From a69ebdbebc9a4c53f7172bd084682b6a299594ef Mon Sep 17 00:00:00 2001
From: Dale Johannesen <dalej@apple.com>
Date: Tue, 29 May 2007 23:47:50 +0000
Subject: [PATCH] Make stable_sort in tail merging actually be stable (it never
 was, but didn't matter until my last change).  Reenable tail merging by
 default.

llvm-svn: 37354
---
 llvm/include/llvm/Target/TargetMachine.h |  4 ++--
 llvm/lib/CodeGen/BranchFolding.cpp       | 17 ++++++++++++++++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/llvm/include/llvm/Target/TargetMachine.h b/llvm/include/llvm/Target/TargetMachine.h
index 01cbe7d3106a..e7f211bf1513 100644
--- a/llvm/include/llvm/Target/TargetMachine.h
+++ b/llvm/include/llvm/Target/TargetMachine.h
@@ -187,7 +187,7 @@ public:
 
   /// getEnableTailMergeDefault - the default setting for -enable-tail-merge
   /// on this target.  User flag overrides.
-  virtual const bool getEnableTailMergeDefault() const { return false; }
+  virtual const bool getEnableTailMergeDefault() const { return true; }
 
   /// addPassesToEmitFile - Add passes to the specified pass manager to get the
   /// specified file emitted.  Typically this will involve several steps of code
@@ -322,7 +322,7 @@ public:
 
   /// getEnableTailMergeDefault - the default setting for -enable-tail-merge
   /// on this target.  User flag overrides.
-  virtual const bool getEnableTailMergeDefault() const { return false; }
+  virtual const bool getEnableTailMergeDefault() const { return true; }
 };
 
 } // End llvm namespace
diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index 1fe2962a365c..c34aeebe0ee0 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -420,6 +420,21 @@ static void FixTail(MachineBasicBlock* CurMBB, MachineBasicBlock *SuccBB,
   TII->InsertBranch(*CurMBB, SuccBB, NULL, std::vector<MachineOperand>());
 }
 
+static bool MergeCompare(std::pair<unsigned,MachineBasicBlock*> p,
+                         std::pair<unsigned,MachineBasicBlock*> q) {
+
+    if (p.first < q.first)
+      return true;
+     else if (p.first > q.first)
+      return false;
+    else if (p.second->getNumber() < q.second->getNumber())
+      return true;
+    else if (p.second->getNumber() > q.second->getNumber())
+      return false;
+    else
+      assert(0 && "Predecessor appears twice");
+}
+
 // See if any of the blocks in MergePotentials (which all have a common single
 // successor, or all have no successor) can be tail-merged.  If there is a
 // successor, any blocks in MergePotentials that are not tail-merged and
@@ -435,7 +450,7 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
   
   // Sort by hash value so that blocks with identical end sequences sort
   // together.
-  std::stable_sort(MergePotentials.begin(), MergePotentials.end());
+  std::stable_sort(MergePotentials.begin(), MergePotentials.end(), MergeCompare);
 
   // Walk through equivalence sets looking for actual exact matches.
   while (MergePotentials.size() > 1) {