From dae96f888124783cf2925443d9c4f30831803fae Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 7 Oct 2005 22:10:27 +0000
Subject: [PATCH] When preselecting, favor things that have low depth to select
 first.  This is faster and uses less stack space.  This reduces our stack
 requirement enough to compile sixtrack, and though it's a hack, should be
 enough until we switch to iterative isel

llvm-svn: 23664
---
 llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 10c9b2bba94a..d0059bbcd31c 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -123,6 +123,11 @@ void PPC32DAGToDAGISel::InstructionSelectBasicBlock(SelectionDAG &DAG) {
     SDOperand Node = Worklist.back();
     Worklist.pop_back();
     
+    // Chose from the least deep of the top two nodes.
+    if (!Worklist.empty() &&
+        Worklist.back().Val->getNodeDepth() < Node.Val->getNodeDepth())
+      std::swap(Worklist.back(), Node);
+    
     if ((Node.Val->getOpcode() >= ISD::BUILTIN_OP_END &&
          Node.Val->getOpcode() < PPCISD::FIRST_NUMBER) ||
         CodeGenMap.count(Node)) continue;
@@ -142,7 +147,7 @@ void PPC32DAGToDAGISel::InstructionSelectBasicBlock(SelectionDAG &DAG) {
     // Finally, legalize this node.
     Select(Node);
   }
-  
+    
   // Select target instructions for the DAG.
   DAG.setRoot(Select(DAG.getRoot()));
   CodeGenMap.clear();
@@ -1026,7 +1031,7 @@ SDOperand PPC32DAGToDAGISel::Select(SDOperand Op) {
       New = CurDAG->getNode(ISD::TokenFactor, MVT::Other, Ops);
     }
     
-    if (!N->hasOneUse()) CodeGenMap[Op] = New;
+    CodeGenMap[Op] = New;
     return New;
   }
   case ISD::CopyFromReg: {
@@ -1042,7 +1047,7 @@ SDOperand PPC32DAGToDAGISel::Select(SDOperand Op) {
     SDOperand Val = Select(N->getOperand(2));
     SDOperand New = CurDAG->getNode(ISD::CopyToReg, MVT::Other,
                                     Chain, Reg, Val);
-    if (!N->hasOneUse()) CodeGenMap[Op] = New;
+    CodeGenMap[Op] = New;
     return New;
   }
   case ISD::UNDEF:
@@ -1354,7 +1359,6 @@ SDOperand PPC32DAGToDAGISel::Select(SDOperand Op) {
                          Select(N->getOperand(0)));
     return SDOperand(N, 0);
   }
-
   case ISD::LOAD:
   case ISD::EXTLOAD:
   case ISD::ZEXTLOAD:
@@ -1402,7 +1406,6 @@ SDOperand PPC32DAGToDAGISel::Select(SDOperand Op) {
         return Ext;
     }
   }
-
   case ISD::TRUNCSTORE:
   case ISD::STORE: {
     SDOperand AddrOp1, AddrOp2;