From d3b8629a53ec5cc133e08b8e74a2b38988e78693 Mon Sep 17 00:00:00 2001
From: Andrew Trick <atrick@apple.com>
Date: Thu, 24 Jan 2013 02:09:55 +0000
Subject: [PATCH] MIsched: Added biasCriticalPath.

Allow schedulers to order DAG edges by critical path. This makes
DFS-based heuristics more stable and effective.

llvm-svn: 173317
---
 llvm/include/llvm/CodeGen/ScheduleDAG.h |  4 ++++
 llvm/lib/CodeGen/ScheduleDAG.cpp        | 15 +++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/llvm/include/llvm/CodeGen/ScheduleDAG.h b/llvm/include/llvm/CodeGen/ScheduleDAG.h
index aa91b0300ac4..9f4f66f860e7 100644
--- a/llvm/include/llvm/CodeGen/ScheduleDAG.h
+++ b/llvm/include/llvm/CodeGen/ScheduleDAG.h
@@ -455,6 +455,10 @@ namespace llvm {
       return NumSuccsLeft == 0;
     }
 
+    /// \brief Order this node's predecessor edges such that the critical path
+    /// edge occurs first.
+    void biasCriticalPath();
+
     void dump(const ScheduleDAG *G) const;
     void dumpAll(const ScheduleDAG *G) const;
     void print(raw_ostream &O, const ScheduleDAG *G) const;
diff --git a/llvm/lib/CodeGen/ScheduleDAG.cpp b/llvm/lib/CodeGen/ScheduleDAG.cpp
index e639c55a04f1..70ad94957133 100644
--- a/llvm/lib/CodeGen/ScheduleDAG.cpp
+++ b/llvm/lib/CodeGen/ScheduleDAG.cpp
@@ -301,6 +301,21 @@ void SUnit::ComputeHeight() {
   } while (!WorkList.empty());
 }
 
+void SUnit::biasCriticalPath() {
+  if (NumPreds < 2)
+    return;
+
+  SUnit::pred_iterator BestI = Preds.begin();
+  unsigned MaxDepth = BestI->getSUnit()->getDepth();
+  for (SUnit::pred_iterator
+         I = llvm::next(BestI), E = Preds.end(); I != E; ++I) {
+    if (I->getKind() == SDep::Data && I->getSUnit()->getDepth() > MaxDepth)
+      BestI = I;
+  }
+  if (BestI != Preds.begin())
+    std::swap(*Preds.begin(), *BestI);
+}
+
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 /// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or
 /// a group of nodes flagged together.