AnalyzeBranch doesn't change which successors a bb has, just the order

we try to branch to them.

Before we were creating successor lists with duplicated entries. Fixing that
found a bug in isBlockOnlyReachableByFallthrough that would causes it to
return the wrong answer for

-----------
...
jne foo
jmp bar

foo:
----------

llvm-svn: 132882

2 files changed, 11 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 161afbafb57..1fd724f9ca7 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1925,7 +1925,7 @@ isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB) const {
     return false;
 
   // The predecessor has to be immediately before this block.
-  const MachineBasicBlock *Pred = *PI;
+  MachineBasicBlock *Pred = *PI;
 
   if (!Pred->isLayoutSuccessor(MBB))
     return false;
@@ -1934,9 +1934,16 @@ isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB) const {
   if (Pred->empty())
     return true;
 
-  // Otherwise, check the last instruction.
-  const MachineInstr &LastInst = Pred->back();
-  return !LastInst.getDesc().isBarrier();
+  // Otherwise, ask the backend.
+  const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
+  MachineBasicBlock *PredTBB = NULL, *PredFBB = NULL;
+  SmallVector<MachineOperand, 4> PredCond;
+  if (TII->AnalyzeBranch(*Pred, PredTBB, PredFBB, PredCond))
+    return false;
+
+  if (PredCond.empty())
+    return true;
+  return !PredFBB || PredFBB == MBB;
 }
 
 
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index e2016eb2d6f..b3237d5971f 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -1789,7 +1789,6 @@ bool X86InstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,
           .addMBB(UnCondBrIter->getOperand(0).getMBB());
         BuildMI(MBB, UnCondBrIter, MBB.findDebugLoc(I), get(X86::JMP_4))
           .addMBB(TargetBB);
-        MBB.addSuccessor(TargetBB);
 
         OldInst->eraseFromParent();
         UnCondBrIter->eraseFromParent();