llvm dev - Feb 2017 - Bundling MachineInstr instructions before register allocation seems to always give errors

Hello.
     I am having difficulties to bundle MachineInstr instructions, before
register
allocation (RA).
     More exactly, I registered a simple pass in addPreRegAlloc() that is trying
to create
bundles.

     I see that it is written at
http://llvm.org/docs/CodeGenerator.html#machineinstr-bundles:
       <<Packing / bundling of MachineInstr’s should be done as part of
the register
             allocation super-pass.
         More specifically, the pass which determines what MIs should be bundled
             together must be done after code generator exits SSA form (i.e.
                 after two-address pass, PHI elimination, and copy coalescing).
         Bundles should only be finalized (i.e. adding BUNDLE MIs and input and
             output register MachineOperands) after virtual registers have been
             rewritten into physical registers.
         This requirement eliminates the need to add virtual register operands
             to BUNDLE instructions which would effectively double the virtual
             register def and use lists.>>

     I presume this is the reason why I'm getting always errors after
creating bundles in
the pass registered in addPreRegAlloc().
     More exactly, my pass seems to be invoked before the "Eliminate PHI
nodes for
register allocation" pass.

     If however, there is a simple possibility to bundle MachineInstr before RA,
please
let me know.

   Thank you,
     Alex

PS: Is there a possibility to bundle MachineInstr instructions before RA and use
llvm::finalizeBundle() on these bundles in a pass invoked after RA?

In theory it should be possible. In practice you will run into issues because
nobody is really doing that right now so some things like liveness updates are
semi-broken. I am currently working on some patches myself for bundling some
things pre-ra myself. I should put up some fixes for the infrastructure
soon(ish).

- Matthias
> On Feb 23, 2017, at 6:45 AM, Alex Susu via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
>  Hello.
>    I am having difficulties to bundle MachineInstr instructions, before
register allocation (RA).
>    More exactly, I registered a simple pass in addPreRegAlloc() that is
trying to create bundles.
> 
>    I see that it is written at
http://llvm.org/docs/CodeGenerator.html#machineinstr-bundles:
>      <<Packing / bundling of MachineInstr’s should be done as part of
the register
>            allocation super-pass.
>        More specifically, the pass which determines what MIs should be
bundled
>            together must be done after code generator exits SSA form (i.e.
>                after two-address pass, PHI elimination, and copy
coalescing).
>        Bundles should only be finalized (i.e. adding BUNDLE MIs and input
and
>            output register MachineOperands) after virtual registers have
been
>            rewritten into physical registers.
>        This requirement eliminates the need to add virtual register
operands
>            to BUNDLE instructions which would effectively double the
virtual
>            register def and use lists.>>
> 
>    I presume this is the reason why I'm getting always errors after
creating bundles in the pass registered in addPreRegAlloc().
>    More exactly, my pass seems to be invoked before the "Eliminate PHI
nodes for register allocation" pass.
> 
>    If however, there is a simple possibility to bundle MachineInstr before
RA, please let me know.
> 
>  Thank you,
>    Alex
> 
> PS: Is there a possibility to bundle MachineInstr instructions before RA
and use llvm::finalizeBundle() on these bundles in a pass invoked after RA?
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

Hello.
     I come back to this more than 1 year old topic on bundles. I need to create
bundles
before register allocation to avoid generating COPY instructions in the bundle.

     Is now the bundles API more reliable - were the patches for pre-ra support
discussed
below made mainstream? I ask because, as already discussed, the solution to
avoid
generating COPY instructions, etc in a block of MachineInstr is to bundle them -
this was
discussed also at
http://lists.llvm.org/pipermail/llvm-dev/2016-October/106553.html
("spills, reloads, splits or further scheduling sneaking instruction in
between").

   Thank you,
     Alex

On 2/24/2017 6:09 AM, Matthias Braun wrote:
> In theory it should be possible. In practice you will run into issues
because nobody is
> really doing that right now so some things like liveness updates are
semi-broken. I am
> currently working on some patches myself for bundling some things pre-ra
myself. I
> should put up some fixes for the infrastructure soon(ish).
>
> - Matthias
>
>> On Feb 23, 2017, at 6:45 AM, Alex Susu via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
>>
>> Hello. I am having difficulties to bundle MachineInstr instructions,
before register
>> allocation (RA). More exactly, I registered a simple pass in
addPreRegAlloc() that is
>> trying to create bundles.
>>
>> I see that it is written at
>> http://llvm.org/docs/CodeGenerator.html#machineinstr-bundles:
<<Packing / bundling of
>> MachineInstr’s should be done as part of the register allocation
super-pass. More
>> specifically, the pass which determines what MIs should be bundled
together must be
>> done after code generator exits SSA form (i.e. after two-address pass,
PHI
>> elimination, and copy coalescing). Bundles should only be finalized
(i.e. adding
>> BUNDLE MIs and input and output register MachineOperands) after virtual
registers
>> have been rewritten into physical registers. This requirement
eliminates the need to
>> add virtual register operands to BUNDLE instructions which would
effectively double
>> the virtual register def and use lists.>>
>>
>> I presume this is the reason why I'm getting always errors after
creating bundles in
>> the pass registered in addPreRegAlloc(). More exactly, my pass seems to
be invoked
>> before the "Eliminate PHI nodes for register allocation"
pass.
>>
>> If however, there is a simple possibility to bundle MachineInstr before
RA, please
>> let me know.
>>
>> Thank you, Alex
>>
>> PS: Is there a possibility to bundle MachineInstr instructions before
RA and use
>> llvm::finalizeBundle() on these bundles in a pass invoked after RA?
>> _______________________________________________ LLVM Developers mailing
list
>> llvm-dev at lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>