[llvm-dev] Fwd: InstrEmitter::CreateVirtualRegisters handling of CopyToReg

[Friedman, Eli via llvm-dev]

I haven't had the occasion to touch this particular part of 
InstrEmitter, but the patch looks reasonable.

-Eli

On 6/8/2018 11:37 PM, Jonas Paulsson wrote:
>
> Hi,
>
> It would still be nice to get some comment about this patch which 
> seems to help on SystemZ in the case where GRX32 pseudo instructions 
> are used. This means that the register eventually ends up either in 
> GR32 or GRH32 (low or high 32 bit subregs).
>
> Basically, I wonder if anyone has tried this before and has any 
> argument against this?
>
> Thanks,
>
> Jonas
>
>
> -------- Forwarded Message --------
> Subject: 	InstrEmitter::CreateVirtualRegisters handling of CopyToReg
> Date: 	Wed, 30 May 2018 15:02:57 +0200
> From: 	Jonas Paulsson <paulsson at linux.vnet.ibm.com>
> To: 	llvm-dev <llvm-dev at lists.llvm.org>
> CC: 	Ulrich Weigand <ulrich.weigand at de.ibm.com>
>
>
>
> Hi,
>
> I wonder if anyone has any comment on a patch like:
>
> diff --git a/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
> b/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
> index 65ee3816f84..4780f6f0e59 100644
> --- a/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
> +++ b/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
> @@ -243,18 +243,21 @@ void InstrEmitter::CreateVirtualRegisters(SDNode
> *Node,
>
>       if (!VRBase && !IsClone && !IsCloned)
>         for (SDNode *User : Node->uses()) {
>           if (User->getOpcode() == ISD::CopyToReg &&
>               User->getOperand(2).getNode() == Node &&
>               User->getOperand(2).getResNo() == i) {
>             unsigned Reg =
> cast<RegisterSDNode>(User->getOperand(1))->getReg();
>             if (TargetRegisterInfo::isVirtualRegister(Reg)) {
> -            const TargetRegisterClass *RegRC = MRI->getRegClass(Reg);
> -            if (RegRC == RC) {
> +            // Allow constraining the virtual register's class within
> reason,
> +            // just like what AddRegisterOperand will allow.
> +            const TargetRegisterClass *ConstrainedRC
> +              = MRI->constrainRegClass(Reg, RC, MinRCSize);
> +            if (ConstrainedRC) {
>                 VRBase = Reg;
>                 MIB.addReg(VRBase, RegState::Define);
>                 break;
>               }
>             }
>           }
>         }
>
> Why do the register classes currently have to match exactly in this case?
>
> It seems that these COPYs that now remain may end up in the same
> register class, if the users require it. So why not constrain also here
> directly, if this is done generally when the register is used as input?
>
> /Jonas
>
>

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

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