ProvenanceAnalysis: Store WeakTrackingVH instead of Value* in UnderlyingValue Cache.

Summary:
Since the value stored in the cache might be deleted or replaced with
something else, we need to use tracking ValueHandlers instead of plain
Value pointers. It was discovered in one of internal builds, and
unfortunately there is no small reproducer for the issue.

The cache was introduced in rL327328.

Reviewers: ahatanak, pete

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D48407

llvm-svn: 335201

2 files changed, 7 insertions, 3 deletions

diff --git a/llvm/include/llvm/Analysis/ObjCARCAnalysisUtils.h b/llvm/include/llvm/Analysis/ObjCARCAnalysisUtils.h
index 4179544f7cf..07beb0bb60a 100644
--- a/llvm/include/llvm/Analysis/ObjCARCAnalysisUtils.h
+++ b/llvm/include/llvm/Analysis/ObjCARCAnalysisUtils.h
@@ -34,6 +34,7 @@
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
+#include "llvm/IR/ValueHandle.h"
 #include "llvm/Pass.h"
 
 namespace llvm {
@@ -89,11 +90,13 @@ inline const Value *GetUnderlyingObjCPtr(const Value *V,
 /// A wrapper for GetUnderlyingObjCPtr used for results memoization.
 inline const Value *
 GetUnderlyingObjCPtrCached(const Value *V, const DataLayout &DL,
-                           DenseMap<const Value *, const Value *> &Cache) {
+                           DenseMap<const Value *, WeakTrackingVH> &Cache) {
   if (auto InCache = Cache.lookup(V))
     return InCache;
 
-  return Cache[V] = GetUnderlyingObjCPtr(V, DL);
+  const Value *Computed = GetUnderlyingObjCPtr(V, DL);
+  Cache[V] = const_cast<Value *>(Computed);
+  return Computed;
 }
 
 /// The RCIdentity root of a value \p V is a dominating value U for which
diff --git a/llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.h b/llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.h
index 8a2e16e65fb..1276f564a02 100644
--- a/llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.h
+++ b/llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.h
@@ -28,6 +28,7 @@
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/IR/ValueHandle.h"
 #include <utility>
 
 namespace llvm {
@@ -56,7 +57,7 @@ class ProvenanceAnalysis {
 
   CachedResultsTy CachedResults;
 
-  DenseMap<const Value *, const Value *> UnderlyingObjCPtrCache;
+  DenseMap<const Value *, WeakTrackingVH> UnderlyingObjCPtrCache;
 
   bool relatedCheck(const Value *A, const Value *B, const DataLayout &DL);
   bool relatedSelect(const SelectInst *A, const Value *B);