[AArch64] Fix for BTI landing pad insertion with PAC-RET+bkey.

[danielkiss]

Summary

EMITBKEY is emitted for PAC-RET+bkey, which is a non machine instructions.

PR: 49957

[eugenis]

I don't think this is correct in general - check AArch64ExpandPseudoInsts.cpp for a long list of pseudos that are replaced with real machine instructions.

[danielkiss]

Ah, right. EMITBKEY should be a meta one but it seems as a problematic change.
Let's simplify this now and hope no other need to be added too.

[eugenis]

LGTM, thanks!

llvm/lib/Target/AArch64/AArch64BranchTargets.cpp

void AArch64BranchTargets::addBTI(MachineBasicBlock &MBB, bool CouldCall,
   if (CouldCall)
     HintNum |= 2;
   if (CouldJump)
     HintNum |= 4;
   assert(HintNum != 32 && "No target kinds!");
 
   auto MBBI = MBB.begin();
 
-  // Skip the meta instuctions, those will be removed anyway.
-  for (; MBBI != MBB.end() && MBBI->isMetaInstruction(); ++MBBI)
+  // Skip the meta instructions, those will be removed anyway.
+  for (; MBBI != MBB.end() &&
+         (MBBI->isMetaInstruction() || MBBI->getOpcode() == AArch64::EMITBKEY);
+       ++MBBI)
     ;
 
   // SCTLR_EL1.BT[01] is set to 0 by default which means
   // PACI[AB]SP are implicitly BTI C so no BTI C instruction is needed there.
   if (MBBI != MBB.end() && HintNum == 34 &&
       (MBBI->getOpcode() == AArch64::PACIASP ||
        MBBI->getOpcode() == AArch64::PACIBSP))
     return;
 
   BuildMI(MBB, MBB.begin(), MBB.findDebugLoc(MBB.begin()),
           TII->get(AArch64::HINT))
       .addImm(HintNum);
 }

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

 ; CHECK-LABEL: @leaf_sign_all_v83_b_key
 ; CHECK: pacibsp
 ; CHECK-NOT: ret
 ; CHECK: retab
 ; CHECK-NOT: ret
 define i32 @leaf_sign_all_v83_b_key(i32 %x) "sign-return-address"="all" "target-features"="+v8.3a" "sign-return-address-key"="b_key" {
   ret i32 %x
 }
+
+; CHECK-LABEL: @leaf_sign_all_a_key_bti
+; CHECK-NOT:   hint #34
+; CHECK:       hint #25
+; CHECK:       hint #29
+; CHECK-V83A:  paciasp
+; CHECK-V83A:  retaa
+define i32 @leaf_sign_all_a_key_bti(i32 %x) "sign-return-address"="all" "sign-return-address-key"="a_key" "branch-target-enforcement"="true"{
+  ret i32 %x
+}
+
+; CHECK-LABEL: @leaf_sign_all_b_key_bti
+; CHECK-NOT:   hint #34
+; CHECK:       hint #27
+; CHECK:       hint #31
+; CHECK-V83A:  pacibsp
+; CHECK-V83A:  retab
+define i32 @leaf_sign_all_b_key_bti(i32 %x) "sign-return-address"="all" "sign-return-address-key"="b_key" "branch-target-enforcement"="true"{
+  ret i32 %x
+}
+
+; CHECK-LABEL: @leaf_sign_all_v83_b_key_bti
+; CHECK-NOT:   hint #34
+; CHECK: pacibsp
+; CHECK-NOT: ret
+; CHECK: retab
+; CHECK-NOT: ret
+define i32 @leaf_sign_all_v83_b_key_bti(i32 %x) "sign-return-address"="all" "target-features"="+v8.3a" "sign-return-address-key"="b_key" "branch-target-enforcement"="true" {
+  ret i32 %x
+}