llvm dev - Apr 2015 - [LLVMdev] RFC: Machine Level IR text-based serialization format

On 4/28/2015 7:13 PM, Alex L wrote:
>
>
> 2015-04-28 16:26 GMT-07:00 Matthias Braun <matze at braunis.de
> <mailto:matze at braunis.de>>:
>
>     For that use case it is worth keeping the following things in mind:
>     - Please try to keep the output of the various dump functions, esp.
>     MachineInstr::dump(), MachineOperand::dump(),
>     MachineBasicBlock::dump() as close as possible to the format you use
>     for serializing.
> [...]
>
> Ideally the new syntax would replace the existing print/dump syntax. The
> new syntax will lead to certain missing information when
> this information can be inferred (e.g. the TiedTo and IsEarlyClobber
> attributes for register operands that I mentioned earlier in this thread),
> so maybe we could have some sort of verbose dumping option where
> absolutely everything is dumped.

I think that the new syntax is less readable than the current format of 
the "dump" functions, and in the long term it would be better to have 
something more human-friendly.  However, using YAML has the advantage 
that it's easier to parse it than the direct output of "dump" and
so it
will take less time to implement a YAML-based solution.  My concern is 
that you may run out of time to complete this and the file format is not 
the most important thing in this project.  Getting it to work, if only 
as a proof of concept, would be very helpful to everyone.  Coming up 
with a fancier grammar and implementing a parser for it could be done 
later on top of the initial implementation.

-Krzysztof

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, 
hosted by The Linux Foundation

> On 2015-Apr-29, at 06:40, Krzysztof Parzyszek <kparzysz at
codeaurora.org> wrote:
> 
> On 4/28/2015 7:13 PM, Alex L wrote:
>> 
>> 
>> 2015-04-28 16:26 GMT-07:00 Matthias Braun <matze at braunis.de
>> <mailto:matze at braunis.de>>:
>> 
>>    For that use case it is worth keeping the following things in mind:
>>    - Please try to keep the output of the various dump functions, esp.
>>    MachineInstr::dump(), MachineOperand::dump(),
>>    MachineBasicBlock::dump() as close as possible to the format you use
>>    for serializing.
>> [...]
>> 
>> Ideally the new syntax would replace the existing print/dump syntax.
The
>> new syntax will lead to certain missing information when
>> this information can be inferred (e.g. the TiedTo and IsEarlyClobber
>> attributes for register operands that I mentioned earlier in this
thread),
>> so maybe we could have some sort of verbose dumping option where
>> absolutely everything is dumped.
> 
> 
> I think that the new syntax is less readable than the current format of the
"dump" functions, and in the long term it would be better to have
something more human-friendly.  However, using YAML has the advantage that
it's easier to parse it than the direct output of "dump" and so it
will take less time to implement a YAML-based solution.  My concern is that you
may run out of time to complete this and the file format is not the most
important thing in this project.  Getting it to work, if only as a proof of
concept, would be very helpful to everyone.  Coming up with a fancier grammar
and implementing a parser for it could be done later on top of the initial
implementation.
> 
> -Krzysztof
Until I got to this email, I was opposed to using YAML here -- I'd
prefer a custom grammar and parser -- but I find Krzysztof's point
here pretty convincing.

Starting with a (hybrid) YAML representation seems like a reasonable
way to bootstrap a machine IR.  Once it's in place and working, we
can come back and strip away the YAML parts until it's human-
friendly.  (And since YAML is machine-friendly, upgrade scripts for
testcases should be straightforward.)

BTW, we probably need some sort of LangRef document for this.  Maybe
docs/MIRLangRef.rst?

2015-04-29 11:40 GMT-07:00 Duncan P. N. Exon Smith <dexonsmith at
apple.com>:
>
> > On 2015-Apr-29, at 06:40, Krzysztof Parzyszek <kparzysz at
codeaurora.org>
> wrote:
> >
> > On 4/28/2015 7:13 PM, Alex L wrote:
> >>
> >>
> >> 2015-04-28 16:26 GMT-07:00 Matthias Braun <matze at braunis.de
> >> <mailto:matze at braunis.de>>:
> >>
> >>    For that use case it is worth keeping the following things in
mind:
> >>    - Please try to keep the output of the various dump functions,
esp.
> >>    MachineInstr::dump(), MachineOperand::dump(),
> >>    MachineBasicBlock::dump() as close as possible to the format
you use
> >>    for serializing.
> >> [...]
> >>
> >> Ideally the new syntax would replace the existing print/dump
syntax. The
> >> new syntax will lead to certain missing information when
> >> this information can be inferred (e.g. the TiedTo and
IsEarlyClobber
> >> attributes for register operands that I mentioned earlier in this
> thread),
> >> so maybe we could have some sort of verbose dumping option where
> >> absolutely everything is dumped.
> >
> >
> > I think that the new syntax is less readable than the current format
of
> the "dump" functions, and in the long term it would be better to
have
> something more human-friendly.  However, using YAML has the advantage that
> it's easier to parse it than the direct output of "dump" and
so it will
> take less time to implement a YAML-based solution.  My concern is that you
> may run out of time to complete this and the file format is not the most
> important thing in this project.  Getting it to work, if only as a proof of
> concept, would be very helpful to everyone.  Coming up with a fancier
> grammar and implementing a parser for it could be done later on top of the
> initial implementation.
> >
> > -Krzysztof
>
> Until I got to this email, I was opposed to using YAML here -- I'd
> prefer a custom grammar and parser -- but I find Krzysztof's point
> here pretty convincing.
>
> Starting with a (hybrid) YAML representation seems like a reasonable
> way to bootstrap a machine IR.  Once it's in place and working, we
> can come back and strip away the YAML parts until it's human-
> friendly.  (And since YAML is machine-friendly, upgrade scripts for
> testcases should be straightforward.)
>
I think that this would be a good approach.
I will work on the proposed YAML hybrid format for now and will begin
sending out the patches soon. Once it's working, people can evaluate it
for themselves and see if it suits them or if we need to change it to a
custom format.

>
> BTW, we probably need some sort of LangRef document for this.  Maybe
> docs/MIRLangRef.rst?

That's fine with me.

Alex
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