[AArch64] Fix operand definitions of XPACI/XPACD

[chill]

Summary

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.

[danielkiss]

LGTM

llvm/lib/Target/AArch64/AArch64InstrFormats.td

class SignAuthTwoOperand<bits<4> opc, string asm,
   let Inst{31-21} = 0b10011010110;
   let Inst{20-16} = Rm;
   let Inst{15-14} = 0b00;
   let Inst{13-10} = opc;
   let Inst{9-5}   = Rn;
   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, "", []>,
       Sched<[WriteI, ReadI, ReadI]> {
   let Uses = [NZCV];
   let Defs = [NZCV];
   bits<5> Rn;
   let Inst{31}    = sf;

llvm/lib/Target/AArch64/AArch64InstrInfo.td

multiclass SignAuth<bits<3> prefix, bits<3> prefix_z, string asm> {
     def DZA  : SignAuthZero<prefix_z, 0b10, !strconcat(asm, "dza")>;
     def IZB  : SignAuthZero<prefix_z, 0b01, !strconcat(asm, "izb")>;
     def DZB  : SignAuthZero<prefix_z, 0b11, !strconcat(asm, "dzb")>;
   }
 
   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
   let isBranch = 1, isTerminator = 1, isBarrier = 1, isIndirectBranch = 1  in {
     def BRAA    : AuthBranchTwoOperands<0, 0, "braa">;
     def BRAB    : AuthBranchTwoOperands<0, 1, "brab">;
   }
   let isCall = 1, Defs = [LR], Uses = [SP] in {