Add two new classes: WeakVH and AssertingVH. These are both "ValueHandles",

which are effectively smart pointers to Value*'s.  They are both very light
weight and simple, and react to values being destroyed or being RAUW'd.

WeakVN does a best effort to follow a value around, including through RAUW 
operations and will get nulled out of the value is destroyed.  This is useful
for the eventual "metadata that references a value" work, because it is a
reference to a value that does not show up on its use_* list.

AssertingVH is a pointer that compiles down to a dumb raw pointer when 
assertions are disabled.  When enabled, it emits an assertion if the 
pointed-to value is destroyed while it is still being referenced.  This
is very useful for Maps and other things, and should have caught the recent
bugs in CallGraph and Reassociate, for example.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68149 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 217 insertions, 0 deletions

diff --git a/include/llvm/Support/ValueHandle.h b/include/llvm/Support/ValueHandle.h
new file mode 100644
index 0000000000..0494b27019
--- /dev/null
+++ b/include/llvm/Support/ValueHandle.h
@@ -0,0 +1,217 @@
+//===- llvm/Support/ValueHandle.h - Value Smart Pointer classes -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the ValueHandle class and its sub-classes.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_VALUEHANDLE_H
+#define LLVM_SUPPORT_VALUEHANDLE_H
+
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/Value.h"
+
+namespace llvm {
+
+/// ValueHandleBase - This is the common base class of value handles.
+/// ValueHandle's are smart pointers to Value's that have special behavior when
+/// the value is deleted or ReplaceAllUsesWith'd.  See the specific handles
+/// below for details.
+///
+class ValueHandleBase {
+  friend class Value;
+protected:
+  /// HandleBaseKind - This indicates what base class the handle actually is.
+  /// This is to avoid having a vtable for the light-weight handle pointers. The
+  /// fully generally Callback version does have a vtable.
+  enum HandleBaseKind {
+    Assert,
+    Weak,
+    Callback
+  };
+private:
+  
+  PointerIntPair<ValueHandleBase**, 2, HandleBaseKind> PrevPair;
+  ValueHandleBase *Next;
+  Value *VP;
+public:
+  ValueHandleBase(HandleBaseKind Kind) : PrevPair(0, Kind), Next(0), VP(0) {}
+  ValueHandleBase(HandleBaseKind Kind, Value *V)
+    : PrevPair(0, Kind), Next(0), VP(V) {
+    if (V)
+      AddToUseList();
+  }
+  ValueHandleBase(HandleBaseKind Kind, const ValueHandleBase &RHS)
+    : PrevPair(0, Kind), Next(0), VP(RHS.VP) {
+    if (VP)
+      AddToExistingUseList(RHS.getPrevPtr());
+  }
+  ~ValueHandleBase() {
+    if (VP)
+      RemoveFromUseList();   
+  }
+  
+  Value *operator=(Value *RHS) {
+    if (VP == RHS) return RHS;
+    if (VP) RemoveFromUseList();
+    VP = RHS;
+    if (VP) AddToUseList();
+    return RHS;
+  }
+
+  Value *operator=(const ValueHandleBase &RHS) {
+    if (VP == RHS.VP) return RHS.VP;
+    if (VP) RemoveFromUseList();
+    VP = RHS.VP;
+    if (VP) AddToExistingUseList(RHS.getPrevPtr());
+    return VP;
+  }
+  
+  Value *operator->() const { return getValPtr(); }
+  Value &operator*() const { return *getValPtr(); }
+  
+  bool operator==(const Value *RHS) const { return VP == RHS; }
+  bool operator==(const ValueHandleBase &RHS) const { return VP == RHS.VP; }
+  bool operator!=(const Value *RHS) const { return VP != RHS; }
+  bool operator!=(const ValueHandleBase &RHS) const { return VP != RHS.VP; }
+  bool operator<(const Value *RHS) const { return VP < RHS; }
+  bool operator<(const ValueHandleBase &RHS) const { return VP < RHS.VP; }
+  bool operator>(const Value *RHS) const { return VP > RHS; }
+  bool operator>(const ValueHandleBase &RHS) const { return VP > RHS.VP; }
+  bool operator<=(const Value *RHS) const { return VP <= RHS; }
+  bool operator<=(const ValueHandleBase &RHS) const { return VP <= RHS.VP; }
+  bool operator>=(const Value *RHS) const { return VP >= RHS; }
+  bool operator>=(const ValueHandleBase &RHS) const { return VP >= RHS.VP; }
+  
+protected:
+  Value *getValPtr() const { return VP; }
+private:
+  // Callbacks made from Value.
+  static void ValueIsDeleted(Value *V);
+  static void ValueIsRAUWd(Value *Old, Value *New);
+  
+  // Internal implementation details.
+  ValueHandleBase **getPrevPtr() const { return PrevPair.getPointer(); }
+  HandleBaseKind getKind() const { return PrevPair.getInt(); }
+  void setPrevPtr(ValueHandleBase **Ptr) { PrevPair.setPointer(Ptr); }
+  
+  /// AddToUseList - Add this ValueHandle to the use list for VP, where List is
+  /// known to point into the existing use list.
+  void AddToExistingUseList(ValueHandleBase **List);
+  
+  /// AddToUseList - Add this ValueHandle to the use list for VP.
+  void AddToUseList();
+  /// RemoveFromUseList - Remove this ValueHandle from its current use list.
+  void RemoveFromUseList();
+};
+  
+/// WeakVH - This is a value handle that tries hard to point to a Value, even
+/// across RAUW operations, but will null itself out if the value is destroyed.
+/// this is useful for advisory sorts of information, but should not be used as
+/// the key of a map (since the map would have to rearrange itself when the
+/// pointer changes).
+class WeakVH : public ValueHandleBase {
+public:
+  WeakVH() : ValueHandleBase(Weak) {}
+  WeakVH(Value *P) : ValueHandleBase(Weak, P) {}
+  WeakVH(const WeakVH &RHS)
+    : ValueHandleBase(Weak, RHS) {}
+
+};  
+  
+/// AssertingVH - This is a Value Handle that points to a value and asserts out
+/// if the value is destroyed while the handle is still live.  This is very
+/// useful for catching dangling pointer bugs and other things which can be
+/// non-obvious.  One particularly useful place to use this is as the Key of a
+/// map.  Dangling pointer bugs often lead to really subtle bugs that only occur
+/// if another object happens to get allocated to the same address as the old
+/// one.  Using an AssertingVH ensures that an assert is triggered as soon as
+/// the bad delete occurs.
+///
+/// Note that an AssertingVH handle does *not* follow values across RAUW
+/// operations.  This means that RAUW's need to explicitly update the
+/// AssertingVH's as it moves.  This is required because in non-assert mode this
+  /// class turns into a trivial wrapper around a pointer.
+template <typename ValueTy = Value>
+class AssertingVH 
+#ifndef NDEBUG
+  : public ValueHandleBase
+#endif
+  {
+
+#ifndef NDEBUG
+  ValueTy *getValPtr() const {
+    return static_cast<ValueTy*>(ValueHandleBase::getValPtr());
+  }
+  void setValPtr(ValueTy *P) {
+    ValueHandleBase::operator=(P);
+  }
+#else
+  ValueTy *ThePtr;
+  ValueTy *getValPtr() const { return ThePtr; }
+  void setValPtr(ValueTy *P) { ThePtr = P; }
+#endif
+
+public:
+#ifndef NDEBUG
+  AssertingVH() : ValueHandleBase(Assert) {}
+  AssertingVH(ValueTy *P) : ValueHandleBase(Assert, P) {}
+  AssertingVH(const AssertingVH &RHS) : ValueHandleBase(Assert, RHS) {}
+#else
+  AssertingVH() : ThePtr(0) {}
+  AssertingVH(ValueTy *P) : ThePtr(P) {}
+#endif
+
+  operator ValueTy*() const {
+    return getValPtr();
+  }
+
+  ValueTy *operator=(ValueTy *RHS) {
+    setValPtr(RHS);
+    return getValPtr();
+  }
+  ValueTy *operator=(AssertingVH<ValueTy> &RHS) {
+    setValPtr(RHS.getValPtr());
+    return getValPtr();
+  }
+
+  ValueTy *operator->() const { return getValPtr(); }
+  ValueTy &operator*() const { return getValPtr(); }
+
+  // Duplicate these from the base class so that they work when assertions are
+  // off.
+  bool operator==(const Value *RHS) const { return getValPtr() == RHS; }
+  bool operator!=(const Value *RHS) const { return getValPtr() != RHS; }
+  bool operator<(const Value *RHS) const { return getValPtr() < RHS; }
+  bool operator>(const Value *RHS) const { return getValPtr() > RHS; }
+  bool operator<=(const Value *RHS) const { return getValPtr() <= RHS; }
+  bool operator>=(const Value *RHS) const { return getValPtr() >= RHS; }
+  bool operator==(const AssertingVH &RHS) const {
+    return getValPtr() == RHS.getValPtr();
+  }
+  bool operator!=(const AssertingVH &RHS) const {
+    return getValPtr() != RHS.getValPtr();
+  }
+  bool operator<(const AssertingVH &RHS) const {
+    return getValPtr() < RHS.getValPtr();
+  }
+  bool operator>(const AssertingVH &RHS) const {
+    return getValPtr() > RHS.getValPtr();
+  }
+  bool operator<=(const AssertingVH &RHS) const {
+    return getValPtr() <= RHS.getValPtr();
+  }
+  bool operator>=(const AssertingVH &RHS) const {
+    return getValPtr() >= RHS.getValPtr();
+  }
+};
+
+} // End llvm namespace
+
+#endif