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

[Matthias Braun]

> On Jul 1, 2015, at 3:12 PM, Quentin Colombet <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).
I can change some verifiers/check functions to catch those cases earlier though. 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 :)
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.

- Matthias

> 
> Thanks,
> -Quentin
> 
>> On Jun 29, 2015, at 5:33 PM, Matthias Braun <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
>> 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
>> ==============================================================================
>> --- 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
>> ==============================================================================
>> --- 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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