Add prototype for the PiNodeInserter pass

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2592 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 23 insertions, 0 deletions

diff --git a/include/llvm/Transforms/Scalar.h b/include/llvm/Transforms/Scalar.h
index ba8b90c..b649dee 100644
--- a/include/llvm/Transforms/Scalar.h
+++ b/include/llvm/Transforms/Scalar.h
@@ -98,6 +98,29 @@ 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
 // simple example of the transformation performed by this pass is:
 //