[llvm] r323369 - [GlobalISel] Don't fall back to FastISel.

[Quentin Colombet via llvm-commits]

Oh I missed Gerolf replied on that thread.
I am fine with that change if that’s what people want, my concern is that we will degrade potentially the compile time on fallback path even more.

> Le 24 janv. 2018 à 13:59, Amara Emerson <aemerson at apple.com> a écrit :
> 
>> On 24 Jan 2018, at 21:18, Quentin Colombet <qcolombet at apple.com> wrote:
>> 
>> Hi Amara,
>> 
>> Falling back to FastISel was intended to get the best performance from the fallback path.
>> 
>> Why are we doing this change now?
>> 
>> Cheers,
>> -Quentin
>> 
>>> On Jan 24, 2018, at 11:59 AM, Amara Emerson via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>>> 
>>> Author: aemerson
>>> Date: Wed Jan 24 11:59:29 2018
>>> New Revision: 323369
>>> 
>>> URL: http://llvm.org/viewvc/llvm-project?rev=323369&view=rev
>>> Log:
>>> [GlobalISel] Don't fall back to FastISel.
>>> 
>>> Apparently checking the pass structure isn't enough to ensure that we don't fall
>>> back to FastISel, as it's set up as part of the SelectionDAGISel.
>>> 
>>> Added:
>>>   llvm/trunk/test/CodeGen/AArch64/GlobalISel/fallback-nofastisel.ll
>>> Modified:
>>>   llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
>>>   llvm/trunk/lib/CodeGen/TargetPassConfig.cpp
>>> 
>>> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp?rev=323369&r1=323368&r2=323369&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp (original)
>>> +++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp Wed Jan 24 11:59:29 2018
>>> @@ -1380,8 +1380,10 @@ void SelectionDAGISel::SelectAllBasicBlo
>>>  FastISelFailed = false;
>>>  // Initialize the Fast-ISel state, if needed.
>>>  FastISel *FastIS = nullptr;
>>> -  if (TM.Options.EnableFastISel)
>>> +  if (TM.Options.EnableFastISel) {
>>> +    DEBUG(dbgs() << "Enabling fast-isel\n");
>>>    FastIS = TLI->createFastISel(*FuncInfo, LibInfo);
>>> +  }
>>> 
>>>  setupSwiftErrorVals(Fn, TLI, FuncInfo);
>>> 
>>> 
>>> Modified: llvm/trunk/lib/CodeGen/TargetPassConfig.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/TargetPassConfig.cpp?rev=323369&r1=323368&r2=323369&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/CodeGen/TargetPassConfig.cpp (original)
>>> +++ llvm/trunk/lib/CodeGen/TargetPassConfig.cpp Wed Jan 24 11:59:29 2018
>>> @@ -708,6 +708,8 @@ bool TargetPassConfig::addCoreISelPasses
>>>  if (EnableGlobalISelOption == cl::BOU_TRUE ||
>>>      (EnableGlobalISelOption == cl::BOU_UNSET &&
>>>       TM->Options.EnableGlobalISel && EnableFastISelOption != cl::BOU_TRUE)) {
>>> +    TM->setFastISel(false);
>>> +
>>>    if (addIRTranslator())
>>>      return true;
>>> 
>>> 
>>> Added: llvm/trunk/test/CodeGen/AArch64/GlobalISel/fallback-nofastisel.ll
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/GlobalISel/fallback-nofastisel.ll?rev=323369&view=auto
>>> ==============================================================================
>>> --- llvm/trunk/test/CodeGen/AArch64/GlobalISel/fallback-nofastisel.ll (added)
>>> +++ llvm/trunk/test/CodeGen/AArch64/GlobalISel/fallback-nofastisel.ll Wed Jan 24 11:59:29 2018
>>> @@ -0,0 +1,10 @@
>>> +; RUN: llc -mtriple=aarch64_be-- %s -o /dev/null -debug-only=isel -O0 2>&1 | FileCheck %s
>>> +
>>> +; This test uses big endian in order to force an abort since it's not currently supported for GISel.
>>> +; The purpose is to check that we don't fall back to FastISel. Checking the pass structure is insufficient
>>> +; because the FastISel is set up in the SelectionDAGISel, so it doesn't appear on the pass structure.
>>> +
>>> +; CHECK-NOT: Enabling fast-ise
>>> +define void @empty() {
>>> +  ret void
>>> +}
>>> 
>>> 
>>> _______________________________________________
>>> llvm-commits mailing list
>>> llvm-commits at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>> 
> 
> This was always the intention IIRC, Gerolf suggested it here: https://reviews.llvm.org/D41362 unless there’s some discussion I’ve missed. The existing tests with the -debug-pass=Structure option doesn’t show the difference between falling back to fast-isel and SelectionDAG.
> 
> Cheers,
> Amara
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180124/0c373d0c/attachment.html>