[AArch64] Codegen support for FEAT_PAuthLR

- Adds a new +pc option to -mbranch-protection that will enable
  the use of PC as a diversifier in PAC branch protection code.

- When +pauth-lr is enabled (-march=armv9.5a+pauth-lr) in combination
  with -mbranch-protection=pac-ret+pc, the new 9.5-a instructions
  (pacibsppc, retaasppc, etc) are used.

Documentation for the relevant instructions can be found here:
https://developer.arm.com/documentation/ddi0602/2023-09/Base-Instructions/

Co-authored-by: Lucas Prates <lucas.prates@arm.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index b2e173d0..d78f259 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1106,6 +1106,9 @@ void CodeGenModule::Release() {
     if (LangOpts.BranchTargetEnforcement)
       getModule().addModuleFlag(llvm::Module::Min, "branch-target-enforcement",
                                 1);
+    if (LangOpts.BranchProtectionPAuthLR)
+      getModule().addModuleFlag(llvm::Module::Min, "branch-protection-pauth-lr",
+                                1);
     if (LangOpts.hasSignReturnAddress())
       getModule().addModuleFlag(llvm::Module::Min, "sign-return-address", 1);
     if (LangOpts.isSignReturnAddressScopeAll())