[llvm] [Aarch64] [ISel] Don't save vaargs registers if vaargs are unused (PR #126780)

[Eli Friedman via llvm-commits]

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@@ -8189,7 +8189,7 @@ SDValue AArch64TargetLowering::LowerFormalArguments(
   }
 
   // varargs
-  if (isVarArg) {
+  if (isVarArg && DAG.getMachineFunction().getFrameInfo().hasVAStart()) {
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efriedma-quic wrote:

As long as it works with `-global-isel-abort=0`, you're fine; you don't need to implement G_VASTART on any target where it isn't already implemented.

https://github.com/llvm/llvm-project/pull/126780