[LoopReroll] Don't crash on dead code

If a PHI has no users, don't crash; bail gracefully. This shouldn't
happen often, but we can make no guarantees that previous passes didn't leave
dead code around.

llvm-svn: 229405

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp b/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
index 852f3ed9d51..704299f3041 100644
--- a/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
@@ -511,6 +511,8 @@ void LoopReroll::SimpleLoopReduction::add(Loop *L) {
   // (including the PHI), except for the last value (which is used by the PHI
   // and also outside the loop).
   Instruction *C = Instructions.front();
+  if (C->user_empty())
+    return;
 
   do {
     C = cast<Instruction>(*C->user_begin());