Revert r70645 for now; it's causing a variety of regressions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70661 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 29 insertions, 4 deletions

diff --git a/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h
index 7dc2b94dc4..6105416a40 100644
--- a/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -25,6 +25,7 @@ namespace llvm {
 class Instruction;
 class Pass;
 class AliasAnalysis;
+class ValueDeletionListener;
 
 /// DeleteDeadBlock - Delete the specified block, which must have no
 /// predecessors.
@@ -40,8 +41,9 @@ void FoldSingleEntryPHINodes(BasicBlock *BB);
 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
 /// is dead. Also recursively delete any operands that become dead as
 /// a result. This includes tracing the def-use list from the PHI to see if
-/// it is ultimately unused or if it reaches an unused cycle.
-void DeleteDeadPHIs(BasicBlock *BB);
+/// it is ultimately unused or if it reaches an unused cycle.  If a
+/// ValueDeletionListener is specified, it is notified of the deletions.
+void DeleteDeadPHIs(BasicBlock *BB, ValueDeletionListener *VDL = 0);
 
 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
 /// if possible.  The return value indicates success or failure.
diff --git a/include/llvm/Transforms/Utils/Local.h b/include/llvm/Transforms/Utils/Local.h
index 5ea1a500c5..4cb46b0c4b 100644
--- a/include/llvm/Transforms/Utils/Local.h
+++ b/include/llvm/Transforms/Utils/Local.h
@@ -50,17 +50,40 @@ bool ConstantFoldTerminator(BasicBlock *BB);
 ///
 bool isInstructionTriviallyDead(Instruction *I);
 
+/// ValueDeletionListener - A simple abstract interface for delivering
+/// notifications when Values are deleted.
+///
+/// @todo Consider whether ValueDeletionListener can be made obsolete by
+///       requiring clients to use CallbackVH instead.
+class ValueDeletionListener {
+public:
+  /// ValueWillBeDeleted - This method is called shortly before the specified
+  /// value will be deleted.
+  virtual void ValueWillBeDeleted(Value *V) = 0;
+
+protected:
+  virtual ~ValueDeletionListener();
+};
+
 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
 /// trivially dead instruction, delete it.  If that makes any of its operands
 /// trivially dead, delete them too, recursively.
-void RecursivelyDeleteTriviallyDeadInstructions(Value *V);
+///
+/// If a ValueDeletionListener is specified, it is notified of instructions that
+/// are actually deleted (before they are actually deleted).
+void RecursivelyDeleteTriviallyDeadInstructions(Value *V,
+                                                ValueDeletionListener *VDL = 0);
 
 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
 /// dead PHI node, due to being a def-use chain of single-use nodes that
 /// either forms a cycle or is terminated by a trivially dead instruction,
 /// delete it.  If that makes any of its operands trivially dead, delete them
 /// too, recursively.
-void RecursivelyDeleteDeadPHINode(PHINode *PN);
+///
+/// If a ValueDeletionListener is specified, it is notified of instructions that
+/// are actually deleted (before they are actually deleted).
+void RecursivelyDeleteDeadPHINode(PHINode *PN,
+                                  ValueDeletionListener *VDL = 0);
 
 //===----------------------------------------------------------------------===//
 //  Control Flow Graph Restructuring.