Why can not sparcv9 backend handle i64 produced by FrameIndex?

Hi, all,

I have been recently porting a backend for our experimental DSP.
It has a regular register file for ALU, naming it R registers, and
another register file (J registers) for memory access.
Both R registers and J registers are 32-bit.

Since LLVM cannot distinguish 32-bit integers or pointers during
register allocation, I have to define J as 64-bit, although
it's physically 32-bit. This is a rude and dirty trick.
I define my TargetData as "e-p:64:64:64-i32:32:32-f32:32:32-n32".

When storing a register to stack frame, 'store' node take a FrameIndex
as an input node, where FrameIndex produces
a 64-bit operand for 'store'.
In legalization phase, llc comes into a problem saying:

    ExpandIntegerResult #0: 0xadb1888: i64 = FrameIndex<1> [ORD=2] [ID=0]
    Do not know how to expand the result of this operator!

To sovle this problem, I tried "-march=sparcv9" (LLVM 3.1 release
version), the same problem occured.
sparcv9 is a 64-bit target so FrameIndex operator produces i64 data,
and it seems v9 subtarget did not handle this well.

Then I tried llc option "-march=x86-64 -view-dag-combine1-dags". It works OK.
FrameIndex produces i64 in x86-64, but this subtarget can handle the
problem well.

So I guess hacking x86-64 backend will help me to find a solution. But
I need more clues.
Can someone tell me where to start?

Best regards.