[clang][ARM] Emit warnings when PACBTI-M is used with unsupported architectures

Branch protection in M-class is supported by
 - Armv8.1-M.Main
 - Armv8-M.Main
 - Armv7-M

Attempting to enable this for other architectures, either by
command-line (e.g -mbranch-protection=bti) or by target attribute
in source code (e.g.  __attribute__((target("branch-protection=..."))) )
will generate a warning.

In both cases function attributes related to branch protection will not
be emitted. Regardless of the warning, module level attributes related to
branch protection will be emitted when it is enabled via the command-line.

The following people also contributed to this patch:
- Victor Campos

Reviewed By: chill

Differential Revision: https://reviews.llvm.org/D115501

1 files changed, 32 insertions, 13 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index fb81169..3b5389ee 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -5563,8 +5563,8 @@ public:
 
     TargetInfo::BranchProtectionInfo BPI;
     StringRef Error;
-    (void)CGM.getTarget().validateBranchProtection(Attr.BranchProtection,
-                                                   BPI, Error);
+    (void)CGM.getTarget().validateBranchProtection(
+        Attr.BranchProtection, Attr.Architecture, BPI, Error);
     assert(Error.empty());
 
     auto *Fn = cast<llvm::Function>(GV);
@@ -6377,17 +6377,36 @@ public:
       if (!Attr.BranchProtection.empty()) {
         TargetInfo::BranchProtectionInfo BPI;
         StringRef DiagMsg;
-        (void)CGM.getTarget().validateBranchProtection(Attr.BranchProtection,
-                                                       BPI, DiagMsg);
-
-        static const char *SignReturnAddrStr[] = {"none", "non-leaf", "all"};
-        assert(static_cast<unsigned>(BPI.SignReturnAddr) <= 2 &&
-               "Unexpected SignReturnAddressScopeKind");
-        Fn->addFnAttr("sign-return-address",
-                      SignReturnAddrStr[static_cast<int>(BPI.SignReturnAddr)]);
-
-        Fn->addFnAttr("branch-target-enforcement",
-                      BPI.BranchTargetEnforcement ? "true" : "false");
+        StringRef Arch = Attr.Architecture.empty()
+                             ? CGM.getTarget().getTargetOpts().CPU
+                             : Attr.Architecture;
+        if (!CGM.getTarget().validateBranchProtection(Attr.BranchProtection,
+                                                      Arch, BPI, DiagMsg)) {
+          CGM.getDiags().Report(
+              D->getLocation(),
+              diag::warn_target_unsupported_branch_protection_attribute)
+              << Arch;
+        } else {
+          static const char *SignReturnAddrStr[] = {"none", "non-leaf", "all"};
+          assert(static_cast<unsigned>(BPI.SignReturnAddr) <= 2 &&
+                 "Unexpected SignReturnAddressScopeKind");
+          Fn->addFnAttr(
+              "sign-return-address",
+              SignReturnAddrStr[static_cast<int>(BPI.SignReturnAddr)]);
+
+          Fn->addFnAttr("branch-target-enforcement",
+                        BPI.BranchTargetEnforcement ? "true" : "false");
+        }
+      } else if (CGM.getLangOpts().BranchTargetEnforcement ||
+                 CGM.getLangOpts().hasSignReturnAddress()) {
+        // If the Branch Protection attribute is missing, validate the target
+        // Architecture attribute against Branch Protection command line
+        // settings.
+        if (!CGM.getTarget().isBranchProtectionSupportedArch(Attr.Architecture))
+          CGM.getDiags().Report(
+              D->getLocation(),
+              diag::warn_target_unsupported_branch_protection_attribute)
+              << Attr.Architecture;
       }
     }