[llvm] r264695 - LiveVariables: Do not remove dead flags from vreg operands

[Quentin Colombet via llvm-commits]

> On Mar 28, 2016, at 8:08 PM, Matthias Braun via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: matze
> Date: Mon Mar 28 22:08:18 2016
> New Revision: 264695
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=264695&view=rev
> Log:
> LiveVariables: Do not remove dead flags from vreg operands
> 
> Also add a FIXME comment on why Mips RDDSP causes bogus dead flags to be
> added which LiveVariables cleans up by accident.
> 
> Modified:
>    llvm/trunk/lib/CodeGen/LiveVariables.cpp
> 
> Modified: llvm/trunk/lib/CodeGen/LiveVariables.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/LiveVariables.cpp?rev=264695&r1=264694&r2=264695&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/LiveVariables.cpp (original)
> +++ llvm/trunk/lib/CodeGen/LiveVariables.cpp Mon Mar 28 22:08:18 2016
> @@ -527,9 +527,14 @@ void LiveVariables::runOnInstr(MachineIn
>         MO.setIsKill(false);
>       if (MO.readsReg())
>         UseRegs.push_back(MOReg);
> -    } else /*MO.isDef()*/ {
> -      if (!(TargetRegisterInfo::isPhysicalRegister(MOReg) &&
> -            MRI->isReserved(MOReg)))
> +    } else {
> +      assert(MO.isDef());
> +      // FIXME: We should not remove any dead flags. Howeve the MIPS RDDSP

Typo: However

> +      // instruction needs it at the moment: RDDSP gets its implicit use
> +      // operands added too late in the processing so InstrEmitter adds an
> +      // incorrect dead flag because the uses are not yet visible.

Please file a PR if not already done, to make sure we do not forget about it.

> +      if (TargetRegisterInfo::isPhysicalRegister(MOReg) &&
> +          !MRI->isReserved(MOReg))
>         MO.setIsDead(false);
>       DefRegs.push_back(MOReg);
>     }
> 
> 
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