[llvm] [RISCV] Add TSFlag for reading past VL behaviour. NFCI (PR #149704)

[Philip Reames via llvm-commits]

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@@ -58,7 +58,7 @@ class CustomRivosXVI<bits<6> funct6, RISCVVFormat opv, dag outs, dag ins,
 
 let Predicates = [HasVendorXRivosVizip], DecoderNamespace = "XRivos",
   Constraints = "@earlyclobber $vd", RVVConstraint = Vrgather,
-  Inst<6-0> = OPC_CUSTOM_2.Value in  {
+  Inst<6-0> = OPC_CUSTOM_2.Value, ReadsPastVL = 1 in  {
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preames wrote:

Not all of these can read past VL, but I'll fix this up in a following commit after I re-read the specification closely.  

https://github.com/llvm/llvm-project/pull/149704