[llvm-dev] Accessing TableGen defined variable in the cpp code

[Tom Stellard via llvm-dev]

On Thu, Nov 26, 2015 at 03:57:42PM +0100, Sky Flyer via llvm-dev wrote:
> Hello all,
> 
> I would like to assign some bits in the instructions, based on the order of
> mnemonics that appear in a special order. I can do it in TableGen itself,
> but it will not be well maintainable based on the things I want to
> accomplish.
> 
> Therefor, I would like to do it in the c++ file which is waaay easier (at
> least in the concept!!).
> 
> Imagine I have this in my base class in TableGen:
> 
> 
> *bits<4> bitpattern = 0;*
> *let Inst{10-7} = bitpattern;*
> 
> Then, at the moment that I am parsing the instruction, I would like to
> assign a value to "bitpattern" variable!
> for example:
> 
> ->ParseInstruction(...)
>    if (Mnemonic == "X")
>      Mnemonic = getLexer().getTok().getString();
>      if (Mnemonic == "Y")
>        *** let bitpattern = 0b1010" **  // How can I do this?*
> 
> 
> How can I do this? Is it possible?
> 

One thing you might be able to do is add 'bitpattern' as an instruction operand.
Does each instruction always have the same bitpattern?

-Tom

> Cheers,
> ES

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