[llvm] r241027 - RegisterCoalescer: Cleanup empty subranges after shrinkToUses()

Thu Jul 16 11:56:23 PDT 2015

I improved things in r242431.

- Matthias

> On Jul 16, 2015, at 10:37 AM, Quentin Colombet <qcolombet at apple.com> wrote:
> 
> Ping!
> 
> On the highlighted points, look for ##
> 
>> On Jul 1, 2015, at 4:04 PM, Quentin Colombet <qcolombet at apple.com <mailto:qcolombet at apple.com>> wrote:
>> 
>>> 
>>> On Jul 1, 2015, at 3:36 PM, Matthias Braun <matze at braunis.de <mailto:matze at braunis.de>> wrote:
>>> 
>>> 
>>>> On Jul 1, 2015, at 3:12 PM, Quentin Colombet <qcolombet at apple.com <mailto:qcolombet at apple.com>> wrote:
>>>> 
>>>> Hi Matthias,
>>>> 
>>>> Is there a way we can do that as part of shrinkToUses?
>>>> My concern is that future users of that API may have similar problems and would need a similar fix.
>>> The problem is that these shrinkToUses variants work on a single SubRange, but in the context of a subrange you can't just remove yourself from the list (or you'll very likely invalidate the iterators of people calling the function).
>> 
>> That’s right. I was thinking that we could return a boolean in that case, but that would be inconsistent with the meaning of the boolean for the non-specialized version of shrinkToUses.
>> 
>> I am wondering if we should return via an output parameter (like the dead definition) the empty subrange.
> 
> ## Anyway, we could add a comment on the method to point out that it might generate empty subranges and that those must be cleaned up.
> 
>> 
>>> I can change some verifiers/check functions to catch those cases earlier though.
>> 
> 
> ## A check in the verifier would be nice indeed!
> 
> Thanks,
> -Quentin
>> 
>>> It's probably also possible to loosen the requirements and allow empty subranges but that needs a careful code review.
>>> 
>>>> 
>>>> Also, could you check that we generate something meaningful, not just don’t crash (I know we already have this discussion, I still don’t like test case with FileCheck :)).
>>> I'm pretty sure you meant "without" here :)
>> 
>> Indeed :).
>> 
>>> I've added some FileCheck there now, but I can't help you with the "meaningful" part because I don't know enough about AMDGPU to judge that, it's just testing for a fixed output now.
>> 
>> That’s good enough for me.
>> 
>> Thanks,
>> -Quentin
>>> 
>>> - Matthias
>>> 
>>>> 
>>>> Thanks,
>>>> -Quentin
>>>> 
>>>>> On Jun 29, 2015, at 5:33 PM, Matthias Braun <matze at braunis.de <mailto:matze at braunis.de>> wrote:
>>>>> 
>>>>> Author: matze
>>>>> Date: Mon Jun 29 19:33:44 2015
>>>>> New Revision: 241027
>>>>> 
>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=241027&view=rev <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D241027-26view-3Drev&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=pCcxCKfF2PXt8TiSX5s8Ta-Wnhb2pKT_sldhGZ9NGD4&s=bdHrjCMa5HP0Il4M8ZeICCb7FggLodM0dWuFB16JN1g&e=>
>>>>> Log:
>>>>> RegisterCoalescer: Cleanup empty subranges after shrinkToUses()
>>>>> 
>>>>> A call to removeEmptySubranges() is necessary after every operation that
>>>>> potentially removes all segments from a subregister range; this case in
>>>>> the register coalescer was missing.
>>>>> 
>>>>> Added:
>>>>> llvm/trunk/test/CodeGen/AMDGPU/subreg-coalescer-undef-use.ll
>>>>> Modified:
>>>>> llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
>>>>> 
>>>>> Modified: llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
>>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp?rev=241027&r1=241026&r2=241027&view=diff <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_CodeGen_RegisterCoalescer.cpp-3Frev-3D241027-26r1-3D241026-26r2-3D241027-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=pCcxCKfF2PXt8TiSX5s8Ta-Wnhb2pKT_sldhGZ9NGD4&s=DfXdw403uIKq4O24cYCW9eoorJXzmyzqlvSEtv0uL3k&e=>
>>>>> ==============================================================================
>>>>> --- llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp (original)
>>>>> +++ llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp Mon Jun 29 19:33:44 2015
>>>>> @@ -1449,6 +1449,7 @@ bool RegisterCoalescer::joinCopy(Machine
>>>>>                 << format("%04X", S.LaneMask) << ")\n");
>>>>>    LIS->shrinkToUses(S, LI.reg);
>>>>>  }
>>>>> +    LI.removeEmptySubRanges();
>>>>> }
>>>>> if (ShrinkMainRange) {
>>>>>  LiveInterval &LI = LIS->getInterval(CP.getDstReg());
>>>>> 
>>>>> Added: llvm/trunk/test/CodeGen/AMDGPU/subreg-coalescer-undef-use.ll
>>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AMDGPU/subreg-coalescer-undef-use.ll?rev=241027&view=auto <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_CodeGen_AMDGPU_subreg-2Dcoalescer-2Dundef-2Duse.ll-3Frev-3D241027-26view-3Dauto&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=pCcxCKfF2PXt8TiSX5s8Ta-Wnhb2pKT_sldhGZ9NGD4&s=AaVYqE4fF_EZFC5XsYzkpZ6gbqPhRaWV6L9bq1FjSyM&e=>
>>>>> ==============================================================================
>>>>> --- llvm/trunk/test/CodeGen/AMDGPU/subreg-coalescer-undef-use.ll (added)
>>>>> +++ llvm/trunk/test/CodeGen/AMDGPU/subreg-coalescer-undef-use.ll Mon Jun 29 19:33:44 2015
>>>>> @@ -0,0 +1,20 @@
>>>>> +; RUN: llc -march=amdgcn -mcpu=SI -o /dev/null %s
>>>>> +; Don't crash when the use of an undefined value is only detected by the
>>>>> +; register coalescer because it is hidden with subregister insert/extract.
>>>>> +target triple="amdgcn--"
>>>>> +
>>>>> +define void @foobar(float %a0, float %a1, float addrspace(1)* %out) nounwind {
>>>>> +entry:
>>>>> +  %v0 = insertelement <4 x float> undef, float %a0, i32 0
>>>>> +  br i1 undef, label %ift, label %ife
>>>>> +
>>>>> +ift:
>>>>> +  %v1 = insertelement <4 x float> undef, float %a1, i32 0
>>>>> +  br label %ife
>>>>> +
>>>>> +ife:
>>>>> +  %val = phi <4 x float> [ %v1, %ift ], [ %v0, %entry ]
>>>>> +  %v2 = extractelement <4 x float> %val, i32 1
>>>>> +  store float %v2, float addrspace(1)* %out, align 4
>>>>> +  ret void
>>>>> +}
>>>>> 
>>>>> 
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