[LLVMdev] Pattern-matching a MOV instruction

[Stephen McGruer]

Dear all,

The architecture I am working with supports moving values directly from one
register to another, or moving an immediate straight to a register, and I
cannot figure out how to do this in LLVM. I originally tried matching
something like [(set RegisterClass:$dest, RegisterClass:$src)] in my
TargetInstrInfo.td:

def MOVrr : MyInstrClass<(outs CPURegs:$dest), (ins CPURegs:$src),  "mov
$dest,$src",  [(set CPURegs:$dest, CPURegs:$src)]>;

However this matches very random inputs - such as (set RegisterClass:$dest,
(or RegisterClass:$src1, RegisterClass:$src2)), which is just strange - and
is obviously not correct - for a start, it only has two operands.

How should I be pattern matching this sort of instruction? Will I have to
look into doing something with the TwoAddressInstructionPass? (
http://llvm.org/docs/CodeGenerator.html#regAlloc_twoAddr). I believe a few
of the backends have 2-operand moves, but I do not understand them at all;
X86 for example seems to match them just against the DAG pattern [], which
is... confusing, to say the least.

Any help much appreciated,
Stephen
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