llvm dev - Jun 2014 - [LLVMdev] Regarding Instruction definition in LLVM backend

Hi Tim,

Thank you for your response.

I need that immediate value latter to concatenate to registers' names (which
I am doing during assembly printing).

Also just Updating some status for my questioin:
I have continued with using *Defs* list. It allows me to keep Registers as
an implicit operands of /*MachineInstr*/ and later during its lowering pass
them to the /*MCInstr*/. Now seems I need only to change
*/printInstruction()/* function to Emit this instructions in appropriate
way. For that I need to change /*utils/TableGen/AsmWriterEmitter.cpp:
AsmWriterEmitter::EmitPrintInstruction*/ to generate appropriate code in
"/TARGETGenAsmWriter.inc/" file.

But I am still thinking that there should be a way to not pass the registers
as an implicit operands. So other approaches will be appreciated. 

Thanks,
Arsen



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> I need that immediate value latter to concatenate to registers' names
(which
> I am doing during assembly printing).
That really sounds like an odd implementation. Are your other
instructions more normal (i.e. proper instance of RegisterClass,
non-trivial (outs ...) and (ins ...), printing operands mostly handled
by LLVM, ...)?

If not, you really should be trying to follow that convention. This
approach just isn't going to work in LLVM. On the other hand, if they
are, what makes this MOV special? It looks like it's only that you
have a really odd intrinsic you're trying to define?

Or is it that MYREG1_NAME and MYREG2_NAME aren't your usual general
purpose registers, and actually more like system control placeholders?
AArch64, for example, has "mrs x0, TPIDR_EL0" to read the
thread-specific base address; x0 is normal, but TPIDR_EL0 isn't a
register LLVM should be tracking; it's more of an immediate with a
convenient textual form.

Either way, I think there are other ways to handle an intrinsic like
that, but we need to know more details to say what they are.

Cheers.

Tim.

Hi Tim,

Many thanks for your thoughts.

Actually I have implemented it with the approach I choose (using Defs and
then changing the assembly printer to emit the MCInstr in an appropriate
way). And seems that works for me now.

Actually I need to have finally assembly code with
 mov MYREG1_NAME_88 MYREG2_NAME_88

where 88 is an immediate argument value of the built-in function. This is
needed for my target which can understand this kind of registers.

Thank you again, Tim, for your time.
Arsen



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