From 692ad8dd0630f80babeb631ec8ae5bf6b54456cd Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Thu, 5 Nov 2009 19:44:06 +0000
Subject: [PATCH] Teach LoopUnroll how to bail if LoopSimplify can't give it
 what it needs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86164 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/LoopUnroll.cpp | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index d68427afce7..3c58abe37e0 100644
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -108,8 +108,19 @@ static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI) {
 bool llvm::UnrollLoop(Loop *L, unsigned Count, LoopInfo* LI, LPPassManager* LPM) {
   assert(L->isLCSSAForm());
 
-  BasicBlock *Header = L->getHeader();
+  BasicBlock *Preheader = L->getLoopPreheader();
+  if (!Preheader) {
+    DEBUG(errs() << "  Can't unroll; loop preheader-insertion failed.\n");
+    return false;
+  }
+
   BasicBlock *LatchBlock = L->getLoopLatch();
+  if (!LatchBlock) {
+    DEBUG(errs() << "  Can't unroll; loop exit-block-insertion failed.\n");
+    return false;
+  }
+
+  BasicBlock *Header = L->getHeader();
   BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
   
   if (!BI || BI->isUnconditional()) {