llvm dev - Apr 2017 - About TableGen RangeList

Hi All,

  One thing I believe also bothers someone else. Say we have the following
code snippet:

    bits<32> insnEncoding;
    let insnEncoding{15-12} = 0b0100;

Can we write the let expression with range list like this, with the same
meaning?

    let insnEncoding{12-15} = 0b0100;

I take a look on TGParser::ParseRangePiece (lib/TableGen/TGParser.cpp),
seems the
answer is YES. Can anyone confirm this?

Thanks.

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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Okay, a little experiment shows the order matters.

  $ cat bits_4_0.td
  def basic_bits {
    bits<10> zz;
    let zz{4-0} = 0b11001;
  }

  $ llvm-tblgen bits_4_0.td
  def basic_bits {
    bits<10> zz = { ?, ?, ?, ?, ?, 1, 1, 0, 0, 1 };
    string NAME = ?;
  }

  $ cat bits_0_4.td
  def basic_bits {
    bits<10> zz;
    let zz{0-4} = 0b11001;
  }

  $ llvm-tblgen bits_4_0.td
  def basic_bits {
    bits<10> zz = { ?, ?, ?, ?, ?, 1, 0, 0, 1, 1 };
    string NAME = ?;
  }


2017-04-15 23:55 GMT+08:00 陳韋任 <chenwj.cs97g at
g2.nctu.edu.tw>:
> Hi All,
>
>   One thing I believe also bothers someone else. Say we have the following
> code snippet:
>
>     bits<32> insnEncoding;
>     let insnEncoding{15-12} = 0b0100;
>
> Can we write the let expression with range list like this, with the same
> meaning?
>
>     let insnEncoding{12-15} = 0b0100;
>
> I take a look on TGParser::ParseRangePiece (lib/TableGen/TGParser.cpp),
> seems the
> answer is YES. Can anyone confirm this?
>
> Thanks.
>
> Regards,
> chenwj
>
> --
> Wei-Ren Chen (陳韋任)
> Homepage: https://people.cs.nctu.edu.tw/~chenwj


-- 
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj

On 15 April 2017 at 19:52, 陳韋任 via llvm-dev <llvm-dev at lists.llvm.org>
wrote:
> Okay, a little experiment shows the order matters.
Interesting, thanks for reporting back. Personally I find it pretty
scary that we support the second form at all. It's mixing two
different endiannesses with no real indication of which one will win.

Tim.