[llvm] [SME] Stop RA from coalescing COPY instructions that transcend beyond smstart/smstop. (PR #78294)

[David Sherwood via llvm-commits]

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@@ -189,6 +191,26 @@ def : Pat<(int_aarch64_sme_set_tpidr2 i64:$val),
           (MSR 0xde85, GPR64:$val)>;
 def : Pat<(i64 (int_aarch64_sme_get_tpidr2)),
           (MRS 0xde85)>;
+
+multiclass CoalescerBarrierPseudo<RegisterClass rc, list<ValueType> vts> {
+  def NAME : Pseudo<(outs rc:$dst), (ins rc:$idx), []>, Sched<[]> {
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david-arm wrote:

nit: Is `$src` a better name instead of `$idx`, especially since you have the constraint `$dst = $idx`.

https://github.com/llvm/llvm-project/pull/78294