From 7dda453410eb957cd52cff4f8fa8d5a9c09e28df Mon Sep 17 00:00:00 2001
From: Dale Johannesen <dalej@apple.com>
Date: Wed, 10 Mar 2010 00:11:34 +0000
Subject: [PATCH] Speculatively revert 98104; could be what's causing crashes

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@98108 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/BranchFolding.cpp | 59 ++---------------------------------
 1 file changed, 3 insertions(+), 56 deletions(-)

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index adf1c141527..a937e8f4b43 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -347,29 +347,15 @@ static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
     --I1; --I2;
     // Skip debugging pseudos; necessary to avoid changing the code.
     while (I1->isDebugValue()) {
-      if (I1==MBB1->begin()) {
-        while (I2->isDebugValue()) {
-          if (I2==MBB2->begin())
-            // I1==DBG at begin; I2==DBG at begin
-            return TailLen;
-          --I2;
-        }
-        ++I2;
-        // I1==DBG at begin; I2==non-DBG, or first of DBGs not at begin
+      if (I1==MBB1->begin())
         return TailLen;
-      }
       --I1;
     }
-    // I1==first (untested) non-DBG preceding known match
     while (I2->isDebugValue()) {
-      if (I2==MBB2->begin()) {
-        ++I1;
-        // I1==non-DBG, or first of DBGs not at begin; I2==DBG at begin
+      if (I2==MBB2->begin())
         return TailLen;
-      }
       --I2;
     }
-    // I1, I2==first (untested) non-DBGs preceding known match
     if (!I1->isIdenticalTo(I2) ||
         // FIXME: This check is dubious. It's used to get around a problem where
         // people incorrectly expect inline asm directives to remain in the same
@@ -382,29 +368,6 @@ static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
     }
     ++TailLen;
   }
-  // Back past possible debugging pseudos at beginning of block.  This matters
-  // when one block differs from the other only by whether debugging pseudos
-  // are present at the beginning.  (This way, the various checks later for
-  // I1==MBB1->begin() work as expected.)
-  if (I1 == MBB1->begin() && I2 != MBB2->begin()) {
-    --I2;
-    while (I2->isDebugValue()) {
-      if (I2 == MBB2->begin()) {
-        return TailLen;
-        }
-      --I2;
-    }
-    ++I2;
-  }
-  if (I2 == MBB2->begin() && I1 != MBB1->begin()) {
-    --I1;
-    while (I1->isDebugValue()) {
-      if (I1 == MBB1->begin())
-        return TailLen;
-      --I1;
-    }
-    ++I1;
-  }
   return TailLen;
 }
 
@@ -1200,23 +1163,7 @@ ReoptimizeBlock:
       // be 'non-branch terminators' in the block, try removing the branch and
       // then seeing if the block is empty.
       TII->RemoveBranch(*MBB);
-      // If the only things remaining in the block are debug info, remove these
-      // as well, so this will behave the same as an empty block in non-debug
-      // mode.
-      if (!MBB->empty()) {
-        bool NonDebugInfoFound = false;
-        for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
-             I != E; ++I) {
-          if (!I->isDebugValue()) {
-            NonDebugInfoFound = true;
-            break;
-          }
-        }
-        if (!NonDebugInfoFound)
-          // Make the block empty, losing the debug info (we could probably
-          // improve this in some cases.)
-          MBB->erase(MBB->begin(), MBB->end());
-      }
+
       // If this block is just an unconditional branch to CurTBB, we can
       // usually completely eliminate the block.  The only case we cannot
       // completely eliminate the block is when the block before this one