llvm dev - Jun 2020 - tablegen generated enums in tablegen

I'd like to store a tablegen generated enumeration in a record field/value.
Clearly this enumeration isn't available yet so it seems that a code
fragment should be the escape mechanism I need. Looking at the other
backends for examples, I see things like

    [{ return Imm >= 0 && Imm < 64; }]               // promising
    code Requires = [{ {} }];                                 // this looks
like a string
    let Requires = [{ {AArch64::FeatureETE} }].  // which is not promising

So I think that this would look something like:

    int reg_index           = -1;
    ...
    let reg_index = [{ return XX::R8; }];               // or
    let reg_index = [{ {XX::R8} }];

However, then I get errors of the form:

    error: Value 'reg_index' of type 'int' is incompatible with
initializer
'[{ {XX::R8} }]' of type 'code'
    error: Value 'reg_index' of type 'int' is incompatible with
initializer
'[{ return XX::R8; }]' of type 'code'

Is there a way of doing this? I don't understand TableGen casting but is
that necessary?
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I figured out the answer to my problem. I use const MCInstrDesc  desc
MCII->get(x) to get the same information. It's just that I was writing
TableGen descriptions and so I thought the answer would be in TableGen.

On Sat, Jun 27, 2020 at 10:49 AM Chris Sears <chris.sears at gmail.com>
wrote:
> I'd like to store a tablegen generated enumeration in a record
> field/value. Clearly this enumeration isn't available yet so it seems
that
> a code fragment should be the escape mechanism I need. Looking at the other
> backends for examples, I see things like
>
>     [{ return Imm >= 0 && Imm < 64; }]               //
promising
>     code Requires = [{ {} }];                                 // this looks
> like a string
>     let Requires = [{ {AArch64::FeatureETE} }].  // which is not promising
>
> So I think that this would look something like:
>
>     int reg_index           = -1;
>     ...
>     let reg_index = [{ return XX::R8; }];               // or
>     let reg_index = [{ {XX::R8} }];
>
> However, then I get errors of the form:
>
>     error: Value 'reg_index' of type 'int' is incompatible
with
> initializer '[{ {XX::R8} }]' of type 'code'
>     error: Value 'reg_index' of type 'int' is incompatible
with
> initializer '[{ return XX::R8; }]' of type 'code'
>
> Is there a way of doing this? I don't understand TableGen casting but
is
> that necessary?
>

-- 
Ite Ursi
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Hi Chris,

On Sun, Jun 28, 2020 at 9:37 AM Chris Sears via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> I'd like to store a tablegen generated enumeration in a record
field/value. Clearly this enumeration isn't available yet so it seems that a
code fragment should be the escape mechanism I need.
I don't think this is clear at all. Maybe you can explain what you're
trying to do and why simply using the enumeration fails?

[snip]
> So I think that this would look something like:
>
>     int reg_index           = -1;
>     ...
>     let reg_index = [{ return XX::R8; }];               // or
>     let reg_index = [{ {XX::R8} }];
>
> However, then I get errors of the form:
>
>     error: Value 'reg_index' of type 'int' is incompatible
with initializer '[{ {XX::R8} }]' of type 'code'
>     error: Value 'reg_index' of type 'int' is incompatible
with initializer '[{ return XX::R8; }]' of type 'code'
Well, yes. [{ }] is really just more convenient syntax for strings
that are meant to contain code snippets, and you can't assign a string
to an integer :) Those code snippets aren't executed by TableGen,
they're pasted into TableGen-generated C++ and only executed at
runtime.

Why doesn't

    let reg_index = R8;

or whatever work, if R8 is an object known to TableGen?

Cheers,
Nicolai

>
> Is there a way of doing this? I don't understand TableGen casting but
is that necessary?
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev


-- 
Lerne, wie die Welt wirklich ist,
aber vergiss niemals, wie sie sein sollte.

As a generic note, I don't believe that there are many places within 
TableGen's set of code generators that handle 'code' values as 
pass-through in the way you hint at below. One place that does is 
SearchableTable/GenericTable field values, and that is pretty useful.

  -Hal

On 6/28/20 11:06 AM, Chris Sears via llvm-dev wrote:
> I figured out the answer to my problem. I use const MCInstrDesc  desc 
> = MCII->get(x) to get the same information. It's just that I was 
> writing TableGen descriptions and so I thought the answer would be in 
> TableGen.
>
> On Sat, Jun 27, 2020 at 10:49 AM Chris Sears <chris.sears at gmail.com 
> <mailto:chris.sears at gmail.com>> wrote:
>
>     I'd like to store a tablegen generated enumeration in a record
>     field/value. Clearly this enumeration isn't available yet so it
>     seems that a code fragment should be the escape mechanism I need.
>     Looking at the other backends for examples, I see things like
>
>     [{ return Imm >= 0 && Imm < 64; }] // promising
>     code Requires = [{ {} }];                                 // this
>     looks like a string
>     let Requires = [{ {AArch64::FeatureETE} }].  // which is not promising
>
>     So I thinkthat this would look something like:
>
>     int reg_index           = -1;
>         ...
>     let reg_index = [{ return XX::R8; }];   // or
>     let reg_index = [{ {XX::R8} }];
>
>     However, thenIget errors of the form:
>
>     error: Value 'reg_index' of type 'int' is incompatible
with
>     initializer '[{ {XX::R8} }]' of type 'code'
>     error: Value 'reg_index' of type 'int' is incompatible
with
>     initializer '[{ return XX::R8; }]' of type 'code'
>
>     Is there a way of doing this? I don't understand TableGen casting
>     but is that necessary?
>
>
>
> -- 
> Ite Ursi
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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