[llvm][AArch64] Autoupgrade function attributes from Module attribute…

…s. (#82763)

sign-return-address and similar module attributes should be propagated to
the function level before got merged because module flags may contradict and
this information is not recoverable.
Generated code will match with the normal linking flow.

Refactored version of  (#80640).
Run the attribute copy only during IRMove.

llvm/include/llvm/IR/AutoUpgrade.h

@@ -88,6 +88,9 @@ namespace llvm {
   /// info. Return true if module is modified.
   bool UpgradeDebugInfo(Module &M);
 
+  /// Copies module attributes to the functions in the module.
+  void CopyModuleAttrToFunctions(Module &M);
+
   /// Check whether a string looks like an old loop attachment tag.
   inline bool mayBeOldLoopAttachmentTag(StringRef Name) {
     return Name.starts_with("llvm.vectorizer.");

llvm/lib/IR/AutoUpgrade.cpp

@@ -5169,6 +5169,72 @@ void llvm::UpgradeFunctionAttributes(Function &F) {
     Arg.removeAttrs(AttributeFuncs::typeIncompatible(Arg.getType()));
 }
 
+// Check if the module attribute is present and not zero.
+static bool isModuleAttributeSet(Module &M, const StringRef &ModAttr) {
+  const auto *Attr =
+      mdconst::extract_or_null<ConstantInt>(M.getModuleFlag(ModAttr));
+  return Attr && Attr->getZExtValue();
+}
+
+// Copy an attribute from module to the function if exists.
+// First value of the pair is used when the module attribute is not zero
+// the second otherwise.
+static void
+CopyModuleAttributeToFunction(Function &F, StringRef FnAttrName,
+                              StringRef ModAttrName,
+                              std::pair<StringRef, StringRef> Values) {
+  if (F.hasFnAttribute(FnAttrName))
+    return;
+  F.addFnAttr(FnAttrName, isModuleAttributeSet(*F.getParent(), ModAttrName)
+                              ? Values.first
+                              : Values.second);
+}
+
+// Copy a boolean attribute from module to the function if exists.
+// Module attribute treated false if zero otherwise true.
+static void CopyModuleAttributeToFunction(Function &F, StringRef AttrName) {
+  CopyModuleAttributeToFunction(
+      F, AttrName, AttrName,
+      std::make_pair<StringRef, StringRef>("true", "false"));
+}
+
+// Copy an attribute from module to the function if exists.
+// First value of the pair is used when the module attribute is not zero
+// the second otherwise.
+static void
+CopyModuleAttributeToFunction(Function &F, StringRef AttrName,
+                              std::pair<StringRef, StringRef> Values) {
+  CopyModuleAttributeToFunction(F, AttrName, AttrName, Values);
+}
+
+void llvm::CopyModuleAttrToFunctions(Module &M) {
+  Triple T(M.getTargetTriple());
+  if (!T.isThumb() && !T.isARM() && !T.isAArch64())
+    return;
+
+  for (Function &F : M.getFunctionList()) {
+    if (F.isDeclaration())
+      continue;
+
+    if (!F.hasFnAttribute("sign-return-address")) {
+      StringRef SignType = "none";
+      if (isModuleAttributeSet(M, "sign-return-address"))
+        SignType = "non-leaf";
+
+      if (isModuleAttributeSet(M, "sign-return-address-all"))
+        SignType = "all";
+
+      F.addFnAttr("sign-return-address", SignType);
+    }
+    CopyModuleAttributeToFunction(F, "branch-target-enforcement");
+    CopyModuleAttributeToFunction(F, "branch-protection-pauth-lr");
+    CopyModuleAttributeToFunction(F, "guarded-control-stack");
+    CopyModuleAttributeToFunction(
+        F, "sign-return-address-key",
+        std::make_pair<StringRef, StringRef>("b_key", "a_key"));
+  }
+}
+
 static bool isOldLoopArgument(Metadata *MD) {
   auto *T = dyn_cast_or_null<MDTuple>(MD);
   if (!T)

llvm/lib/Linker/IRMover.cpp

@@ -1606,6 +1606,11 @@ Error IRLinker::run() {
   // Loop over all of the linked values to compute type mappings.
   computeTypeMapping();
 
+  // Convert module level attributes to function level attributes because
+  // after merging modules the attributes might change and would have different
+  // effect on the functions as the original module would have.
+  CopyModuleAttrToFunctions(*SrcM);
+
   std::reverse(Worklist.begin(), Worklist.end());
   while (!Worklist.empty()) {
     GlobalValue *GV = Worklist.back();

llvm/test/LTO/AArch64/link-branch-target-enforcement.ll

@@ -32,6 +32,7 @@ entry:
 ; CHECK-DUMP: <main>:
 ; CHECK-DUMP:      bl      0x8 <main+0x8>
 ; CHECK-DUMP: <foo>:
+; CHECK-DUMP:     paciasp
 
 ; `main` doesn't support BTI while `foo` does, so in the binary
 ; we should see only PAC which is supported by both.

llvm/test/LTO/AArch64/link-sign-return-address.ll

@@ -0,0 +1,43 @@
+; Testcase to check that module with different branch-target-enforcement can
+; be mixed.
+;
+; RUN: llvm-as %s -o %t1.bc
+; RUN: llvm-as %p/Inputs/foo.ll -o %t2.bc
+; RUN: llvm-lto -exported-symbol main \
+; RUN:          -exported-symbol foo \
+; RUN:          -filetype=obj \
+; RUN:           %t2.bc %t1.bc \
+; RUN:           -o %t1.exe 2>&1
+; RUN: llvm-objdump -d %t1.exe | FileCheck --check-prefix=CHECK-DUMP %s
+; RUN: llvm-readelf -n %t1.exe | FileCheck --allow-empty --check-prefix=CHECK-PROP %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64-unknown-linux-gnu"
+
+declare i32 @foo();
+
+define i32 @main() {
+entry:
+  %add = call i32 @foo()
+  ret i32 %add
+}
+
+!llvm.module.flags = !{!0, !1, !2, !3 }
+!0 = !{i32 8, !"branch-target-enforcement", i32 0}
+!1 = !{i32 8, !"sign-return-address", i32 0}
+!2 = !{i32 8, !"sign-return-address-all", i32 0}
+!3 = !{i32 8, !"sign-return-address-with-bkey", i32 0}
+
+; CHECK-DUMP: <foo>:
+; CHECK-DUMP:     paciasp
+; CHECK-DUMP:     mov     w0, #0x2a
+; CHECK-DUMP:     autiasp
+; CHECK-DUMP:     ret
+; CHECK-DUMP: <main>:
+; CHECK-DUMP-NOT:  paciasp
+; CHECK-DUMP:      str     x30,
+; CHECK-DUMP:      bl      0x14 <main+0x4>
+
+; `main` doesn't support PAC sign-return-address while `foo` does, so in the binary
+; we should not see anything.
+; CHECK-PROP-NOT:   Properties: aarch64 feature: PAC

llvm/test/Linker/link-arm-and-thumb.ll

@@ -13,11 +13,12 @@ entry:
   ret i32 %add
 }
 
-; CHECK: define i32 @main() {
+; CHECK: define i32 @main() [[MAIN_ATTRS:#[0-9]+]]
 ; CHECK: define i32 @foo(i32 %a, i32 %b) [[ARM_ATTRS:#[0-9]+]]
 ; CHECK: define i32 @bar(i32 %a, i32 %b) [[THUMB_ATTRS:#[0-9]+]]
 
-; CHECK: attributes [[ARM_ATTRS]] = { "target-features"="-thumb-mode" }
-; CHECK: attributes [[THUMB_ATTRS]] = { "target-features"="+thumb-mode" }
+; CHECK: attributes [[MAIN_ATTRS]] = { {{.*}} }
+; CHECK: attributes [[ARM_ATTRS]] = { {{.*}} "target-features"="-thumb-mode" }
+; CHECK: attributes [[THUMB_ATTRS]] = { {{.*}} "target-features"="+thumb-mode" }
 
 ; STDERR-NOT: warning: Linking two modules of different target triples: