[clang] [llvm] [AArch64][SME] Save VG for unwind info when changing streaming-mode (PR #83301)

[Kerry McLaughlin via cfe-commits]

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@@ -221,6 +224,15 @@ def : Pat<(AArch64_smstop (i32 svcr_op:$pstate), (i64 /*AArch64SME::Always*/0)),
           (MSRpstatesvcrImm1 svcr_op:$pstate, 0b0)>;
 
 
+// Pseudo to insert cfi_offset/cfi_restore instructions. Used to save or restore
+// the streaming value of VG around streaming-mode changes in locally-streaming
+// functions.
+def VGUnwindInfoPseudo :
+  Pseudo<(outs), (ins timm0_1:$save_restore), []>, Sched<[]>;
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kmclaughlin-arm wrote:

There wasn't any particular reason for only adding only pseudo, so I've split this out into two (VGSavePseudo & VGRestorePseudo).

https://github.com/llvm/llvm-project/pull/83301