From aa60ddac394e8d79ecd9700e32b595c115585007 Mon Sep 17 00:00:00 2001
From: Bob Wilson <bob.wilson@apple.com>
Date: Tue, 17 Nov 2009 18:30:09 +0000
Subject: [PATCH] Remove a special case for tail merging that seems to be both
 broken and unnecessary.  It is broken because the "isIdenticalTo" check
 should be negated.  If that is fixed, this code causes the
 CodeGen/X86/tail-opts.ll test to fail, in the dont_merge_oddly function. 
 And, I confirmed that the regression is real -- the generated code is worse. 
 As far as I can tell, that tail-opts.ll test is checking for what this code
 is supposed to handle and we're doing the right thing anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89121 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/BranchFolding.cpp | 33 ---------------------------------
 1 file changed, 33 deletions(-)

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 8a6b0de4e3a..d344af06fd5 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -670,39 +670,6 @@ bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
   // this many instructions in common.
   unsigned minCommonTailLength = TailMergeSize;
 
-  // If there's a successor block, there are some cases which don't require
-  // new branching and as such are very likely to be profitable.
-  if (SuccBB) {
-    if (SuccBB->pred_size() == MergePotentials.size() &&
-        !MergePotentials[0].getBlock()->empty()) {
-      // If all the predecessors have at least one tail instruction in common,
-      // merging is very likely to be a win since it won't require an increase
-      // in static branches, and it will decrease the static instruction count.
-      bool AllPredsMatch = true;
-      MachineBasicBlock::iterator FirstNonTerm;
-      unsigned MinNumTerms = CountTerminators(MergePotentials[0].getBlock(),
-                                              FirstNonTerm);
-      if (FirstNonTerm != MergePotentials[0].getBlock()->end()) {
-        for (unsigned i = 1, e = MergePotentials.size(); i != e; ++i) {
-          MachineBasicBlock::iterator OtherFirstNonTerm;
-          unsigned NumTerms = CountTerminators(MergePotentials[0].getBlock(),
-                                               OtherFirstNonTerm);
-          if (NumTerms < MinNumTerms)
-            MinNumTerms = NumTerms;
-          if (OtherFirstNonTerm == MergePotentials[i].getBlock()->end() ||
-              OtherFirstNonTerm->isIdenticalTo(FirstNonTerm)) {
-            AllPredsMatch = false;
-            break;
-          }
-        }
-
-        // If they all have an instruction in common, do any amount of merging.
-        if (AllPredsMatch)
-          minCommonTailLength = MinNumTerms + 1;
-      }
-    }
-  }
-
   DEBUG(errs() << "\nTryTailMergeBlocks: ";
         for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
           errs() << "BB#" << MergePotentials[i].getBlock()->getNumber()