From 9853db7072b26c57ab20bc17bbc00e7384abbf06 Mon Sep 17 00:00:00 2001
From: Zhou Sheng <zhousheng00@gmail.com>
Date: Mon, 26 Nov 2012 05:45:53 +0000
Subject: [PATCH] Fix a PassManager pointer use-after-free bug. The bug can be
 triggered when we require LoopInfo analysis ahead of DominatorTree
 construction in a Module Pass. The cause is that the LoopInfo analysis itself
 also invokes DominatorTree construction, therefore, when PassManager
 schedules LoopInfo, it will add DominatorTree first. Then after that, when
 the PassManger turns to schedule DominatorTree invoked by the above
 ModulePass, it finds there is already a DominatorTree, so it delete the
 redundant one. However, somehow it still try to access that pass pointer
 after free as code pasted below, which results in segment fault.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168581 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/VMCore/PassManager.cpp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/lib/VMCore/PassManager.cpp b/lib/VMCore/PassManager.cpp
index 8362034fcf2..3a8a9e25e3c 100644
--- a/lib/VMCore/PassManager.cpp
+++ b/lib/VMCore/PassManager.cpp
@@ -1654,6 +1654,18 @@ void MPPassManager::addLowerLevelRequiredPass(Pass *P, Pass *RequiredPass) {
 
     OnTheFlyManagers[P] = FPP;
   }
+
+  // If RequiredPass is an analysis pass and it is available then do not
+  // generate the analysis again. Stale analysis info should not be
+  // available at this point.
+  const PassInfo *PI =
+    PassRegistry::getPassRegistry()->getPassInfo(RequiredPass->getPassID());
+  if (PI && PI->isAnalysis() && 
+      FPP->getTopLevelManager()->findAnalysisPass(RequiredPass->getPassID())) {
+    delete RequiredPass;
+    return;
+  }
+
   FPP->add(RequiredPass);
 
   // Register P as the last user of RequiredPass.