Fix RegScavenger::forward() to work on basic blocks containing exactly

one instruction.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61236 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/RegisterScavenging.h

@@ -98,6 +98,7 @@ public:
   /// forward / backward - Move the internal MBB iterator and update register
   /// states until it has processed the specific iterator.
   void forward(MachineBasicBlock::iterator I) {
+    if (!Tracking && MBB->begin() != I) forward();
     while (MBBI != I) forward();
   }
   void backward(MachineBasicBlock::iterator I) {