[LLVMdev] Tablegen binary literals

[Pete Cooper]

Hi all

Currently tablegen parses binary literals such as 0b011 and immediately turns them in to integers internally.  Due to this, 0b011 is a 2-bit value because tablegen will happily drop leading zeroes on integers.

I propose that we change this, and store binary literals with a size.  I think this is much more natural, as when the user writes a value with 3 bits, I think they expect to get a value with 3 bits, and not a 2-bit value which is silently truncated and later silently zero extended.

Given this, I would then like to extend bits initializers to accept these new sized binary literals.  For example, I would like to be able to write

bits<2> opc;
bits<8> x = { opc, 0b1100, rd{1}, rs{0} }

This would let us write some encodings much more concisely, instead of having to put each initializer on its own line.

I do have patches, which I’m happy to present for review, but I’d like some feedback on the general idea before we get to the low level details.

Thanks,
Pete