[llvm] AArch64: Mark status flag clobbers dead in SME ABI pass (PR #228042)

[Benjamin Maxwell via llvm-commits]

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@@ -767,7 +767,8 @@ PhysRegSave MachineSMEABI::createPhysRegSave(LiveRegs PhysLiveRegs,
     RegSave.StatusFlags = MRI->createVirtualRegister(&AArch64::GPR64RegClass);
     BuildMI(MBB, MBBI, DL, TII->get(AArch64::MRS), RegSave.StatusFlags)
         .addImm(AArch64SysReg::NZCV)
-        .addReg(AArch64::NZCV, RegState::Implicit);
+        .addReg(AArch64::NZCV, RegState::Implicit)
+        .setOperandDead(2); // implicit-def $nzcv
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MacDue wrote:

I'm fairly sure MRS also does not define nzcv (here we're reading it, so this looks odd). Not sure how hard it is to fix-up this instruction though. 

https://github.com/llvm/llvm-project/pull/228042