[PATCH] D92479: [RISCV] remove redundant instruction when eliminate frame index

[Jessica Clarke via Phabricator via llvm-commits]

jrtc27 added inline comments.


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Comment at: llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp:174
     TII->movImm(MBB, II, DL, ScratchReg, Offset);
+    if (MI.getOpcode() == RISCV::ADDI) {
+      BuildMI(MBB, II, DL, TII->get(RISCV::ADD), MI.getOperand(0).getReg())
----------------
StephenFan wrote:
> kito-cheng wrote:
> > Just curios, does it possible get any other opcode than ADDI? below code are just update `Offset`, I guess that means we already assume it must be ADDI here? But I could be wrong since I didn't seriously tracing here before.
> > 
> > If my assumption is right then the code could be further simplified?  
> The ADDI is generated when the frameindexSDNode be selected to ADDI
> 
> ```
>   case ISD::FrameIndex: {
>     SDValue Imm = CurDAG->getTargetConstant(0, DL, XLenVT);
>     int FI = cast<FrameIndexSDNode>(Node)->getIndex();
>     SDValue TFI = CurDAG->getTargetFrameIndex(FI, VT);
>     ReplaceNode(Node, CurDAG->getMachineNode(RISCV::ADDI, DL, VT, TFI, Imm));
>     return;
>   }
> ```
> In the eliminateFrameIndex function, I think the instructions that contains the frameindex operand are
> ADDI (show above) and load/store instruction that come from loadRegFromStackSlot and storeRegToStackSlot function. 
If we had reg+reg addressing then we could fold the add into loads/stores, but given we don't I think this is the only case.


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  https://reviews.llvm.org/D92479/new/

https://reviews.llvm.org/D92479