[clang] [llvm] [AArch64] Support preserve_none calling convention (PR #91046)

[Andrew Pinski via cfe-commits]

================
@@ -5658,17 +5658,20 @@ experimental at this time.
 def PreserveNoneDocs : Documentation {
   let Category = DocCatCallingConvs;
   let Content = [{
-On X86-64 target, this attribute changes the calling convention of a function.
+On X86-64 and AArch64 targets, this attribute changes the calling convention of a function.
 The ``preserve_none`` calling convention tries to preserve as few general
 registers as possible. So all general registers are caller saved registers. It
 also uses more general registers to pass arguments. This attribute doesn't
-impact floating-point registers (XMMs/YMMs). Floating-point registers still
-follow the c calling convention.
-
-- Only RSP and RBP are preserved by callee.
-
-- Register RDI, RSI, RDX, RCX, R8, R9, R11, R12, R13, R14, R15 and RAX now can
-  be used to pass function arguments.
+impact floating-point registers.
+
+- On X86-64, only RSP and RBP are preserved by the callee.
+  Registers RDI, RSI, RDX, RCX, R8, R9, R11, R12, R13, R14, R15 and RAX now can
+  be used to pass function arguments. Floating-point registers (XMMs/YMMs) still
+  follow the C calling convention.
+- On AArch64, only LR and FP are preserved by the callee.
+  Registers X19-X28 and X0-X17 are used to pass function arguments.
----------------
pinskia wrote:

Even though you removed X16/X17 you seemly forgot to update the documentation.

https://github.com/llvm/llvm-project/pull/91046