
+; XFAIL: *
+; REQUIRES: asserts
+;
+; This test demonstrates a bug in ADCE's work with loop info. It does some
+; changes that make loop's block unreachable, but never bothers to update
+; loop info accordingly.
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128-ni:1-p2:32:8:8:32-ni:2"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @test() {
+; CHECK-LABEL: test
+
+bb:
+  br label %bb2
+
+bb1:                                              ; preds = %bb4
+  ret void
+
+bb2:                                              ; preds = %bb4, %bb
+  br i1 undef, label %bb4, label %bb3
+
+bb3:                                              ; preds = %bb2
+  br label %bb4
+
+bb4:                                              ; preds = %bb3, %bb2
+  br i1 undef, label %bb1, label %bb2
+}