[AArch64][PAC] Skip checking LR during tail call if FPAC is enabled

[atrosinenko]

Summary

If the target CPU implements optional FPAC feature, AUT* instruction
will fault by itself if pointer authentication fails, so skip the
explicit check.

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

 // This function may split MBB - in that case, the returned basic block
 // is the new block containing the return instruction.
 static MachineBasicBlock &checkAuthenticatedLR(MachineFunction &MF,
                                                MachineBasicBlock &MBB) {
   const auto &MFnI = *MF.getInfo<AArch64FunctionInfo>();
   if (!MFnI.shouldSignReturnAddress(MF))
     return MBB;
 
+  if (MF.getSubtarget<AArch64Subtarget>().hasFPAC())
+    return MBB;
+
   auto TI = MBB.getFirstTerminator();
   if (TI == MBB.end())
     return MBB;
 
   // Only explicitly check LR if we are performing tail call.
   Register TmpReg = AArch64::X16;
   switch (TI->getOpcode()) {
   case AArch64::TCRETURNdi:

llvm/test/CodeGen/AArch64/sign-return-address-tailcall.ll

 ; RUN: llc -mtriple=aarch64 -asm-verbose=0              < %s | FileCheck -DAUT="hint #29" --check-prefixes=COMMON,LDR %s
 ; RUN: llc -mtriple=aarch64 -asm-verbose=0 -mattr=v8.3a < %s | FileCheck -DAUT="autiasp"  --check-prefixes=COMMON,LDR %s
+; RUN: llc -mtriple=aarch64 -asm-verbose=0 -mattr=v8.3a,fpac < %s | FileCheck -DAUT="autiasp" --check-prefixes=COMMON,FPAC %s
 ; RUN: llc -mtriple=aarch64 -asm-verbose=0 -aarch64-check-authenticated-lr-by-load=0              < %s | FileCheck -DAUT="hint #29" -DXPAC="hint #7" --check-prefixes=COMMON,XPAC %s
 ; RUN: llc -mtriple=aarch64 -asm-verbose=0 -aarch64-check-authenticated-lr-by-load=0 -mattr=v8.3a < %s | FileCheck -DAUT="autiasp"  -DXPAC="xpaclri" --check-prefixes=COMMON,XPAC %s
+; RUN: llc -mtriple=aarch64 -asm-verbose=0 -aarch64-check-authenticated-lr-by-load=0 -mattr=v8.3a,fpac < %s | FileCheck -DAUT="autiasp" --check-prefixes=COMMON,FPAC %s
 
 define i32 @tailcall_direct() "sign-return-address"="non-leaf" {
 ; COMMON-LABEL: tailcall_direct:
 ; COMMON:         str x30, [sp, #-16]!
 ; COMMON:         ldr x30, [sp], #16
 ;
+; FPAC-NEXT:      [[AUT]]
+; FPAC-NEXT:      .cfi_negate_ra_state
+; FPAC-NEXT:      b callee
+;
 ; LDR-NEXT:       [[AUT]]
 ; LDR-NEXT:       .cfi_negate_ra_state
 ; LDR-NEXT:       ldr x16, [x30]
 ; LDR-NEXT:       b callee
 ;
 ; XPAC-NEXT:      [[AUT]]
 ; XPAC-NEXT:      .cfi_negate_ra_state
 ; XPAC-NEXT:      mov x16, x30
 ; XPAC-NEXT:      [[XPAC]]
 ; XPAC-NEXT:      cmp x16, x30
 ; XPAC-NEXT:      b.ne .[[FAIL:LBB[_0-9]+]]
 ; XPAC-NEXT:      b callee
 ; XPAC-NEXT:    .[[FAIL]]:
 ; XPAC-NEXT:      brk #0xc471
   tail call void asm sideeffect "", "~{lr}"()
   %call = tail call i32 @callee()
   ret i32 %call
 }
 
 define i32 @tailcall_indirect(ptr %fptr) "sign-return-address"="non-leaf" {
 ; COMMON-LABEL: tailcall_indirect:
 ; COMMON:         str x30, [sp, #-16]!
 ; COMMON:         ldr x30, [sp], #16
 ;
+; FPAC-NEXT:      [[AUT]]
+; FPAC-NEXT:      .cfi_negate_ra_state
+; FPAC-NEXT:      br x0
+;
 ; LDR-NEXT:       [[AUT]]
 ; LDR-NEXT:       .cfi_negate_ra_state
 ; LDR-NEXT:       ldr x16, [x30]
 ; LDR-NEXT:       br x0
 ;
 ; XPAC-NEXT:      [[AUT]]
 ; XPAC-NEXT:      .cfi_negate_ra_state
 ; XPAC-NEXT:      mov x16, x30
; COMMON-NEXT:    br x0
   ret i32 %call
 }
 
 define i32 @tailcall_direct_noframe_sign_all() "sign-return-address"="all" {
 ; COMMON-LABEL: tailcall_direct_noframe_sign_all:
 ; COMMON-NOT:     str{{.*}}x30
 ; COMMON-NOT:     ldr{{.*}}x30
 ;
+; FPAC:           [[AUT]]
+; FPAC-NEXT:      .cfi_negate_ra_state
+; FPAC-NEXT:      b callee
+;
 ; LDR:            [[AUT]]
 ; LDR-NEXT:       .cfi_negate_ra_state
 ; LDR-NEXT:       ldr x16, [x30]
 ; LDR-NEXT:       b callee
 ;
 ; XPAC:           [[AUT]]
 ; XPAC-NEXT:      .cfi_negate_ra_state
 ; XPAC-NEXT:      mov x16, x30
 ; XPAC-NEXT:      [[XPAC]]
 ; XPAC-NEXT:      cmp x16, x30
 ; XPAC-NEXT:      b.ne .[[FAIL:LBB[_0-9]+]]
 ; XPAC-NEXT:      b callee
 ; XPAC-NEXT:    .[[FAIL]]:
 ; XPAC-NEXT:      brk #0xc471
   %call = tail call i32 @callee()
   ret i32 %call
 }
 
 define i32 @tailcall_indirect_noframe_sign_all(ptr %fptr) "sign-return-address"="all" {
 ; COMMON-LABEL: tailcall_indirect_noframe_sign_all:
 ; COMMON-NOT:     str{{.*}}x30
 ; COMMON-NOT:     ldr{{.*}}x30
 ;
+; FPAC:           [[AUT]]
+; FPAC-NEXT:      .cfi_negate_ra_state
+; FPAC-NEXT:      br x0
+;
 ; LDR:            [[AUT]]
 ; LDR-NEXT:       .cfi_negate_ra_state
 ; LDR-NEXT:       ldr x16, [x30]
 ; LDR-NEXT:       br x0
 ;
 ; XPAC:           [[AUT]]
 ; XPAC-NEXT:      .cfi_negate_ra_state
 ; XPAC-NEXT:      mov x16, x30