[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 <[email protected]>

Author: shashforge

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) {

llvm/test/CodeGen/AArch64/bti-ehpad.ll

@@ -0,0 +1,22 @@
+; llvm/test/CodeGen/AArch64/bti-ehpad.ll
+; REQUIRES: aarch64-registered-target
+; RUN: llc -mtriple=aarch64-none-linux-gnu -mattr=+bti %s -o - | FileCheck %s
+
+define void @test() #0 personality i8* undef {
+entry:
+  invoke void @may_throw()
+          to label %ret unwind label %lpad
+lpad:                               ; catch.dispatch
+  landingpad { i8*, i32 }
+          cleanup
+  ret void
+ret:
+  ret void
+}
+
+declare void @may_throw()
+
+; Function needs both the architectural feature *and* the enforcement request.
+attributes #0 = { "branch-target-enforcement"="true" "target-features"="+bti" }
+
+; CHECK:      bti j