[llvm] [AArch64][SME] Introduce CHECK_MATCHING_VL pseudo for streaming transitions (PR #157510)

[Gaëtan Bossu via llvm-commits]

================
@@ -9732,7 +9815,8 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
   if (RequiresSMChange) {
     Chain =
         changeStreamingMode(DAG, DL, CallAttrs.callee().hasStreamingInterface(),
-                            Chain, InGlue, getSMToggleCondition(CallAttrs));
+                            Chain, InGlue, getSMToggleCondition(CallAttrs),
+                            CallConv == CallingConv::AArch64_SVE_VectorCall);
----------------
gbossu wrote:

Nit: to make the code more explicit without requiring a comment
```
bool InsertVectorLengthCheck = (CallConv == CallingConv::AArch64_SVE_VectorCall);
Chain =
        changeStreamingMode(DAG, DL, CallAttrs.callee().hasStreamingInterface(),
                            Chain, InGlue, getSMToggleCondition(CallAttrs));
                            Chain, InGlue, getSMToggleCondition(CallAttrs),
                            InsertVectorLengthCheck);
```

https://github.com/llvm/llvm-project/pull/157510