[llvm] [AArch64][SME] Implement the SME ABI (ZA state management) in Machine IR (PR #149062)

[Paul Walker via llvm-commits]

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@@ -9014,14 +9025,26 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
       CallConv = CallingConv::AArch64_SVE_VectorCall;
   }
 
+  bool UseNewSMEABILowering = Subtarget->useNewSMEABILowering();
+  bool IsAgnosticZAFunction = CallAttrs.caller().hasAgnosticZAInterface();
+  auto ZAMarkerNode = [&]() -> std::optional<unsigned> {
+    // TODO: Handle agnostic ZA functions.
+    if (!UseNewSMEABILowering || IsAgnosticZAFunction)
+      return std::nullopt;
+    if (!CallAttrs.caller().hasZAState() && !CallAttrs.caller().hasZT0State())
+      return std::nullopt;
+    return CallAttrs.requiresLazySave() ? AArch64ISD::REQUIRES_ZA_SAVE
+                                        : AArch64ISD::INOUT_ZA_USE;
+  }();
+
   if (IsTailCall) {
     // Check if it's really possible to do a tail call.
     IsTailCall = isEligibleForTailCallOptimization(CLI);
 
     // A sibling call is one where we're under the usual C ABI and not planning
     // to change that but can still do a tail call:
-    if (!TailCallOpt && IsTailCall && CallConv != CallingConv::Tail &&
-        CallConv != CallingConv::SwiftTail)
+    if (!ZAMarkerNode.has_value() && !TailCallOpt && IsTailCall &&
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paulwalker-arm wrote:

Does just `!ZAMarkerNode` not work here?

https://github.com/llvm/llvm-project/pull/149062