llvm dev - Dec 2016 - Issues with DummyCGSCCPass used for IPRA

>
> Hello,
>
> I'm trying to enable interprocedural register allocation (IPRA).
Hi Maxime,

I don't understand here why you need to enable IPRA as that is already
scheduled based on option -mllvm -enable-ipra. So I think easy way to make
IPRA execute every time is to set default value of EnableIPRA option to
true.
you can find this option defined in lib/CodeGen/TargetMachine.cpp and you
may also need to change its initialization to true in  TargetOptions
constructor in include/llvm/Target/TargetOptions.h

- Vivek
> In order to do this, I’ve added the DummyCGSCCPass to our pipeline, as is
> done in TargetPassConfig::addISelPrepare. My understanding is that this
> pass wraps the following passes into an SCC pass manager, so that they are
> run in bottom-up order, which is necessary to enable register allocation
> info from callees to be available at call sites.
>
> The problem I’m running into is that we have an ImmutablePass which is run
> early in our pipeline (and needed in later machine code generation stages),
> and for some reason, this pass gets finalized and re-run multiple times,
> destroying the information we need in the process. I’m really not sure what
> is happening. The pass is clearly marked as required by later passes, but
> somehow it is found to be “dead”, finalized, and then re-run. To make
> matters more confusing, we have another ImmutablePass which is run early
> and used late, but this one doesn’t get finalized. My coworkers and I are
> really not sure what the difference might be.
>
> Could someone more familiar with IPRA or the PassManager provide some
> hints as to what might be happening?
>
> Regards,
>
> - Maxime
>
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We have our own subtarget, with its own pipeline and set of passes.

The problem I’m facing, as explained, is that adding the DummyCGSCCPass to our
pipeline causes an early pass to be finalized when it shouldn’t be. The
information then becomes unavailable when needed, in the machine code generation
part of our pipeline.

It’s unclear to us why this is happening. I was hoping someone familiar with the
pass manager may have advice, or that someone may have run into a similar
problem before.

- Maxime
> On Dec 7, 2016, at 9:46 PM, vivek pandya via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> 
> 
> Hello,
> 
> I'm trying to enable interprocedural register allocation (IPRA).
> Hi Maxime,
> 
> I don't understand here why you need to enable IPRA as that is already
scheduled based on option -mllvm -enable-ipra. So I think easy way to make IPRA
execute every time is to set default value of EnableIPRA option to true.
> you can find this option defined in lib/CodeGen/TargetMachine.cpp and you
may also need to change its initialization to true in  TargetOptions constructor
in include/llvm/Target/TargetOptions.h
> 
> - Vivek
> In order to do this, I’ve added the DummyCGSCCPass to our pipeline, as is
done in TargetPassConfig::addISelPrepare. My understanding is that this pass
wraps the following passes into an SCC pass manager, so that they are run in
bottom-up order, which is necessary to enable register allocation info from
callees to be available at call sites.
> 
> The problem I’m running into is that we have an ImmutablePass which is run
early in our pipeline (and needed in later machine code generation stages), and
for some reason, this pass gets finalized and re-run multiple times, destroying
the information we need in the process. I’m really not sure what is happening.
The pass is clearly marked as required by later passes, but somehow it is found
to be “dead”, finalized, and then re-run. To make matters more confusing, we
have another ImmutablePass which is run early and used late, but this one
doesn’t get finalized. My coworkers and I are really not sure what the
difference might be.
> 
> Could someone more familiar with IPRA or the PassManager provide some hints
as to what might be happening?
> 
> Regards,
> 
> - Maxime
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Hi,

There are two relevant hooks for you immutable pass: 

1) releaseMemory()
2) doFinalization()

Are you looking at the first one? I think you should act on the second instead
and it should solve your issue.

— 
Mehdi

> On Dec 8, 2016, at 10:58 AM, Maxime Chevalier-Boisvert via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> 
> We have our own subtarget, with its own pipeline and set of passes.
> 
> The problem I’m facing, as explained, is that adding the DummyCGSCCPass to
our pipeline causes an early pass to be finalized when it shouldn’t be. The
information then becomes unavailable when needed, in the machine code generation
part of our pipeline.
> 
> It’s unclear to us why this is happening. I was hoping someone familiar
with the pass manager may have advice, or that someone may have run into a
similar problem before.
> 
> - Maxime
> 
>> On Dec 7, 2016, at 9:46 PM, vivek pandya via llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> 
>> 
>> 
>> Hello,
>> 
>> I'm trying to enable interprocedural register allocation (IPRA).
>> Hi Maxime,
>> 
>> I don't understand here why you need to enable IPRA as that is
already scheduled based on option -mllvm -enable-ipra. So I think easy way to
make IPRA execute every time is to set default value of EnableIPRA option to
true.
>> you can find this option defined in lib/CodeGen/TargetMachine.cpp and
you may also need to change its initialization to true in  TargetOptions
constructor in include/llvm/Target/TargetOptions.h
>> 
>> - Vivek
>> In order to do this, I’ve added the DummyCGSCCPass to our pipeline, as
is done in TargetPassConfig::addISelPrepare. My understanding is that this pass
wraps the following passes into an SCC pass manager, so that they are run in
bottom-up order, which is necessary to enable register allocation info from
callees to be available at call sites.
>> 
>> The problem I’m running into is that we have an ImmutablePass which is
run early in our pipeline (and needed in later machine code generation stages),
and for some reason, this pass gets finalized and re-run multiple times,
destroying the information we need in the process. I’m really not sure what is
happening. The pass is clearly marked as required by later passes, but somehow
it is found to be “dead”, finalized, and then re-run. To make matters more
confusing, we have another ImmutablePass which is run early and used late, but
this one doesn’t get finalized. My coworkers and I are really not sure what the
difference might be.
>> 
>> Could someone more familiar with IPRA or the PassManager provide some
hints as to what might be happening?
>> 
>> Regards,
>> 
>> - Maxime
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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