Change eliminateCallFramePseudoInstr() to return an iterator

This will become necessary in a subsequent change to make this method
merge adjacent stack adjustments, i.e. it might erase the previous
and/or next instruction.

It also greatly simplifies the calls to this function from Prolog-
EpilogInserter. Previously, that had a bunch of logic to resume iteration
after the call; now it just continues with the returned iterator.

Note that this changes the behaviour of PEI a little. Previously,
it attempted to re-visit the new instruction created by
eliminateCallFramePseudoInstr(). That code was added in r36625,
but I can't see any reason for it: the new instructions will obviously
not be pseudo instructions, they will not have FrameIndex operands,
and we have already accounted for the stack adjustment.

Differential Revision: http://reviews.llvm.org/D18627

llvm-svn: 265036
diff --git a/llvm/lib/Target/NVPTX/NVPTXFrameLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXFrameLowering.cpp
index 9b34aef..48a4137 100644
--- a/llvm/lib/Target/NVPTX/NVPTXFrameLowering.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXFrameLowering.cpp
@@ -70,10 +70,10 @@
 
 // This function eliminates ADJCALLSTACKDOWN,
 // ADJCALLSTACKUP pseudo instructions
-void NVPTXFrameLowering::eliminateCallFramePseudoInstr(
+MachineBasicBlock::iterator NVPTXFrameLowering::eliminateCallFramePseudoInstr(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator I) const {
   // Simply discard ADJCALLSTACKDOWN,
   // ADJCALLSTACKUP instructions.
-  MBB.erase(I);
+  return MBB.erase(I);
 }