Revert r100056. It was causing a failure on MSVC.

llvm-svn: 100062

1 files changed, 35 insertions, 23 deletions

diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index bd0ccb40f53..fbe4fc2f46f 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -23,7 +23,6 @@
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Assembly/Writer.h"
 #include "llvm/ADT/SmallString.h"
-#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/LeakDetector.h"
 #include "llvm/Support/raw_ostream.h"
@@ -460,41 +459,54 @@ bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
   //    conditional branch followed by an unconditional branch. DestA is the
   //    'true' destination and DestB is the 'false' destination.
 
-  bool Changed = false;
+  bool MadeChange = false;
+  bool AddedFallThrough = false;
 
   MachineFunction::iterator FallThru =
     llvm::next(MachineFunction::iterator(this));
-
-  if (DestA == 0 && DestB == 0) {
-    // Block falls through to successor.
-    DestA = FallThru;
-    DestB = FallThru;
-  } else if (DestA != 0 && DestB == 0) {
-    if (isCond)
-      // Block ends in conditional jump that falls through to successor.
+  
+  if (isCond) {
+    // If this block ends with a conditional branch that falls through to its
+    // successor, set DestB as the successor.
+    if (DestB == 0 && FallThru != getParent()->end()) {
       DestB = FallThru;
+      AddedFallThrough = true;
+    }
   } else {
-    assert(DestA && DestB && isCond &&
-           "CFG in a bad state. Cannot correct CFG edges");
+    // If this is an unconditional branch with no explicit dest, it must just be
+    // a fallthrough into DestA.
+    if (DestA == 0 && FallThru != getParent()->end()) {
+      DestA = FallThru;
+      AddedFallThrough = true;
+    }
   }
-
-  // Remove superfluous edges. I.e., those which aren't destinations of this
-  // basic block, duplicate edges, or landing pads.
-  SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
+  
   MachineBasicBlock::succ_iterator SI = succ_begin();
+  MachineBasicBlock *OrigDestA = DestA, *OrigDestB = DestB;
   while (SI != succ_end()) {
     const MachineBasicBlock *MBB = *SI;
-    if (!SeenMBBs.insert(MBB) ||
-        (MBB != DestA && MBB != DestB && !MBB->isLandingPad())) {
-      // This is a superfluous edge, remove it.
-      SI = removeSuccessor(SI);
-      Changed = true;
-    } else {
+    if (MBB == DestA) {
+      DestA = 0;
+      ++SI;
+    } else if (MBB == DestB) {
+      DestB = 0;
+      ++SI;
+    } else if (MBB->isLandingPad() && 
+               MBB != OrigDestA && MBB != OrigDestB) {
       ++SI;
+    } else {
+      // Otherwise, this is a superfluous edge, remove it.
+      SI = removeSuccessor(SI);
+      MadeChange = true;
     }
   }
 
-  return Changed;
+  if (!AddedFallThrough)
+    assert(DestA == 0 && DestB == 0 && "MachineCFG is missing edges!");
+  else if (isCond)
+    assert(DestA == 0 && "MachineCFG is missing edges!");
+
+  return MadeChange;
 }
 
 /// findDebugLoc - find the next valid DebugLoc starting at MBBI, skipping