1 files changed, 58 insertions, 0 deletions
diff --git a/llvm/test/CodeGen/AVR/select-must-add-unconditional-jump.ll b/llvm/test/CodeGen/AVR/select-must-add-unconditional-jump.ll
new file mode 100644
index 00000000000..5c675b26614
--- /dev/null
+++ b/llvm/test/CodeGen/AVR/select-must-add-unconditional-jump.ll
@@ -0,0 +1,58 @@
+; RUN: llc -march=avr -print-after=expand-isel-pseudos < %s 2>&1 | FileCheck %s
+
+; Because `switch` seems to trigger Machine Basic Blocks to be ordered
+; in a different order than they were constructed, this exposes an
+; error in the `expand-isel-pseudos` pass. Specifically, it thought we
+; could always fallthrough to a newly-constructed MBB. However,
+; there's no guarantee that either of the constructed MBBs need to
+; occur immediately after the currently-focused one!
+;
+; This issue manifests in a CFG that looks something like this:
+;
+; BB#2: derived from LLVM BB %finish
+;     Predecessors according to CFG: BB#0 BB#1
+;         %vreg0<def> = PHI %vreg3, <BB#0>, %vreg5, <BB#1>
+;         %vreg7<def> = LDIRdK 2
+;         %vreg8<def> = LDIRdK 1
+;         CPRdRr %vreg2, %vreg0, %SREG<imp-def>
+;         BREQk <BB#6>, %SREG<imp-use>
+;     Successors according to CFG: BB#5(?%) BB#6(?%)
+;
+; The code assumes it the fallthrough block after this is BB#5, but
+; it's actually BB#3! To be proper, there should be an unconditional
+; jump tying this block to BB#5.
+
+define i8 @select_must_add_unconditional_jump(i8 %arg0, i8 %arg1) unnamed_addr {
+entry-block:
+  switch i8 %arg0, label %dead [
+    i8 0, label %zero
+    i8 1, label %one
+  ]
+
+zero:
+  br label %finish
+
+one:
+  br label %finish
+
+finish:
+  %predicate = phi i8 [ 50, %zero ], [ 100, %one ]
+  %is_eq = icmp eq i8 %arg1, %predicate
+  %result = select i1 %is_eq, i8 1, i8 2
+  ret i8 %result
+
+dead:
+  ret i8 0
+}
+
+; This check may be a bit brittle, but the important thing is that the
+; basic block containing `select` needs to contain explicit jumps to
+; both successors.
+
+; CHECK: BB#2: derived from LLVM BB %finish
+; CHECK: BREQk <[[BRANCHED:BB#[0-9]+]]>
+; CHECK: RJMPk <[[DIRECT:BB#[0-9]+]]>
+; CHECK: Successors according to CFG
+; CHECK-SAME-DAG: {{.*}}[[BRANCHED]]
+; CHECK-SAME-DAG: {{.*}}[[DIRECT]]
+; CHECK: BB#3: derived from LLVM BB