Fix PHIElimination optimization that uses MBB->getBasicBlock.

The BasicBlock associated with a MachineBasicBlock does not necessarily
correspond to the code in the MBB.

Don't insert a new IR BasicBlock when splitting critical edges. We are not
supposed to modify the IR during codegen, and we should be able to do just
fine with a NULL BB.

llvm-svn: 88707

1 files changed, 5 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/PHIElimination.h b/llvm/lib/CodeGen/PHIElimination.h
index edc2d36670b..94716eef6c5 100644
--- a/llvm/lib/CodeGen/PHIElimination.h
+++ b/llvm/lib/CodeGen/PHIElimination.h
@@ -110,11 +110,12 @@ namespace llvm {
     MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *A,
                                          MachineBasicBlock *B);
 
-    // FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
-    // SrcReg.  This needs to be after any def or uses of SrcReg, but before
-    // any subsequent point where control flow might jump out of the basic
-    // block.
+    /// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
+    /// SrcReg when following the CFG edge to SuccMBB. This needs to be after
+    /// any def of SrcReg, but before any subsequent point where control flow
+    /// might jump out of the basic block.
     MachineBasicBlock::iterator FindCopyInsertPoint(MachineBasicBlock &MBB,
+                                                    MachineBasicBlock &SuccMBB,
                                                     unsigned SrcReg);
 
     // SkipPHIsAndLabels - Copies need to be inserted after phi nodes and