[AArch64] Add -fbranch-target-identification alias to -mbranch-target-enforce.

Author: ahmedbougacha

clang/include/clang/Driver/Options.td

@@ -4384,6 +4384,10 @@ defm aarch64_jump_table_hardening: OptInCC1FFlag<"aarch64-jump-table-hardening",
 }
 
 let Group = f_Group in {
+  def fbranch_target_identification : Flag<["-"], "fbranch-target-identification">,
+      HelpText<"Emit branch target identification instructions for indirect branch destinations">;
+  def fno_branch_target_identification : Flag<["-"], "fno-branch-target-identification">;
+
   def fptrauth_objc_isa_mode : Joined<["-"], "fptrauth-objc-isa-mode=">,
       Visibility<[ClangOption, CC1Option, CC1AsOption]>,
       HelpText<"Authentication mode for ObjC isa field. Full auth if unspecified">, Values<"strip,sign-and-strip,sign-and-auth">;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -1910,6 +1910,9 @@ void Clang::AddAArch64TargetArgs(const ArgList &Args,
 
   // Enable/disable return address signing and indirect branch targets.
   CollectARMPACBTIOptions(getToolChain(), Args, CmdArgs, true /*isAArch64*/);
+  if (Args.hasArg(options::OPT_fbranch_target_identification,
+                  options::OPT_fno_branch_target_identification, false))
+    CmdArgs.push_back("-mbranch-target-enforce");
 }
 
 void Clang::AddLoongArchTargetArgs(const ArgList &Args,

clang/test/CodeGen/ptrauth-function-attributes.c

@@ -17,6 +17,8 @@
 // RUN: %clang_cc1 -triple arm64e-apple-ios  -faarch64-jump-table-hardening -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,JMPTBL
 // RUN: %clang_cc1 -triple aarch64-linux-gnu -faarch64-jump-table-hardening -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,JMPTBL
 
+// RUN: %clang_cc1 -triple arm64e-apple-ios  -mbranch-target-enforce -emit-llvm %s -o - | FileCheck %s --check-prefixes=ALL,BTI
+
 // ALL: define {{(dso_local )?}}void @test() #0
 void test() {
 }
@@ -31,4 +33,7 @@ void test() {
 
 // JMPTBL: attributes #0 = {{{.*}} "aarch64-jump-table-hardening" {{.*}}}
 
+// BTI: !1 = !{i32 8, !"branch-target-enforcement", i32 1}
+
 // OFF-NOT: attributes {{.*}} "ptrauth-
+// OFF-NOT: !"branch-target-enforcement"