TableGen MCInstrDesc Instruction Size Zero

Dear all,

I am trying to write an AsmParser and a CodeEmitter for simple ADD instruction.
Here is what I have in the

extern const MCInstrDesc TestInsts[] = {

{ 23, 3, 1, 0, 0, 0, 0x0ULL, nullptr, nullptr, OperandInfo13, 0, nullptr }, // Inst #23 = ADD8_rr


I parse the instruction successfully but I am not sure what I did wrong that the Size (as you can see in the line above is Zero for this instruction. (In EncodeInstruction, Desc.getSize() returns zero.)

Any help is appreciated…



Hi Sky

I think you need a ‘let Size = ‘ line in your instruction definition.

If you have fixed size instructions, then you can put a single size in the base class for all your instructions, eg, like this from

// Real instructions (have encoding information)
class EncodedI<string cstr, list pattern> : AArch64Inst<NormalFrm, cstr> {
let Pattern = pattern;
let Size = 4;

Or if you have variable sized instructions then you might need to set the size on each class of instruction you define, or even each instruction.


Thanks a lot Pete :slight_smile: