llvm dev - Jul 2014 - [LLVMdev] [llvm]/lib/CodeGen/PrologEpilogInserter.cpp RestoreCSRegs before epilogue, why?

Hello all!
Does anybody know why "lib/CodeGen/PrologEpilogInserter.cpp" has code:
---------------------------
// Add the code to save and restore the callee saved registers
  if (!F->hasFnAttribute(Attribute::Naked))
    insertCSRSpillsAndRestores(Fn);
  .....
  if (!F->hasFnAttribute(Attribute::Naked))
    insertPrologEpilogCode(Fn);
-----------------------------
and than we use 'hacks' like this(example for MSP430(emitEpilogue,
MSP430FrameLowering.cpp) but other archs has the same code):
----------------------------
// Skip the callee-saved pop instructions.
while (MBBI != MBB.begin()) {
  MachineBasicBlock::iterator PI = prior(MBBI);
  unsigned Opc = PI->getOpcode();
  if (Opc != MSP430::POP16r && !PI->isTerminator())
    break;
  --MBBI;
}
-----------------------------
Why we don't use directly:
insertCSRSpiil
insertProlog
insertEpilog
InsertCSRRestore
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> Why we don't use directly:
> insertCSRSpiil
> insertProlog
> insertEpilog
> InsertCSRRestore
Because the world is not that simple. In particular, if you will real
MSP430FrameLowering::emitEpilogue function, you will see that it needs
to insert stuff both *before* and *after* the callee-saved spill /
restore code. In particular, we need to start to set up frame just at
the start of the function, then integrate the callee-saved spill code
as a normal frame setup and continue afterwards.

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University