From c19ef92403072daf687947dbe102ef8d469cbe89 Mon Sep 17 00:00:00 2001
From: Andrew Lenharth <andrewl@lenharth.org>
Date: Tue, 26 Sep 2006 20:02:30 +0000
Subject: [PATCH] Comments on JumpTableness

llvm-svn: 30615
---
 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp     | 1 +
 llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index c310ac7faea8..c47852b0f36a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2403,6 +2403,7 @@ const char *SDNode::getOperationName(const SelectionDAG *G) const {
   case ISD::GlobalAddress: return "GlobalAddress";
   case ISD::FrameIndex:    return "FrameIndex";
   case ISD::JumpTable:     return "JumpTable";
+  case ISD::JumpTableRelocBase: return "JumpTableRelocBase";
   case ISD::ConstantPool:  return "ConstantPool";
   case ISD::ExternalSymbol: return "ExternalSymbol";
   case ISD::INTRINSIC_WO_CHAIN: {
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 27a45a1d5227..e9fd888eadec 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -868,6 +868,9 @@ void SelectionDAGLowering::visitJumpTable(SelectionDAGISel::JumpTable &JT) {
   SDOperand LD  = DAG.getLoad(isPIC ? MVT::i32 : PTy, Copy.getValue(1), ADD,
                               DAG.getSrcValue(0));
   if (isPIC) {
+    // For Pic, the sequence is:
+    // BRIND(load(Jumptable + index) + RelocBase)
+    // RelocBase is the JumpTable on PPC and X86, GOT on Alpha
     SDOperand Reloc = DAG.getNode(ISD::JumpTableRelocBase, PTy, TAB);
     ADD = DAG.getNode(ISD::ADD, PTy,
         ((PTy != MVT::i32) ? DAG.getNode(ISD::SIGN_EXTEND, PTy, LD) : LD), Reloc);