From: Chandler Carruth <chandlerc@gmail.com>
Date: Mon, 4 Jan 2016 07:23:12 +0000 (+0000)
Subject: Fix a horrible infloop in value tracking in the face of dead code.
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=commitdiff_plain;h=ab99ec2ce71849d1976ac7497f671375a1900e97

Fix a horrible infloop in value tracking in the face of dead code.

Amazingly, we just never triggered this without:
1) Moving code around for MetadataTracking so that a certain *different*
   amount of inlining occurs in the per-TU compile step.
2) Then you LTO opt or clang with a bootstrap, and get inlining, loop
   opts, and GVN line up everything *just* right.

I don't really know how we didn't hit this before. We really need to be
fuzz testing stuff, it shouldn't be hard to trigger. I'm working on
crafting a reduced nice test case, and will submit that when I have it,
but I want to get LTO build bots going again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256735 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index d6a78411388..7e56f1ebe60 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -2830,7 +2830,12 @@ Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
                                               const DataLayout &DL) {
   unsigned BitWidth = DL.getPointerTypeSizeInBits(Ptr->getType());
   APInt ByteOffset(BitWidth, 0);
-  while (1) {
+
+  // We walk up the defs but use a visited set to handle unreachable code. In
+  // that case, we stop after accumulating the cycle once (not that it
+  // matters).
+  SmallPtrSet<Value *, 16> Visited;
+  while (Visited.insert(Ptr).second) {
     if (Ptr->getType()->isVectorTy())
       break;