[AArch64] Fix operand definitions of XPACI/XPACD

The operand to these instructions is both input and output.

These are not yet emitted by the compiler and the assembler already
works fine, so can't test in this patch.  But D75044 will use XPACI
and provide test coverage for this patch as well.

Differential Revision: https://reviews.llvm.org/D84298

llvm/lib/Target/AArch64/AArch64InstrFormats.td

@@ -1937,6 +1937,15 @@ class SignAuthTwoOperand<bits<4> opc, string asm,
   let Inst{4-0}   = Rd;
 }
 
+class ClearAuth<bits<1> data, string asm>
+  : I<(outs GPR64:$Rd), (ins GPR64:$Rn), asm, "\t$Rd", "$Rd = $Rn", []>, Sched<[]> {
+  bits<5> Rd;
+  let Inst{31-11} = 0b110110101100000101000;
+  let Inst{10} = data;
+  let Inst{9-5} = 0b11111;
+  let Inst{4-0} = Rd;
+}
+
 // Base class for the Armv8.4-A 8 and 16-bit flag manipulation instructions
 class BaseFlagManipulation<bit sf, bit sz, dag iops, string asm, string ops>
     : I<(outs), iops, asm, ops, "", []>,

llvm/lib/Target/AArch64/AArch64InstrInfo.td

@@ -994,8 +994,8 @@ let Predicates = [HasPA] in {
   defm PAC : SignAuth<0b000, 0b010, "pac">;
   defm AUT : SignAuth<0b001, 0b011, "aut">;
 
-  def XPACI : SignAuthZero<0b100, 0b00, "xpaci">;
-  def XPACD : SignAuthZero<0b100, 0b01, "xpacd">;
+  def XPACI : ClearAuth<0, "xpaci">;
+  def XPACD : ClearAuth<1, "xpacd">;
   def PACGA : SignAuthTwoOperand<0b1100, "pacga", null_frag>;
 
   // Combined Instructions