Don't try to split weird critical edges that really aren't:

BB#1: derived from LLVM BB %bb.nph28
    Live Ins: %AL
    Predecessors according to CFG: BB#0
	TEST8rr %reg16384<kill>, %reg16384, %EFLAGS<imp-def>; GR8:%reg16384
	JNE_4 <BB#2>, %EFLAGS<imp-use,kill>
	JMP_4 <BB#2>
    Successors according to CFG: BB#2 BB#2

These double CFG edges only ever occur in bugpoint-generated code, so there is
no need to attempt something clever.

llvm-svn: 117992

1 files changed, 12 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index d4f901d7933..31d12ebdc47 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -450,14 +450,24 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
   MachineFunction *MF = getParent();
   DebugLoc dl;  // FIXME: this is nowhere
 
-  // We may need to update this's terminator, but we can't do that if AnalyzeBranch
-  // fails. If this uses a jump table, we won't touch it.
+  // We may need to update this's terminator, but we can't do that if
+  // AnalyzeBranch fails. If this uses a jump table, we won't touch it.
   const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
   MachineBasicBlock *TBB = 0, *FBB = 0;
   SmallVector<MachineOperand, 4> Cond;
   if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
     return NULL;
 
+  // Avoid bugpoint weirdness: A block may end with a conditional branch but
+  // jumps to the same MBB is either case. We have duplicate CFG edges in that
+  // case that we can't handle. Since this never happens in properly optimized
+  // code, just skip those edges.
+  if (TBB && TBB == FBB) {
+    DEBUG(dbgs() << "Won't split critical edge after degenerate BB#"
+                 << getNumber() << '\n');
+    return NULL;
+  }
+
   MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
   MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
   DEBUG(dbgs() << "Splitting critical edge:"