[llvm-dev] Difficulty in Porting cloneLoop in LoopUnswitch

[raghesh via llvm-dev]

 Hi Arthur,

There are significant amounts of code that we added internally to
LoopUnswitch. I presume we will be able to move that to SimpleUnswitch, but
in the interest of time we thought of porting LoopUnswitch first.

Regards,
Raghesh
------------------------------
Raghesh Aloor
AMD India Pvt. Ltd.
Bengaluru.
------------------------------


On Thu, Apr 8, 2021 at 12:10 PM Arthur Eubanks <aeubanks at google.com> wrote:

> The new PM's equivalent of LoopUnswitch is the (not super well named)
> SimpleLoopUnswitch. Is there something specific that SimpleLoopUnswitch
> doesn't handle?
>
> On Wed, Apr 7, 2021 at 11:36 PM raghesh via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi All,
>>
>> Though the LoopUnswitch pass was not ported to the new pass manager by
>> community,  we internally at AMD are in need to do that. While doing this
>> we are facing issues to have a counterpart for the cloneLoop function, the
>> body of which is given below.
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>> *Loop *llvm::cloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
>>             LoopInfo *LI, LPPassManager *LPM) {  Loop &New =
>> *LI->AllocateLoop();  if (PL)    PL->addChildLoop(&New);  else
>> LI->addTopLevelLoop(&New);  if (LPM)    LPM->addLoop(New);  // Add all of
>> the blocks in L to the new loop.  for (Loop::block_iterator I =
>> L->block_begin(), E = L->block_end();       I != E; ++I)    if
>> (LI->getLoopFor(*I) == L)
>> New.addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);  // Add all of the
>> subloops to the new loop.  for (Loop *I : *L)    cloneLoop(I, &New, VM, LI,
>> LPM);  return &New;}*
>>
>> In the new pass manager flow, we are trying to use
>> LPMUpdater's addSiblingLoops in place of addLoop, which will be invoked
>> only for the top level loop (loop to be unswitched). According to the
>> comments given in AddSiblingLoops the loops nested inside will be traversed
>> by the pass manager anyway. In that assumption we are not adding the
>> subloops. With this we are facing assertion failures further.
>>
>> We also tried capturing all the newly created loops and adding it towards
>> the end of the LoopUnswitch pass, as done in the SimpleLoopUnswitch pass.
>> That also did not help.
>>
>> Another approach we tried is not to add the cloned loops at all to the
>> pass manager.. This worked  but not sure about its implications. We might
>> miss further optimization opportunities on these loops.
>>
>> It would be a great help if someone could point out the right way to go
>> about it.
>>
>> Regards,
>> Raghesh
>> ------------------------------
>> Raghesh Aloor
>> AMD India Pvt. Ltd.
>> Bengaluru.
>> ------------------------------
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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