[llvm] [AArch64] Remove dead code emission in Pointer Authentication (PR #175989)

via llvm-commits llvm-commits at lists.llvm.org
Wed Jan 14 08:49:23 PST 2026 

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: Victor Campos (vhscampos)

<details>
<summary>Changes</summary>

The AArch64 Pointer Authentication pass was emitting address materialization instructions that were never used. These instructions formed dead code and served no purpose in the final control flow.

Remove the unnecessary ADRP/ADD sequence from the Pointer Auth codegen and update the corresponding test to reflect the simplified output.

This avoids generating dead instructions and keeps the PAUTH LR sequence minimal and correct.

---
Full diff: https://github.com/llvm/llvm-project/pull/175989.diff


2 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64PointerAuth.cpp (-2) 
- (modified) llvm/test/CodeGen/AArch64/sign-return-address-pauth-lr.ll (-26) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/AArch64PointerAuth.cpp b/llvm/lib/Target/AArch64/AArch64PointerAuth.cpp
index 8bd7a7cb5a74a..9726c4c789f50 100644
--- a/llvm/lib/Target/AArch64/AArch64PointerAuth.cpp
+++ b/llvm/lib/Target/AArch64/AArch64PointerAuth.cpp
@@ -185,7 +185,6 @@ void AArch64PointerAuth::authenticateLR(
       !MF.getFunction().hasFnAttribute(Attribute::ShadowCallStack)) {
     if (MFnI->branchProtectionPAuthLR() && Subtarget->hasPAuthLR()) {
       assert(PACSym && "No PAC instruction to refer to");
-      emitPACSymOffsetIntoX16(*TII, MBB, MBBI, DL, PACSym);
       BuildMI(MBB, TI, DL,
               TII->get(UseBKey ? AArch64::RETABSPPCi : AArch64::RETAASPPCi))
           .addSym(PACSym)
@@ -201,7 +200,6 @@ void AArch64PointerAuth::authenticateLR(
   } else {
     if (MFnI->branchProtectionPAuthLR() && Subtarget->hasPAuthLR()) {
       assert(PACSym && "No PAC instruction to refer to");
-      emitPACSymOffsetIntoX16(*TII, MBB, MBBI, DL, PACSym);
       emitPACCFI(MBB, MBBI, MachineInstr::FrameDestroy, EmitAsyncCFI);
       BuildMI(MBB, MBBI, DL,
               TII->get(UseBKey ? AArch64::AUTIBSPPCi : AArch64::AUTIASPPCi))
diff --git a/llvm/test/CodeGen/AArch64/sign-return-address-pauth-lr.ll b/llvm/test/CodeGen/AArch64/sign-return-address-pauth-lr.ll
index d533ca1159183..4f9c3c7de70a1 100644
--- a/llvm/test/CodeGen/AArch64/sign-return-address-pauth-lr.ll
+++ b/llvm/test/CodeGen/AArch64/sign-return-address-pauth-lr.ll
@@ -85,8 +85,6 @@ define i32 @leaf_sign_all(i32 %x) "branch-protection-pauth-lr" "sign-return-addr
 ; PAUTHLR-NEXT:    .cfi_negate_ra_state_with_pc
 ; PAUTHLR-NEXT:  .Ltmp0:
 ; PAUTHLR-NEXT:    paciasppc
-; PAUTHLR-NEXT:    adrp x16, .Ltmp0
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp0
 ; PAUTHLR-NEXT:    retaasppc .Ltmp0
   ret i32 %x
 }
@@ -141,8 +139,6 @@ define i64 @leaf_clobbers_lr(i64 %x) "branch-protection-pauth-lr" "sign-return-a
 ; PAUTHLR-NEXT:    mov x30, x0
 ; PAUTHLR-NEXT:    //NO_APP
 ; PAUTHLR-NEXT:    ldr x30, [sp], #16 // 8-byte Folded Reload
-; PAUTHLR-NEXT:    adrp x16, .Ltmp1
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp1
 ; PAUTHLR-NEXT:    retaasppc .Ltmp1
   call void asm sideeffect "mov x30, $0", "r,~{lr}"(i64 %x) #1
   ret i64 %x
@@ -194,8 +190,6 @@ define i32 @non_leaf_sign_all(i32 %x) "branch-protection-pauth-lr" "sign-return-
 ; PAUTHLR-NEXT:    .cfi_offset w30, -16
 ; PAUTHLR-NEXT:    bl foo
 ; PAUTHLR-NEXT:    ldr x30, [sp], #16 // 8-byte Folded Reload
-; PAUTHLR-NEXT:    adrp x16, .Ltmp2
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp2
 ; PAUTHLR-NEXT:    retaasppc .Ltmp2
   %call = call i32 @foo(i32 %x)
   ret i32 %call
@@ -245,8 +239,6 @@ define i32 @non_leaf_sign_non_leaf(i32 %x) "branch-protection-pauth-lr" "sign-re
 ; PAUTHLR-NEXT:    .cfi_offset w30, -16
 ; PAUTHLR-NEXT:    bl foo
 ; PAUTHLR-NEXT:    ldr x30, [sp], #16 // 8-byte Folded Reload
-; PAUTHLR-NEXT:    adrp x16, .Ltmp3
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp3
 ; PAUTHLR-NEXT:    retaasppc .Ltmp3
   %call = call i32 @foo(i32 %x)
   ret i32 %call
@@ -287,8 +279,6 @@ define i32 @non_leaf_scs(i32 %x) "branch-protection-pauth-lr" "sign-return-addre
 ; PAUTHLR-NEXT:    bl foo
 ; PAUTHLR-NEXT:    ldr x30, [sp], #16 // 8-byte Folded Reload
 ; PAUTHLR-NEXT:    ldr x30, [x18, #-8]!
-; PAUTHLR-NEXT:    adrp x16, .Ltmp4
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp4
 ; PAUTHLR-NEXT:    autiasppc .Ltmp4
 ; PAUTHLR-NEXT:    ret
   %call = call i32 @foo(i32 %x)
@@ -312,8 +302,6 @@ define i32 @leaf_sign_all_v83(i32 %x) "branch-protection-pauth-lr" "sign-return-
 ; PAUTHLR-NEXT:    .cfi_negate_ra_state_with_pc
 ; PAUTHLR-NEXT:  .Ltmp5:
 ; PAUTHLR-NEXT:    paciasppc
-; PAUTHLR-NEXT:    adrp x16, .Ltmp5
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp5
 ; PAUTHLR-NEXT:    retaasppc .Ltmp5
   ret i32 %x
 }
@@ -371,8 +359,6 @@ define fastcc void @spill_lr_and_tail_call(i64 %x) "branch-protection-pauth-lr"
 ; PAUTHLR-NEXT:    mov x30, x0
 ; PAUTHLR-NEXT:    //NO_APP
 ; PAUTHLR-NEXT:    ldr x30, [sp], #16 // 8-byte Folded Reload
-; PAUTHLR-NEXT:    adrp x16, .Ltmp6
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp6
 ; PAUTHLR-NEXT:    autiasppc .Ltmp6
 ; PAUTHLR-NEXT:    b bar
   call void asm sideeffect "mov x30, $0", "r,~{lr}"(i64 %x) #1
@@ -409,8 +395,6 @@ define i32 @leaf_sign_all_a_key(i32 %x) "branch-protection-pauth-lr" "sign-retur
 ; PAUTHLR-NEXT:    .cfi_negate_ra_state_with_pc
 ; PAUTHLR-NEXT:  .Ltmp7:
 ; PAUTHLR-NEXT:    paciasppc
-; PAUTHLR-NEXT:    adrp x16, .Ltmp7
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp7
 ; PAUTHLR-NEXT:    retaasppc .Ltmp7
   ret i32 %x
 }
@@ -447,8 +431,6 @@ define i32 @leaf_sign_all_b_key(i32 %x) "branch-protection-pauth-lr" "sign-retur
 ; PAUTHLR-NEXT:    .cfi_negate_ra_state_with_pc
 ; PAUTHLR-NEXT:  .Ltmp8:
 ; PAUTHLR-NEXT:    pacibsppc
-; PAUTHLR-NEXT:    adrp x16, .Ltmp8
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp8
 ; PAUTHLR-NEXT:    retabsppc .Ltmp8
   ret i32 %x
 }
@@ -472,8 +454,6 @@ define i32 @leaf_sign_all_v83_b_key(i32 %x) "branch-protection-pauth-lr" "sign-r
 ; PAUTHLR-NEXT:    .cfi_negate_ra_state_with_pc
 ; PAUTHLR-NEXT:  .Ltmp9:
 ; PAUTHLR-NEXT:    pacibsppc
-; PAUTHLR-NEXT:    adrp x16, .Ltmp9
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp9
 ; PAUTHLR-NEXT:    retabsppc .Ltmp9
   ret i32 %x
 }
@@ -511,8 +491,6 @@ define i32 @leaf_sign_all_a_key_bti(i32 %x) "branch-protection-pauth-lr" "sign-r
 ; PAUTHLR-NEXT:    bti c
 ; PAUTHLR-NEXT:  .Ltmp10:
 ; PAUTHLR-NEXT:    paciasppc
-; PAUTHLR-NEXT:    adrp x16, .Ltmp10
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp10
 ; PAUTHLR-NEXT:    retaasppc .Ltmp10
   ret i32 %x
 }
@@ -553,8 +531,6 @@ define i32 @leaf_sign_all_b_key_bti(i32 %x) "branch-protection-pauth-lr" "sign-r
 ; PAUTHLR-NEXT:    bti c
 ; PAUTHLR-NEXT:  .Ltmp11:
 ; PAUTHLR-NEXT:    pacibsppc
-; PAUTHLR-NEXT:    adrp x16, .Ltmp11
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp11
 ; PAUTHLR-NEXT:    retabsppc .Ltmp11
   ret i32 %x
 }
@@ -581,8 +557,6 @@ define i32 @leaf_sign_all_v83_b_key_bti(i32 %x) "branch-protection-pauth-lr" "si
 ; PAUTHLR-NEXT:    bti c
 ; PAUTHLR-NEXT:  .Ltmp12:
 ; PAUTHLR-NEXT:    pacibsppc
-; PAUTHLR-NEXT:    adrp x16, .Ltmp12
-; PAUTHLR-NEXT:    add x16, x16, :lo12:.Ltmp12
 ; PAUTHLR-NEXT:    retabsppc .Ltmp12
   ret i32 %x
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/175989

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