Rearrange operands of the BranchInst, to be able to

access each with a fixed negative index from op_end().

This has two important implications:
- getUser() will work faster, because there are less iterations
  for the waymarking algorithm to perform. This is important
  when running various analyses that want to determine callers
  of basic blocks.
- getSuccessor() now runs faster, because the indirection via OperandList
  is not necessary: Uses corresponding to the successors are at fixed
  offset to "this".

The price we pay is the slightly more complicated logic in the operator
User::delete, as it has to pick up the information whether it has to free
the memory of an original unconditional BranchInst or a BranchInst that
was originally conditional, but has been shortened to unconditional.
I was not able to come up with a nicer solution to this problem. (And
rest assured, I tried *a lot*).

Similar reorderings will follow for InvokeInst and CallInst. After that
some optimizations to pred_iterator and CallSite will fall out naturally.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66815 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 3 insertions, 1 deletions

diff --git a/include/llvm/User.h b/include/llvm/User.h
index 1a88ce0cce..69826c0d8c 100644
--- a/include/llvm/User.h
+++ b/include/llvm/User.h
@@ -62,6 +62,7 @@ protected:
   unsigned NumOperands;
 
   void *operator new(size_t s, unsigned Us);
+  void *operator new(size_t s, unsigned Us, bool Prefix);
   User(const Type *ty, unsigned vty, Use *OpList, unsigned NumOps)
     : Value(ty, vty), OperandList(OpList), NumOperands(NumOps) {}
   Use *allocHungoffUses(unsigned) const;
@@ -74,7 +75,8 @@ protected:
   }
 public:
   ~User() {
-    Use::zap(OperandList, OperandList + NumOperands);
+    if ((intptr_t(OperandList) & 1) == 0)
+      Use::zap(OperandList, OperandList + NumOperands);
   }
   /// operator delete - free memory allocated for User and Use objects
   void operator delete(void *Usr);