[LLVMdev] Adding xadd instruction to X86

[Brent Monroe]

Hi,

I'm trying to add the xadd instruction to the X86 back end. 
xadd r/m32, r32 
exchanges r/m32 and r32, and loads the sum into r/m32.  I'm
interested in the case where the destination operand is a
memory location.

I've added the following entry to X86InstrInfo.td:
def XADD32mr  : I<0x87, MRMDestMem,
                (ops i32mem:$src1, R32:$src2),
                "xadd{l} {$src1|$src2}, {$src2|$src1}">;

The xadd is emitted for the intrinsic function:
call int (<integer type>*, <integer type>)*
%llvm.atomic_fetch_add_store(<integer type>* <pointer>,      
                                                           
<integer type> <value>)

I currently have the following code (PtrReg contains the
pointer argument, ValReg the value arg, and TmpReg an unused
register.):

addDirectMem(BuildMI(BB, X86::XADD32mr, 4,
TmpReg).addReg(TwoReg), ValReg);

This fails the assertion isMem.  Any help with this would be
appreciated.

Thanks,

Brent