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

3 files changed, 20 insertions, 21 deletions

diff --git a/include/llvm/Instructions.h b/include/llvm/Instructions.h
index 535333a9f5..4821155e46 100644
--- a/include/llvm/Instructions.h
+++ b/include/llvm/Instructions.h
@@ -2117,8 +2117,9 @@ DEFINE_TRANSPARENT_OPERAND_ACCESSORS(ReturnInst, Value)
 ///
 class BranchInst : public TerminatorInst {
   /// Ops list - Branches are strange.  The operands are ordered:
-  ///  TrueDest, FalseDest, Cond.  This makes some accessors faster because
-  /// they don't have to check for cond/uncond branchness.
+  ///  [Cond, FalseDest,] TrueDest.  This makes some accessors faster because
+  /// they don't have to check for cond/uncond branchness. These are mostly
+  /// accessed relative from op_end().
   BranchInst(const BranchInst &BI);
   void AssertOK();
   // BranchInst constructors (where {B, T, F} are blocks, and C is a condition):
@@ -2136,24 +2137,21 @@ class BranchInst : public TerminatorInst {
              BasicBlock *InsertAtEnd);
 public:
   static BranchInst *Create(BasicBlock *IfTrue, Instruction *InsertBefore = 0) {
-    return new(1) BranchInst(IfTrue, InsertBefore);
+    return new(1, true) BranchInst(IfTrue, InsertBefore);
   }
   static BranchInst *Create(BasicBlock *IfTrue, BasicBlock *IfFalse,
                             Value *Cond, Instruction *InsertBefore = 0) {
     return new(3) BranchInst(IfTrue, IfFalse, Cond, InsertBefore);
   }
   static BranchInst *Create(BasicBlock *IfTrue, BasicBlock *InsertAtEnd) {
-    return new(1) BranchInst(IfTrue, InsertAtEnd);
+    return new(1, true) BranchInst(IfTrue, InsertAtEnd);
   }
   static BranchInst *Create(BasicBlock *IfTrue, BasicBlock *IfFalse,
                             Value *Cond, BasicBlock *InsertAtEnd) {
     return new(3) BranchInst(IfTrue, IfFalse, Cond, InsertAtEnd);
   }
 
-  ~BranchInst() {
-    if (NumOperands == 1)
-      NumOperands = (unsigned)((Use*)this - OperandList);
-  }
+  ~BranchInst();
 
   /// Transparently provide more efficient getOperand methods.
   DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
@@ -2165,23 +2163,24 @@ public:
 
   Value *getCondition() const {
     assert(isConditional() && "Cannot get condition of an uncond branch!");
-    return getOperand(2);
+    return Op<-3>();
   }
 
   void setCondition(Value *V) {
     assert(isConditional() && "Cannot set condition of unconditional branch!");
-    setOperand(2, V);
+    Op<-3>() = V;
   }
 
   // setUnconditionalDest - Change the current branch to an unconditional branch
   // targeting the specified block.
   // FIXME: Eliminate this ugly method.
   void setUnconditionalDest(BasicBlock *Dest) {
-    Op<0>() = Dest;
+    Op<-1>() = Dest;
     if (isConditional()) {  // Convert this to an uncond branch.
-      Op<1>().set(0);
-      Op<2>().set(0);
+      Op<-2>() = 0;
+      Op<-3>() = 0;
       NumOperands = 1;
+      OperandList = op_begin();
     }
   }
 
@@ -2189,12 +2188,12 @@ public:
 
   BasicBlock *getSuccessor(unsigned i) const {
     assert(i < getNumSuccessors() && "Successor # out of range for Branch!");
-    return cast_or_null<BasicBlock>(getOperand(i));
+    return cast_or_null<BasicBlock>((&Op<-1>() - i)->get());
   }
 
   void setSuccessor(unsigned idx, BasicBlock *NewSucc) {
     assert(idx < getNumSuccessors() && "Successor # out of range for Branch!");
-    setOperand(idx, NewSucc);
+    *(&Op<-1>() - idx) = NewSucc;
   }
 
   // Methods for support type inquiry through isa, cast, and dyn_cast:
@@ -2212,11 +2211,7 @@ private:
 };
 
 template <>
-struct OperandTraits<BranchInst> : HungoffOperandTraits<> {
-  // we need to access operands via OperandList, since
-  // the NumOperands may change from 3 to 1
-  static inline void *allocate(unsigned); // FIXME
-};
+struct OperandTraits<BranchInst> : VariadicOperandTraits<1> {};
 
 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(BranchInst, Value)
 
diff --git a/include/llvm/Use.h b/include/llvm/Use.h
index a2774c802f..cde4366a5a 100644
--- a/include/llvm/Use.h
+++ b/include/llvm/Use.h
@@ -92,6 +92,8 @@ public:
   /// a User changes.
   static void zap(Use *Start, const Use *Stop, bool del = false);
 
+  /// getPrefix - Return deletable pointer if appropriate
+  Use *getPrefix();
 private:
   const Use* getImpliedUser() const;
   static Use *initTags(Use *Start, Use *Stop, ptrdiff_t Done = 0);
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);