[llvm] [AMDGPU][True16][CodeGen] fix v_mov_b16_t16 index in folding pass (PR #161764)

[Joe Nash via llvm-commits]

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@@ -932,7 +931,9 @@ static MachineOperand *lookUpCopyChain(const SIInstrInfo &TII,
   for (MachineInstr *SubDef = MRI.getVRegDef(SrcReg);
        SubDef && TII.isFoldableCopy(*SubDef);
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Sisyph wrote:

I haven't checked the whole call chain if this property is already checked, but we should probably check that src_modifiers are 0 on the v_mov_b16 inside isFoldableCopy. I don't think we will set them, but safer to check. That can be a separate PR.

https://github.com/llvm/llvm-project/pull/161764