[clang] [llvm] [ARM][AArch64] BTI, GCS, PAC Module flag update. (PR #86212)

[Andrew Savonichev via llvm-commits]

================
@@ -5296,6 +5296,106 @@ void llvm::UpgradeFunctionAttributes(Function &F) {
   }
 }
 
+// Check if the module attribute is present and set to one.
+static bool isModuleAttributeOne(Module &M, const StringRef &ModAttr) {
+  const auto *Attr =
+      mdconst::extract_or_null<ConstantInt>(M.getModuleFlag(ModAttr));
+  return Attr && Attr->isOne();
+}
+
+// Check if the module attribute is present and set to two.
+static bool isModuleAttributeTwo(Module &M, const StringRef &ModAttr) {
+  const auto *Attr =
+      mdconst::extract_or_null<ConstantInt>(M.getModuleFlag(ModAttr));
+  return Attr && Attr->getZExtValue() == 2;
+}
+
+// Check if the function attribute is not present and set it.
+static void SetFunctionAttrIfNotSet(Function &F, StringRef FnAttrName,
+                                    StringRef Value) {
+  if (!F.hasFnAttribute(FnAttrName))
+    F.addFnAttr(FnAttrName, Value);
+}
+
+// Check if the function attribute is not present and set it if needed.
+// If the attribute is "false" then removes it.
+// If the attribute is "true" resets it to a valueless attribute.
+static void ConvertFunctionAttr(Function &F, bool Set, StringRef FnAttrName) {
+  if (!F.hasFnAttribute(FnAttrName)) {
+    if (Set)
+      F.addFnAttr(FnAttrName);
+  } else {
+    auto A = F.getFnAttribute(FnAttrName);
+    if ("false" == A.getValueAsString())
+      F.removeFnAttr(FnAttrName);
+    else if ("true" == A.getValueAsString()) {
+      F.removeFnAttr(FnAttrName);
+      F.addFnAttr(FnAttrName);
+    }
+  }
+}
+
+void llvm::CopyModuleAttrToFunctions(Module &M) {
+  Triple T(M.getTargetTriple());
+  if (!T.isThumb() && !T.isARM() && !T.isAArch64())
+    return;
+
+  if (isModuleAttributeTwo(M, "branch-target-enforcement"))
----------------
asavonic wrote:

`isModuleAttributeTwo` and `isModuleAttributeOne` call [Module::getModuleFlag](https://github.com/llvm/llvm-project/blob/674491928c9ae8ec25bde79044894570988202ea/llvm/lib/IR/Module.cpp#L357) function, which is a loop for each flag. This may look and perform better if we traverse flags only once, extract them as integers, and then do all the processing, like we do in [UpgradeModuleFlags](https://github.com/llvm/llvm-project/blob/99b6f2bc9c472fe930e216cf4cc72dd5cdbf14d7/llvm/lib/IR/AutoUpgrade.cpp#L5089).

https://github.com/llvm/llvm-project/pull/86212