[llvm] [AArch64] Emit BTI j on EH landing pads () (PR #149680)

[Shashi Shankar via llvm-commits]

https://github.com/shashforge created https://github.com/llvm/llvm-project/pull/149680

Landing pads reached by the unwinder are entered via 'br', so they must start with BTI j when -mbranch-protection requests BTI.  Add isEHPad() to the jump-target test.

Size/perf: +4 B per pad only when BTI is enabled.

Test: new CodeGen/AArch64/bti-ehpad.ll.

>From 7a02decd59bcde371bc395889e740a1762d4c0ee Mon Sep 17 00:00:00 2001
From: Shashi Shankar <shashishankar1687 at gmail.com>
Date: Sun, 20 Jul 2025 00:11:28 +0200
Subject: [PATCH] [AArch64] Emit BTI j on EH landing pads ()

Landing pads reached by the unwinder are entered via 'br', so they must
start with BTI j when -mbranch-protection requests BTI.  Add isEHPad()
to the jump-target test.

Size/perf: +4 B per pad only when BTI is enabled.

Test: new CodeGen/AArch64/bti-ehpad.ll.
Signed-off-by: Shashi Shankar <shashishankar1687 at gmail.com>
---
 .../lib/Target/AArch64/AArch64BranchTargets.cpp |  2 +-
 llvm/test/CodeGen/AArch64/bti-ehpad.ll          | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/AArch64/bti-ehpad.ll

diff --git a/llvm/lib/Target/AArch64/AArch64BranchTargets.cpp b/llvm/lib/Target/AArch64/AArch64BranchTargets.cpp
index 3436dc9ef4521..1999195051aa5 100644
--- a/llvm/lib/Target/AArch64/AArch64BranchTargets.cpp
+++ b/llvm/lib/Target/AArch64/AArch64BranchTargets.cpp
@@ -100,7 +100,7 @@ bool AArch64BranchTargets::runOnMachineFunction(MachineFunction &MF) {
     // If the block itself is address-taken, it could be indirectly branched
     // to, but not called.
     if (MBB.isMachineBlockAddressTaken() || MBB.isIRBlockAddressTaken() ||
-        JumpTableTargets.count(&MBB))
+        JumpTableTargets.count(&MBB) || MBB.isEHPad())
       CouldJump = true;
 
     if (CouldCall || CouldJump) {
diff --git a/llvm/test/CodeGen/AArch64/bti-ehpad.ll b/llvm/test/CodeGen/AArch64/bti-ehpad.ll
new file mode 100644
index 0000000000000..dda4a54b723d3
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/bti-ehpad.ll
@@ -0,0 +1,17 @@
+; RUN: llc -mtriple=aarch64-linux-gnu -mbranch-protection=standard %s -o - | FileCheck %s
+
+declare i32 @__gxx_personality_v0(...)
+
+define void @foo() personality ptr @__gxx_personality_v0 {
+entry:
+  invoke void @bar() to label %exit unwind label %lpad
+
+lpad:                                    ; CHECK-LABEL: lpad:
+  landingpad { ptr, i32 } cleanup        ; CHECK:       bti     j
+  resume { ptr null, i32 0 }
+
+exit:
+  ret void
+}
+
+declare void @bar()