Minor refinements.

- assert ptrauth calls aren't used with PAuth_LR
- more const nits

Author: ahmedbougacha

llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp

@@ -791,7 +791,7 @@ static MachineInstr *createCallWithOps(MachineBasicBlock &MBB,
   // operands of the branch as it expects to be B <target> which is only one
   // operand. Instead they are implicit operands used by the branch.
   while (!MBBI->getOperand(RegMaskStartIdx).isRegMask()) {
-    MachineOperand &MOP = MBBI->getOperand(RegMaskStartIdx);
+    const MachineOperand &MOP = MBBI->getOperand(RegMaskStartIdx);
     assert(MOP.isReg() && "can only add register operands");
     Call->addOperand(MachineOperand::CreateReg(
         MOP.getReg(), /*Def=*/false, /*Implicit=*/true, /*isKill=*/false,
@@ -833,11 +833,11 @@ bool AArch64ExpandPseudo::expandCALL_RVMARKER(
   MachineInstr *OriginalCall = nullptr;
 
   if (MI.getOpcode() == AArch64::BLRA_RVMARKER) {
-    // Pointer auth call.
-    MachineOperand &CallTarget = MI.getOperand(1);
-    MachineOperand &Key = MI.getOperand(2);
-    MachineOperand &IntDisc = MI.getOperand(3);
-    MachineOperand &AddrDisc = MI.getOperand(4);
+    // ptrauth call.
+    const MachineOperand &CallTarget = MI.getOperand(1);
+    const MachineOperand &Key = MI.getOperand(2);
+    const MachineOperand &IntDisc = MI.getOperand(3);
+    const MachineOperand &AddrDisc = MI.getOperand(4);
 
     assert((Key.getImm() == AArch64PACKey::IA ||
             Key.getImm() == AArch64PACKey::IB) &&

llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp

@@ -1032,18 +1032,22 @@ static unsigned getCallOpcode(const MachineFunction &CallerF, bool IsIndirect,
   if (!IsIndirect)
     return AArch64::TCRETURNdi;
 
-  // When BTI is enabled, we need to use TCRETURNriBTI to make sure that we use
-  // x16 or x17.
+  // When BTI or PAuthLR are enabled, there are restrictions on using x16 and
+  // x17 to hold the function pointer.
   if (FuncInfo->branchTargetEnforcement()) {
+    if (FuncInfo->branchProtectionPAuthLR()) {
+      assert(!PAI && "ptrauth tail-calls not yet supported with PAuthLR");
+      return AArch64::TCRETURNrix17;
+    }
     if (PAI)
       return AArch64::AUTH_TCRETURN_BTI;
-    if (FuncInfo->branchProtectionPAuthLR())
-      return AArch64::TCRETURNrix17;
     return AArch64::TCRETURNrix16x17;
   }
 
-  if (FuncInfo->branchProtectionPAuthLR())
+  if (FuncInfo->branchProtectionPAuthLR()) {
+    assert(!PAI && "ptrauth tail-calls not yet supported with PAuthLR");
     return AArch64::TCRETURNrinotx16;
+  }
 
   if (PAI)
     return AArch64::AUTH_TCRETURN;