2 files changed, 50 insertions, 1 deletions
diff --git a/test/CodeGen/MIR/ARM/ifcvt_canFallThroughTo.mir b/test/CodeGen/MIR/ARM/ifcvt_canFallThroughTo.mir
index 5a1583f7a9b..90d606a162d 100644
--- a/test/CodeGen/MIR/ARM/ifcvt_canFallThroughTo.mir
+++ b/test/CodeGen/MIR/ARM/ifcvt_canFallThroughTo.mir
@@ -52,8 +52,9 @@ body:             |
 #CHECK:     B %bb.3
 
 # Empty bb.2, originally containing "unreachable" and thus has no successors
+# and we cannot guess them: we should print an empty list of successors.
 #CHECK:   bb.2:
-#CHECK-NOT: successors
+#CHECK: successors:{{ *$}}
 
 #CHECK:   bb.3:
 #CHECK:     successors: %bb.1
diff --git a/test/CodeGen/MIR/X86/unreachable_block.ll b/test/CodeGen/MIR/X86/unreachable_block.ll
new file mode 100644
index 00000000000..4cea0392255
--- /dev/null
+++ b/test/CodeGen/MIR/X86/unreachable_block.ll
@@ -0,0 +1,48 @@
+; RUN: llc -mtriple x86_64-- -stop-before peephole-opt -o %t.mir %s
+; RUN: llc -mtriple x86_64-- -run-pass none %t.mir -verify-machineinstrs -o - | FileCheck %s
+
+; Unreachable blocks in the machine instr representation are these
+; weird empty blocks with no successors.
+; The MIR printer used to not print empty lists of successors. However,
+; the MIR parser now treats non-printed list of successors as "please
+; guess it for me". As a result, the parser tries to guess the list of
+; successors and given the block is empty, just assumes it falls through
+; the next block.
+;
+; The following test case used to fail the verifier because the false
+; path ended up falling through split.true and now, the definition of
+; %v does not dominate all its uses.
+; Indeed, we go from the following CFG:
+;          entry
+;         /      \
+;    true (def)   false
+;        |
+;  split.true (use)
+;
+; To this one:
+;          entry
+;         /      \
+;    true (def)   false
+;        |        /  <-- invalid edge
+;  split.true (use)
+;
+; Because of the invalid edge, we get the "def does not
+; dominate all uses" error.
+;
+; CHECK-LABEL: name: foo
+; CHECK-LABEL: bb.{{[0-9]+}}.false:
+; CHECK-NEXT: successors:
+; CHECK-NOT: %bb.{{[0-9]+}}.split.true
+; CHECK-LABEL: bb.{{[0-9]+}}.split.true:
+define void @foo(i32* %bar) {
+  br i1 undef, label %true, label %false
+true:
+  %v = load i32, i32* %bar
+  br label %split.true
+false:
+  unreachable
+split.true:
+  %vInc = add i32 %v, 1
+  store i32 %vInc, i32* %bar
+  ret void
+}