[LLVMdev] MachineMemOperand and dependence information

[Akira Hatanaka]

Sorry, this is the part in ARMLoadStoreOptimizer.cpp that creates a LDRD
instruction.

         Ops.pop_back();
         Ops.pop_back();

          // Form the pair instruction.
          if (isLd) {
            MachineInstrBuilder MIB = BuildMI(*MBB, InsertPos,
                                              dl, TII->get(NewOpc))
              .addReg(EvenReg, RegState::Define)
              .addReg(OddReg, RegState::Define)
              .addReg(BaseReg);
            if (!isT2)
              MIB.addReg(OffReg);
            MIB.addImm(Offset).addImm(Pred).addReg(PredReg);
            ++NumLDRDFormed;


On Tue, Sep 7, 2010 at 1:31 PM, Bill Wendling <wendling at apple.com> wrote:

> On Sep 7, 2010, at 10:48 AM, Akira Hatanaka wrote:
>
> > I have two questions regarding MachineMemOperands and dependence
> information.
> >
> > Q1) I noticed that MachineMemOperands are lost when two LDRs are combined
> and a LDRD is generated in ARMPreAllocLoadStoreOpt:::RescheduleOps.
> >
> > (before optimization)
> > %reg1033<def> = LDR %reg1030, %reg0, 4100, pred:14, pred:%reg0;
> mem:LD4[%uglygep10]
> > %reg1054<def> = LDR %reg1030, %reg0, 4104, pred:14, pred:%reg0;
> mem:LD4[%uglygep2021]
> >
> > (after optimization)
> > %reg1054<def>, %reg1033<def> = LDRD %reg1030, %reg0, 264, pred:14,
> pred:%reg0
> >
> > Are there any reasons they need to be removed?
> > Would it break something if both MachineMemOperands were added to the
> newly generated instruction?
> >
> > (after optimization)
> > %reg1054<def>, %reg1033<def> = LDRD %reg1030, %reg0, 264, pred:14,
> pred:%reg0; mem:LD4[%uglygep10], mem:LD4[%uglygep2021]
>
> If I had to guess, I would think it's because of how LDR is defined:
>
> def addrmodepc : Operand<i32>,
>                 ComplexPattern<i32, 2, "SelectAddrModePC", []> {
>  let PrintMethod = "printAddrModePCOperand";
>  let MIOperandInfo = (ops GPR, i32imm);
> }
> def LDR  : AI2ldw<(outs GPR:$dst), (ins addrmode2:$addr), LdFrm,
> IIC_iLoadr,
>               "ldr", "\t$dst, $addr",
>               [(set GPR:$dst, (load addrmode2:$addr))]>;
>
> It's using addrmodepc, which is a ComplexPattern. The TableGen code cannot
> handle resetting the memoperands if it's dealing with a ComplexPattern.
> There's a similar bug in the X86 target.
>
> -bw
>
>
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