Add prototype for the PiNodeInserter pass

llvm-svn: 2592

include/llvm/Transforms/Scalar.h

@@ -96,6 +96,29 @@ Pass *createIndVarSimplifyPass();
 Pass *createInstructionCombiningPass();
 
 
+//===----------------------------------------------------------------------===//
+//
+// PiNodeInsertion - This pass inserts single entry Phi nodes into basic blocks
+// that are preceeded by a conditional branch, where the branch gives
+// information about the operands of the condition.  For example, this C code:
+//   if (x == 0) { ... = x + 4;
+// becomes:
+//   if (x == 0) {
+//     x2 = phi(x);    // Node that can hold data flow information about X
+//     ... = x2 + 4;
+//
+// Since the direction of the condition branch gives information about X itself
+// (whether or not it is zero), some passes (like value numbering or ABCD) can
+// use the inserted Phi/Pi nodes as a place to attach information, in this case
+// saying that X has a value of 0 in this scope.  The power of this analysis
+// information is that "in the scope" translates to "for all uses of x2".
+//
+// This special form of Phi node is refered to as a Pi node, following the
+// terminology defined in the "Array Bounds Checks on Demand" paper.
+//
+Pass *createPiNodeInsertionPass();
+
+
 //===----------------------------------------------------------------------===//
 //
 // This pass is used to promote memory references to be register references.  A