[llvm-dev] Head at revision #262824 - breaks Movidius Out-of-Tree target

[Martin J. O'Riordan via llvm-dev]

Thanks Matthias,

I eventually figured that 'CompleteModel' was supposed to be on the
scheduling model and not the instruction (I grepped the other targets :-) ).

At the moment I have the dummy 'Sched<[]>' base class for my instructions, I
have added 'CompleteModel = 0' to the schedules (this also cured the COPY
problem), and 'hasNoSchedulingInfo = 1' to my pseudos and everything builds
(including libraries), so my next step will be to start the test-suite, wait
all night (I'll test on the simulator) and then see what happened.

So the dummy base 'Sched<[]>' should be unnecessary?  What is this for, and
if used properly what should be provided in the list?

My schedules specialise 'SchedMachineModel', but I have also had to extend
TableGen and the information present in the schedules to support some more
complex scheduling information than is currently supported in LLVM.  The
'ItinRW' in particular has extensions to support our architecture.

The reason for this is that I need to be able to say that the register
associated with a particular instruction operand is read or written, using a
particular port (I use 'ProcResource' for these) at a particular cycle after
the commencement of the instruction.  Most are simple and read at the
beginning of cycle-zero, and write-back at the end of the instruction (it's
natural latency), but there are some more exotic instructions that read at a
later cycle, and write-backs to registers/operands before the instruction
has completed execution (especially pipe-lined instructions), so we extended
the scheduling models to describe this.

Regarding (your previous reply on this topic):

| As of r262384 tablegen checks that it can find scheduling information
| for every instruction. So if you get the message about no information
| about instruction 'FOOBAR', can you given an example how your schedule
| information for FOOBAR looks like? Maybe there is a case missing when
| checking the old itinerary  models.
|
| In the meantime you should be easily able to set:
|
| def MyModel : SchedMachineModel {
|    // ...
|    let CompleteModel = 0;
| }

I'll have to see how to extract this is a readable form - the definitions
use a lot of multi-level 'foreach' and token pasting to construct the whole
spectrum of port dependencies, so I'll have to manually expand one.  For
example, a write operation is:

    let SchedModel = MyModel in {
        class WriteOp<int latency, ProcResourceKind resource> :
SchedWriteRes<[resource]> {
            let Latency = latency;
                let ResourceDelays = [latency];
        }
    }

A "port" might be described as:

    def 1_Latency_On_Write_Port_4 : WriteOp<1, !cast<ProcResource>("WP4")>;

Then the itinerary is a list of these, described as:

    def IT_INSN_GROUP_NAME : InstrItinClass;
    def myItin : ItinRW<[1_Latency_On_Write_Port_4, ...],
[IT_INSN_GROUP_NAME]>;

and finally:

    let Itinerary = IT_INSN_GROUP_NAME in { instructions using this
itinerary }

This is a simplification of the actual schedules, but it is structurally
accurate.

But I don't yet understand what it means to have a "complete" schedule so
that it should not be necessary for me to say:

    let CompleteModel = 0;

I certainly intend that my schedules are accurate and complete (I depend on
them), so if there is something missing then I have the potential for
erroneous scheduling.

Thanks for your help, and to Tim too, I now have it building again and will
know in a few hours if it also works.

	MartinO

-----Original Message-----
From: mbraun at apple.com [mailto:mbraun at apple.com] 
Sent: 08 March 2016 19:13
To: Martin J. O'Riordan <Martin.ORiordan at Movidius.com>
Cc: Tim Northover <t.p.northover at gmail.com>; LLVM Developers
<llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Head at revision #262824 - breaks Movidius
Out-of-Tree target


> On Mar 8, 2016, at 8:11 AM, Martin J. O'Riordan via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> 
> [I tweaked the subject, #262824 did not introduce the problem, it is just
the version I am first seeing this problem]
> 
> A quick update - I have added 'Sched<[]>' as a base class for all
instructions, and also:
This should not be necessary if you have itinerary information for your
instructions...

> 
>    let hasNoSchedulingInfo = 1;
> 
> to all the Pseudos, but while most of the errors have gone, I still get
the diagnostic for 'COPY' thus:
> 
>    error : No schedule information for instruction 'COPY'
> 
> but I don't have an instruction called COPY (this is a target-independent
default).  I also tried adding:

COPY instructions exist on any target (they are defined in
include/llvm/Target/Target.td). They definitely occur at the scheduling
phase so it makes sense to provide scheduling information for them. Usually
they are matched with InstRW expressions. The simplest form would be:

def : InstRW<[], (instrs COPY)>


> 
>    let CompleteModel = 0;
> 
> to my base instruction type, but it is unrecognised.
This needs to go into your SchedMachineModel section (it is 1 by default, so
you have to explicitely override it if you want to set it to 0).

- Matthias