[llvm] [AArch64][GlobalISel] Implement selectVaStartAAPCS (PR #106979)

[Thorsten Schütt via llvm-commits]

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@@ -1994,7 +1994,108 @@ bool AArch64InstructionSelector::selectVectorAshrLshr(
 
 bool AArch64InstructionSelector::selectVaStartAAPCS(
     MachineInstr &I, MachineFunction &MF, MachineRegisterInfo &MRI) const {
-  return false;
+
+  if (MF.getSubtarget<AArch64Subtarget>().isCallingConvWin64(
+          MF.getFunction().getCallingConv(), MF.getFunction().isVarArg()))
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tschuett wrote:

Is test over specified? `isVarArg()` is implied by the function name. What about `isWindowsArm64EC()` ?  What about `isTargetWindows()` ? Or is it under specified?

https://github.com/llvm/llvm-project/pull/106979