From ddde335cb79d67c46c04b2a0ffd18750b6f70e28 Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Fri, 28 Sep 2007 19:37:35 +0000
Subject: [PATCH] Remove a poor scheduling heuristic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42443 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../SelectionDAG/ScheduleDAGRRList.cpp        | 39 +++----------------
 1 file changed, 5 insertions(+), 34 deletions(-)

diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
index db5ee24e3e3..92dbb7cfd0d 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
@@ -1071,26 +1071,6 @@ static unsigned closestSucc(const SUnit *SU) {
   return MaxCycle;
 }
 
-/// calcMaxScratches - Returns an cost estimate of the worse case requirement
-/// for scratch registers. Live-in operands and live-out results don't count
-/// since they are "fixed".
-static unsigned calcMaxScratches(const SUnit *SU) {
-  unsigned Scratches = 0;
-  for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
-       I != E; ++I) {
-    if (I->isCtrl) continue;  // ignore chain preds
-    if (!I->Dep->Node || I->Dep->Node->getOpcode() != ISD::CopyFromReg)
-      Scratches++;
-  }
-  for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
-       I != E; ++I) {
-    if (I->isCtrl) continue;  // ignore chain succs
-    if (!I->Dep->Node || I->Dep->Node->getOpcode() != ISD::CopyToReg)
-      Scratches += 10;
-  }
-  return Scratches;
-}
-
 // Bottom up
 bool bu_ls_rr_sort::operator()(const SUnit *left, const SUnit *right) const {
   // There used to be a special tie breaker here that looked for
@@ -1133,23 +1113,14 @@ bool bu_ls_rr_sort::operator()(const SUnit *left, const SUnit *right) const {
     if (LDist < RDist)
       return true;
     else if (LDist == RDist) {
-      // Intuitively, it's good to push down instructions whose results are
-      // liveout so their long live ranges won't conflict with other values
-      // which are needed inside the BB. Further prioritize liveout instructions
-      // by the number of operands which are calculated within the BB.
-      unsigned LScratch = calcMaxScratches(left);
-      unsigned RScratch = calcMaxScratches(right);
-      if (LScratch > RScratch)
+      if (left->Height > right->Height)
         return true;
-      else if (LScratch == RScratch)
-        if (left->Height > right->Height)
+      else if (left->Height == right->Height)
+        if (left->Depth < right->Depth)
           return true;
-        else if (left->Height == right->Height)
-          if (left->Depth < right->Depth)
+        else if (left->Depth == right->Depth)
+          if (left->CycleBound > right->CycleBound) 
             return true;
-          else if (left->Depth == right->Depth)
-            if (left->CycleBound > right->CycleBound) 
-              return true;
     }
   }
   return false;