Fix use-after-free bug in AffectedValueCallbackVH::allUsesReplacedWith

When transferring affected values in the cache from an old value, identified by
the value of the current callback, to the specified new value we might need to
insert a new entry into the DenseMap which constitutes the cache. Doing so
might delete the current callback object. Move the copying logic into a new
function, a member of the assumption cache itself, so that we don't run into UB
should the callback handle itself be removed mid-copy.

Differential Revision: https://reviews.llvm.org/D28749

llvm-svn: 292133

1 files changed, 17 insertions, 10 deletions

diff --git a/llvm/lib/Analysis/AssumptionCache.cpp b/llvm/lib/Analysis/AssumptionCache.cpp
index aa55d79b761..5851594700a 100644
--- a/llvm/lib/Analysis/AssumptionCache.cpp
+++ b/llvm/lib/Analysis/AssumptionCache.cpp
@@ -24,7 +24,7 @@
 using namespace llvm;
 using namespace llvm::PatternMatch;
 
-SmallVector<WeakVH, 1> &AssumptionCache::getAffectedValues(Value *V) {
+SmallVector<WeakVH, 1> &AssumptionCache::getOrInsertAffectedValues(Value *V) {
   // Try using find_as first to avoid creating extra value handles just for the
   // purpose of doing the lookup.
   auto AVI = AffectedValues.find_as(V);
@@ -98,7 +98,7 @@ void AssumptionCache::updateAffectedValues(CallInst *CI) {
   }
 
   for (auto &AV : Affected) {
-    auto &AVV = getAffectedValues(AV);
+    auto &AVV = getOrInsertAffectedValues(AV);
     if (std::find(AVV.begin(), AVV.end(), CI) == AVV.end())
       AVV.push_back(CI);
   }
@@ -111,20 +111,27 @@ void AssumptionCache::AffectedValueCallbackVH::deleted() {
   // 'this' now dangles!
 }
 
+void AssumptionCache::copyAffectedValuesInCache(Value *OV, Value *NV) {
+  auto &NAVV = getOrInsertAffectedValues(NV);
+  auto AVI = AffectedValues.find(OV);
+  if (AVI == AffectedValues.end())
+    return;
+
+  for (auto &A : AVI->second)
+    if (std::find(NAVV.begin(), NAVV.end(), A) == NAVV.end())
+      NAVV.push_back(A);
+}
+
 void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
   if (!isa<Instruction>(NV) && !isa<Argument>(NV))
     return;
 
   // Any assumptions that affected this value now affect the new value.
 
-  auto &NAVV = AC->getAffectedValues(NV);
-  auto AVI = AC->AffectedValues.find(getValPtr());
-  if (AVI == AC->AffectedValues.end())
-    return;
-
-  for (auto &A : AVI->second)
-    if (std::find(NAVV.begin(), NAVV.end(), A) == NAVV.end())
-      NAVV.push_back(A);
+  AC->copyAffectedValuesInCache(getValPtr(), NV);
+  // 'this' now might dangle! If the AffectedValues map was resized to add an
+  // entry for NV then this object might have been destroyed in favor of some
+  // copy in the grown map.
 }
 
 void AssumptionCache::scanFunction() {