From e5dc57d4fb356db31476da8717f20e9f5dc58ac6 Mon Sep 17 00:00:00 2001
From: Nadav Rotem <nrotem@apple.com>
Date: Sat, 20 Oct 2012 20:45:01 +0000
Subject: [PATCH] Fix an infinite loop in the loop-vectorizer.

PR14134.

llvm-svn: 166379
---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp      |  6 ++++++
 .../Transforms/LoopVectorize/2012-10-20-infloop.ll   | 12 ++++++++++++
 2 files changed, 18 insertions(+)
 create mode 100644 llvm/test/Transforms/LoopVectorize/2012-10-20-infloop.ll

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index c11c66f1aeb5..027fe0656be5 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -1175,6 +1175,12 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
     bool FoundInBlockUser = false;
     // Did we reach the initial PHI node ?
     bool FoundStartPHI = false;
+
+    // If the instruction has no users then this is a broken
+    // chain and can't be a reduction variable.
+    if (Iter->use_begin() == Iter->use_end())
+      return false;
+
     // For each of the *users* of iter.
     for (Value::use_iterator it = Iter->use_begin(), e = Iter->use_end();
          it != e; ++it) {
diff --git a/llvm/test/Transforms/LoopVectorize/2012-10-20-infloop.ll b/llvm/test/Transforms/LoopVectorize/2012-10-20-infloop.ll
new file mode 100644
index 000000000000..16a77291995d
--- /dev/null
+++ b/llvm/test/Transforms/LoopVectorize/2012-10-20-infloop.ll
@@ -0,0 +1,12 @@
+; RUN: opt < %s  -loop-vectorize -dce
+
+; Check that we don't fall into an infinite loop.
+define void @test() nounwind {
+entry:
+ br label %for.body
+
+for.body:
+ %0 = phi i32 [ 1, %entry ], [ 0, %for.body ]
+ br label %for.body
+}
+