Implement a new InvalidateStructLayoutInfo method and add some comments

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25304 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/TargetData.cpp b/lib/Target/TargetData.cpp
index 75e76fe18605989cebcc9e4bd40a3c4ba6b4a918..40b762d8e7392285fdc4b9e90ee1ae613694e8cf 100644 (file)
--- a/lib/Target/TargetData.cpp
+++ b/lib/Target/TargetData.cpp
@@ -131,6 +131,9 @@ TargetData::TargetData(const std::string &ToolName, const Module *M) {
   BoolAlignment    = 1;
 }
 
+/// Layouts - The lazy cache of structure layout information maintained by
+/// TargetData.
+///
 static std::map<std::pair<const TargetData*,const StructType*>,
                 StructLayout> *Layouts = 0;
 
@@ -165,6 +168,21 @@ const StructLayout *TargetData::getStructLayout(const StructType *Ty) const {
   }
 }
 
+/// InvalidateStructLayoutInfo - TargetData speculatively caches StructLayout
+/// objects.  If a TargetData object is alive when types are being refined and
+/// removed, this method must be called whenever a StructType is removed to
+/// avoid a dangling pointer in this cache.
+void TargetData::InvalidateStructLayoutInfo(const StructType *Ty) const {
+  if (!Layouts) return;  // No cache.
+
+  std::map<std::pair<const TargetData*,const StructType*>,
+           StructLayout>::iterator I = Layouts->find(std::make_pair(this, Ty));
+  if (I != Layouts->end())
+    Layouts->erase(I);
+}
+
+
+
 static inline void getTypeInfo(const Type *Ty, const TargetData *TD,
                                uint64_t &Size, unsigned char &Alignment) {
   assert(Ty->isSized() && "Cannot getTypeInfo() on a type that is unsized!");